/* * linux/mm/vmscan.c * * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds * * Swap reorganised 29.12.95, Stephen Tweedie. * kswapd added: 7.1.96 sct * Removed kswapd_ctl limits, and swap out as many pages as needed * to bring the system back to freepages.high: 2.4.97, Rik van Riel. * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). * Multiqueue VM started 5.8.00, Rik van Riel. */ #include <linux/mm.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/kernel_stat.h> #include <linux/swap.h> #include <linux/pagemap.h> #include <linux/init.h> #include <linux/highmem.h> #include <linux/vmstat.h> #include <linux/file.h> #include <linux/writeback.h> #include <linux/blkdev.h> #include <linux/buffer_head.h> /* for try_to_release_page(), buffer_heads_over_limit */ #include <linux/mm_inline.h> #include <linux/pagevec.h> #include <linux/backing-dev.h> #include <linux/rmap.h> #include <linux/topology.h> #include <linux/cpu.h> #include <linux/cpuset.h> #include <linux/notifier.h> #include <linux/rwsem.h> #include <linux/delay.h> #include <linux/kthread.h> #include <linux/freezer.h> #include <linux/memcontrol.h> #include <linux/delayacct.h> #include <linux/sysctl.h> #include <asm/tlbflush.h> #include <asm/div64.h> #include <linux/swapops.h> #include "internal.h" struct scan_control { /* Incremented by the number of inactive pages that were scanned */ unsigned long nr_scanned; /* Number of pages freed so far during a call to shrink_zones() */ unsigned long nr_reclaimed; /* This context's GFP mask */ gfp_t gfp_mask; int may_writepage; /* Can pages be swapped as part of reclaim? */ int may_swap; /* This context's SWAP_CLUSTER_MAX. If freeing memory for * suspend, we effectively ignore SWAP_CLUSTER_MAX. * In this context, it doesn't matter that we scan the * whole list at once. */ int swap_cluster_max; int swappiness; int all_unreclaimable; int order; /* Which cgroup do we reclaim from */ struct mem_cgroup *mem_cgroup; /* Pluggable isolate pages callback */ unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst, unsigned long *scanned, int order, int mode, struct zone *z, struct mem_cgroup *mem_cont, int active, int file); }; #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) #ifdef ARCH_HAS_PREFETCH #define prefetch_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetch(&prev->_field); \ } \ } while (0) #else #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) #endif #ifdef ARCH_HAS_PREFETCHW #define prefetchw_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetchw(&prev->_field); \ } \ } while (0) #else #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) #endif /* * From 0 .. 100. Higher means more swappy. */ int vm_swappiness = 60; long vm_total_pages; /* The total number of pages which the VM controls */ static LIST_HEAD(shrinker_list); static DECLARE_RWSEM(shrinker_rwsem); #ifdef CONFIG_CGROUP_MEM_RES_CTLR #define scanning_global_lru(sc) (!(sc)->mem_cgroup) #else #define scanning_global_lru(sc) (1) #endif static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone, struct scan_control *sc) { if (!scanning_global_lru(sc)) return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone); return &zone->reclaim_stat; } static unsigned long zone_nr_pages(struct zone *zone, struct scan_control *sc, enum lru_list lru) { if (!scanning_global_lru(sc)) return mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, lru); return zone_page_state(zone, NR_LRU_BASE + lru); } /* * Add a shrinker callback to be called from the vm */ void register_shrinker(struct shrinker *shrinker) { shrinker->nr = 0; down_write(&shrinker_rwsem); list_add_tail(&shrinker->list, &shrinker_list); up_write(&shrinker_rwsem); } EXPORT_SYMBOL(register_shrinker); /* * Remove one */ void unregister_shrinker(struct shrinker *shrinker) { down_write(&shrinker_rwsem); list_del(&shrinker->list); up_write(&shrinker_rwsem); } EXPORT_SYMBOL(unregister_shrinker); #define SHRINK_BATCH 128 /* * Call the shrink functions to age shrinkable caches * * Here we assume it costs one seek to replace a lru page and that it also * takes a seek to recreate a cache object. With this in mind we age equal * percentages of the lru and ageable caches. This should balance the seeks * generated by these structures. * * If the vm encountered mapped pages on the LRU it increase the pressure on * slab to avoid swapping. * * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. * * `lru_pages' represents the number of on-LRU pages in all the zones which * are eligible for the caller's allocation attempt. It is used for balancing * slab reclaim versus page reclaim. * * Returns the number of slab objects which we shrunk. */ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages) { struct shrinker *shrinker; unsigned long ret = 0; if (scanned == 0) scanned = SWAP_CLUSTER_MAX; if (!down_read_trylock(&shrinker_rwsem)) return 1; /* Assume we'll be able to shrink next time */ list_for_each_entry(shrinker, &shrinker_list, list) { unsigned long long delta; unsigned long total_scan; unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask); delta = (4 * scanned) / shrinker->seeks; delta *= max_pass; do_div(delta, lru_pages + 1); shrinker->nr += delta; if (shrinker->nr < 0) { printk(KERN_ERR "%s: nr=%ld\n", __func__, shrinker->nr); shrinker->nr = max_pass; } /* * Avoid risking looping forever due to too large nr value: * never try to free more than twice the estimate number of * freeable entries. */ if (shrinker->nr > max_pass * 2) shrinker->nr = max_pass * 2; total_scan = shrinker->nr; shrinker->nr = 0; while (total_scan >= SHRINK_BATCH) { long this_scan = SHRINK_BATCH; int shrink_ret; int nr_before; nr_before = (*shrinker->shrink)(0, gfp_mask); shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask); if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; count_vm_events(SLABS_SCANNED, this_scan); total_scan -= this_scan; cond_resched(); } shrinker->nr += total_scan; } up_read(&shrinker_rwsem); return ret; } /* Called without lock on whether page is mapped, so answer is unstable */ static inline int page_mapping_inuse(struct page *page) { struct address_space *mapping; /* Page is in somebody's page tables. */ if (page_mapped(page)) return 1; /* Be more reluctant to reclaim swapcache than pagecache */ if (PageSwapCache(page)) return 1; mapping = page_mapping(page); if (!mapping) return 0; /* File is mmap'd by somebody? */ return mapping_mapped(mapping); } static inline int is_page_cache_freeable(struct page *page) { return page_count(page) - !!PagePrivate(page) == 2; } static int may_write_to_queue(struct backing_dev_info *bdi) { if (current->flags & PF_SWAPWRITE) return 1; if (!bdi_write_congested(bdi)) return 1; if (bdi == current->backing_dev_info) return 1; return 0; } /* * We detected a synchronous write error writing a page out. Probably * -ENOSPC. We need to propagate that into the address_space for a subsequent * fsync(), msync() or close(). * * The tricky part is that after writepage we cannot touch the mapping: nothing * prevents it from being freed up. But we have a ref on the page and once * that page is locked, the mapping is pinned. * * We're allowed to run sleeping lock_page() here because we know the caller has * __GFP_FS. */ static void handle_write_error(struct address_space *mapping, struct page *page, int error) { lock_page(page); if (page_mapping(page) == mapping) mapping_set_error(mapping, error); unlock_page(page); } /* Request for sync pageout. */ enum pageout_io { PAGEOUT_IO_ASYNC, PAGEOUT_IO_SYNC, }; /* possible outcome of pageout() */ typedef enum { /* failed to write page out, page is locked */ PAGE_KEEP, /* move page to the active list, page is locked */ PAGE_ACTIVATE, /* page has been sent to the disk successfully, page is unlocked */ PAGE_SUCCESS, /* page is clean and locked */ PAGE_CLEAN, } pageout_t; /* * pageout is called by shrink_page_list() for each dirty page. * Calls ->writepage(). */ static pageout_t pageout(struct page *page, struct address_space *mapping, enum pageout_io sync_writeback) { /* * If the page is dirty, only perform writeback if that write * will be non-blocking. To prevent this allocation from being * stalled by pagecache activity. But note that there may be * stalls if we need to run get_block(). We could test * PagePrivate for that. * * If this process is currently in generic_file_write() against * this page's queue, we can perform writeback even if that * will block. * * If the page is swapcache, write it back even if that would * block, for some throttling. This happens by accident, because * swap_backing_dev_info is bust: it doesn't reflect the * congestion state of the swapdevs. Easy to fix, if needed. * See swapfile.c:page_queue_congested(). */ if (!is_page_cache_freeable(page)) return PAGE_KEEP; if (!mapping) { /* * Some data journaling orphaned pages can have * page->mapping == NULL while being dirty with clean buffers. */ if (PagePrivate(page)) { if (try_to_free_buffers(page)) { ClearPageDirty(page); printk("%s: orphaned page\n", __func__); return PAGE_CLEAN; } } return PAGE_KEEP; } if (mapping->a_ops->writepage == NULL) return PAGE_ACTIVATE; if (!may_write_to_queue(mapping->backing_dev_info)) return PAGE_KEEP; if (clear_page_dirty_for_io(page)) { int res; struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .nr_to_write = SWAP_CLUSTER_MAX, .range_start = 0, .range_end = LLONG_MAX, .nonblocking = 1, .for_reclaim = 1, }; SetPageReclaim(page); res = mapping->a_ops->writepage(page, &wbc); if (res < 0) handle_write_error(mapping, page, res); if (res == AOP_WRITEPAGE_ACTIVATE) { ClearPageReclaim(page); return PAGE_ACTIVATE; } /* * Wait on writeback if requested to. This happens when * direct reclaiming a large contiguous area and the * first attempt to free a range of pages fails. */ if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC) wait_on_page_writeback(page); if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); } inc_zone_page_state(page, NR_VMSCAN_WRITE); return PAGE_SUCCESS; } return PAGE_CLEAN; } /* * Same as remove_mapping, but if the page is removed from the mapping, it * gets returned with a refcount of 0. */ static int __remove_mapping(struct address_space *mapping, struct page *page) { BUG_ON(!PageLocked(page)); BUG_ON(mapping != page_mapping(page)); spin_lock_irq(&mapping->tree_lock); /* * The non racy check for a busy page. * * Must be careful with the order of the tests. When someone has * a ref to the page, it may be possible that they dirty it then * drop the reference. So if PageDirty is tested before page_count * here, then the following race may occur: * * get_user_pages(&page); * [user mapping goes away] * write_to(page); * !PageDirty(page) [good] * SetPageDirty(page); * put_page(page); * !page_count(page) [good, discard it] * * [oops, our write_to data is lost] * * Reversing the order of the tests ensures such a situation cannot * escape unnoticed. The smp_rmb is needed to ensure the page->flags * load is not satisfied before that of page->_count. * * Note that if SetPageDirty is always performed via set_page_dirty, * and thus under tree_lock, then this ordering is not required. */ if (!page_freeze_refs(page, 2)) goto cannot_free; /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ if (unlikely(PageDirty(page))) { page_unfreeze_refs(page, 2); goto cannot_free; } if (PageSwapCache(page)) { swp_entry_t swap = { .val = page_private(page) }; __delete_from_swap_cache(page); spin_unlock_irq(&mapping->tree_lock); swap_free(swap); } else { __remove_from_page_cache(page); spin_unlock_irq(&mapping->tree_lock); } return 1; cannot_free: spin_unlock_irq(&mapping->tree_lock); return 0; } /* * Attempt to detach a locked page from its ->mapping. If it is dirty or if * someone else has a ref on the page, abort and return 0. If it was * successfully detached, return 1. Assumes the caller has a single ref on * this page. */ int remove_mapping(struct address_space *mapping, struct page *page) { if (__remove_mapping(mapping, page)) { /* * Unfreezing the refcount with 1 rather than 2 effectively * drops the pagecache ref for us without requiring another * atomic operation. */ page_unfreeze_refs(page, 1); return 1; } return 0; } /** * putback_lru_page - put previously isolated page onto appropriate LRU list * @page: page to be put back to appropriate lru list * * Add previously isolated @page to appropriate LRU list. * Page may still be unevictable for other reasons. * * lru_lock must not be held, interrupts must be enabled. */ #ifdef CONFIG_UNEVICTABLE_LRU void putback_lru_page(struct page *page) { int lru; int active = !!TestClearPageActive(page); int was_unevictable = PageUnevictable(page); VM_BUG_ON(PageLRU(page)); redo: ClearPageUnevictable(page); if (page_evictable(page, NULL)) { /* * For evictable pages, we can use the cache. * In event of a race, worst case is we end up with an * unevictable page on [in]active list. * We know how to handle that. */ lru = active + page_is_file_cache(page); lru_cache_add_lru(page, lru); } else { /* * Put unevictable pages directly on zone's unevictable * list. */ lru = LRU_UNEVICTABLE; add_page_to_unevictable_list(page); } /* * page's status can change while we move it among lru. If an evictable * page is on unevictable list, it never be freed. To avoid that, * check after we added it to the list, again. */ if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) { if (!isolate_lru_page(page)) { put_page(page); goto redo; } /* This means someone else dropped this page from LRU * So, it will be freed or putback to LRU again. There is * nothing to do here. */ } if (was_unevictable && lru != LRU_UNEVICTABLE) count_vm_event(UNEVICTABLE_PGRESCUED); else if (!was_unevictable && lru == LRU_UNEVICTABLE) count_vm_event(UNEVICTABLE_PGCULLED); put_page(page); /* drop ref from isolate */ } #else /* CONFIG_UNEVICTABLE_LRU */ void putback_lru_page(struct page *page) { int lru; VM_BUG_ON(PageLRU(page)); lru = !!TestClearPageActive(page) + page_is_file_cache(page); lru_cache_add_lru(page, lru); put_page(page); } #endif /* CONFIG_UNEVICTABLE_LRU */ /* * shrink_page_list() returns the number of reclaimed pages */ static unsigned long shrink_page_list(struct list_head *page_list, struct scan_control *sc, enum pageout_io sync_writeback) { LIST_HEAD(ret_pages); struct pagevec freed_pvec; int pgactivate = 0; unsigned long nr_reclaimed = 0; cond_resched(); pagevec_init(&freed_pvec, 1); while (!list_empty(page_list)) { struct address_space *mapping; struct page *page; int may_enter_fs; int referenced; cond_resched(); page = lru_to_page(page_list); list_del(&page->lru); if (!trylock_page(page)) goto keep; VM_BUG_ON(PageActive(page)); sc->nr_scanned++; if (unlikely(!page_evictable(page, NULL))) goto cull_mlocked; if (!sc->may_swap && page_mapped(page)) goto keep_locked; /* Double the slab pressure for mapped and swapcache pages */ if (page_mapped(page) || PageSwapCache(page)) sc->nr_scanned++; may_enter_fs = (sc->gfp_mask & __GFP_FS) || (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); if (PageWriteback(page)) { /* * Synchronous reclaim is performed in two passes, * first an asynchronous pass over the list to * start parallel writeback, and a second synchronous * pass to wait for the IO to complete. Wait here * for any page for which writeback has already * started. */ if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs) wait_on_page_writeback(page); else goto keep_locked; } referenced = page_referenced(page, 1, sc->mem_cgroup); /* In active use or really unfreeable? Activate it. */ if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced && page_mapping_inuse(page)) goto activate_locked; /* * Anonymous process memory has backing store? * Try to allocate it some swap space here. */ if (PageAnon(page) && !PageSwapCache(page)) { if (!(sc->gfp_mask & __GFP_IO)) goto keep_locked; if (!add_to_swap(page)) goto activate_locked; may_enter_fs = 1; } mapping = page_mapping(page); /* * The page is mapped into the page tables of one or more * processes. Try to unmap it here. */ if (page_mapped(page) && mapping) { switch (try_to_unmap(page, 0)) { case SWAP_FAIL: goto activate_locked; case SWAP_AGAIN: goto keep_locked; case SWAP_MLOCK: goto cull_mlocked; case SWAP_SUCCESS: ; /* try to free the page below */ } } if (PageDirty(page)) { if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced) goto keep_locked; if (!may_enter_fs) goto keep_locked; if (!sc->may_writepage) goto keep_locked; /* Page is dirty, try to write it out here */ switch (pageout(page, mapping, sync_writeback)) { case PAGE_KEEP: goto keep_locked; case PAGE_ACTIVATE: goto activate_locked; case PAGE_SUCCESS: if (PageWriteback(page) || PageDirty(page)) goto keep; /* * A synchronous write - probably a ramdisk. Go * ahead and try to reclaim the page. */ if (!trylock_page(page)) goto keep; if (PageDirty(page) || PageWriteback(page)) goto keep_locked; mapping = page_mapping(page); case PAGE_CLEAN: ; /* try to free the page below */ } } /* * If the page has buffers, try to free the buffer mappings * associated with this page. If we succeed we try to free * the page as well. * * We do this even if the page is PageDirty(). * try_to_release_page() does not perform I/O, but it is * possible for a page to have PageDirty set, but it is actually * clean (all its buffers are clean). This happens if the * buffers were written out directly, with submit_bh(). ext3 * will do this, as well as the blockdev mapping. * try_to_release_page() will discover that cleanness and will * drop the buffers and mark the page clean - it can be freed. * * Rarely, pages can have buffers and no ->mapping. These are * the pages which were not successfully invalidated in * truncate_complete_page(). We try to drop those buffers here * and if that worked, and the page is no longer mapped into * process address space (page_count == 1) it can be freed. * Otherwise, leave the page on the LRU so it is swappable. */ if (PagePrivate(page)) { if (!try_to_release_page(page, sc->gfp_mask)) goto activate_locked; if (!mapping && page_count(page) == 1) { unlock_page(page); if (put_page_testzero(page)) goto free_it; else { /* * rare race with speculative reference. * the speculative reference will free * this page shortly, so we may * increment nr_reclaimed here (and * leave it off the LRU). */ nr_reclaimed++; continue; } } } if (!mapping || !__remove_mapping(mapping, page)) goto keep_locked; /* * At this point, we have no other references and there is * no way to pick any more up (removed from LRU, removed * from pagecache). Can use non-atomic bitops now (and * we obviously don't have to worry about waking up a process * waiting on the page lock, because there are no references. */ __clear_page_locked(page); free_it: nr_reclaimed++; if (!pagevec_add(&freed_pvec, page)) { __pagevec_free(&freed_pvec); pagevec_reinit(&freed_pvec); } continue; cull_mlocked: if (PageSwapCache(page)) try_to_free_swap(page); unlock_page(page); putback_lru_page(page); continue; activate_locked: /* Not a candidate for swapping, so reclaim swap space. */ if (PageSwapCache(page) && vm_swap_full()) try_to_free_swap(page); VM_BUG_ON(PageActive(page)); SetPageActive(page); pgactivate++; keep_locked: unlock_page(page); keep: list_add(&page->lru, &ret_pages); VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); } list_splice(&ret_pages, page_list); if (pagevec_count(&freed_pvec)) __pagevec_free(&freed_pvec); count_vm_events(PGACTIVATE, pgactivate); return nr_reclaimed; } /* LRU Isolation modes. */ #define ISOLATE_INACTIVE 0 /* Isolate inactive pages. */ #define ISOLATE_ACTIVE 1 /* Isolate active pages. */ #define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */ /* * Attempt to remove the specified page from its LRU. Only take this page * if it is of the appropriate PageActive status. Pages which are being * freed elsewhere are also ignored. * * page: page to consider * mode: one of the LRU isolation modes defined above * * returns 0 on success, -ve errno on failure. */ int __isolate_lru_page(struct page *page, int mode, int file) { int ret = -EINVAL; /* Only take pages on the LRU. */ if (!PageLRU(page)) return ret; /* * When checking the active state, we need to be sure we are * dealing with comparible boolean values. Take the logical not * of each. */ if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode)) return ret; if (mode != ISOLATE_BOTH && (!page_is_file_cache(page) != !file)) return ret; /* * When this function is being called for lumpy reclaim, we * initially look into all LRU pages, active, inactive and * unevictable; only give shrink_page_list evictable pages. */ if (PageUnevictable(page)) return ret; ret = -EBUSY; if (likely(get_page_unless_zero(page))) { /* * Be careful not to clear PageLRU until after we're * sure the page is not being freed elsewhere -- the * page release code relies on it. */ ClearPageLRU(page); ret = 0; mem_cgroup_del_lru(page); } return ret; } /* * zone->lru_lock is heavily contended. Some of the functions that * shrink the lists perform better by taking out a batch of pages * and working on them outside the LRU lock. * * For pagecache intensive workloads, this function is the hottest * spot in the kernel (apart from copy_*_user functions). * * Appropriate locks must be held before calling this function. * * @nr_to_scan: The number of pages to look through on the list. * @src: The LRU list to pull pages off. * @dst: The temp list to put pages on to. * @scanned: The number of pages that were scanned. * @order: The caller's attempted allocation order * @mode: One of the LRU isolation modes * @file: True [1] if isolating file [!anon] pages * * returns how many pages were moved onto *@dst. */ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, struct list_head *src, struct list_head *dst, unsigned long *scanned, int order, int mode, int file) { unsigned long nr_taken = 0; unsigned long scan; for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { struct page *page; unsigned long pfn; unsigned long end_pfn; unsigned long page_pfn; int zone_id; page = lru_to_page(src); prefetchw_prev_lru_page(page, src, flags); VM_BUG_ON(!PageLRU(page)); switch (__isolate_lru_page(page, mode, file)) { case 0: list_move(&page->lru, dst); nr_taken++; break; case -EBUSY: /* else it is being freed elsewhere */ list_move(&page->lru, src); continue; default: BUG(); } if (!order) continue; /* * Attempt to take all pages in the order aligned region * surrounding the tag page. Only take those pages of * the same active state as that tag page. We may safely * round the target page pfn down to the requested order * as the mem_map is guarenteed valid out to MAX_ORDER, * where that page is in a different zone we will detect * it from its zone id and abort this block scan. */ zone_id = page_zone_id(page); page_pfn = page_to_pfn(page); pfn = page_pfn & ~((1 << order) - 1); end_pfn = pfn + (1 << order); for (; pfn < end_pfn; pfn++) { struct page *cursor_page; /* The target page is in the block, ignore it. */ if (unlikely(pfn == page_pfn)) continue; /* Avoid holes within the zone. */ if (unlikely(!pfn_valid_within(pfn))) break; cursor_page = pfn_to_page(pfn); /* Check that we have not crossed a zone boundary. */ if (unlikely(page_zone_id(cursor_page) != zone_id)) continue; switch (__isolate_lru_page(cursor_page, mode, file)) { case 0: list_move(&cursor_page->lru, dst); nr_taken++; scan++; break; case -EBUSY: /* else it is being freed elsewhere */ list_move(&cursor_page->lru, src); default: break; /* ! on LRU or wrong list */ } } } *scanned = scan; return nr_taken; } static unsigned long isolate_pages_global(unsigned long nr, struct list_head *dst, unsigned long *scanned, int order, int mode, struct zone *z, struct mem_cgroup *mem_cont, int active, int file) { int lru = LRU_BASE; if (active) lru += LRU_ACTIVE; if (file) lru += LRU_FILE; return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order, mode, !!file); } /* * clear_active_flags() is a helper for shrink_active_list(), clearing * any active bits from the pages in the list. */ static unsigned long clear_active_flags(struct list_head *page_list, unsigned int *count) { int nr_active = 0; int lru; struct page *page; list_for_each_entry(page, page_list, lru) { lru = page_is_file_cache(page); if (PageActive(page)) { lru += LRU_ACTIVE; ClearPageActive(page); nr_active++; } count[lru]++; } return nr_active; } /** * isolate_lru_page - tries to isolate a page from its LRU list * @page: page to isolate from its LRU list * * Isolates a @page from an LRU list, clears PageLRU and adjusts the * vmstat statistic corresponding to whatever LRU list the page was on. * * Returns 0 if the page was removed from an LRU list. * Returns -EBUSY if the page was not on an LRU list. * * The returned page will have PageLRU() cleared. If it was found on * the active list, it will have PageActive set. If it was found on * the unevictable list, it will have the PageUnevictable bit set. That flag * may need to be cleared by the caller before letting the page go. * * The vmstat statistic corresponding to the list on which the page was * found will be decremented. * * Restrictions: * (1) Must be called with an elevated refcount on the page. This is a * fundamentnal difference from isolate_lru_pages (which is called * without a stable reference). * (2) the lru_lock must not be held. * (3) interrupts must be enabled. */ int isolate_lru_page(struct page *page) { int ret = -EBUSY; if (PageLRU(page)) { struct zone *zone = page_zone(page); spin_lock_irq(&zone->lru_lock); if (PageLRU(page) && get_page_unless_zero(page)) { int lru = page_lru(page); ret = 0; ClearPageLRU(page); del_page_from_lru_list(zone, page, lru); } spin_unlock_irq(&zone->lru_lock); } return ret; } /* * shrink_inactive_list() is a helper for shrink_zone(). It returns the number * of reclaimed pages */ static unsigned long shrink_inactive_list(unsigned long max_scan, struct zone *zone, struct scan_control *sc, int priority, int file) { LIST_HEAD(page_list); struct pagevec pvec; unsigned long nr_scanned = 0; unsigned long nr_reclaimed = 0; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); pagevec_init(&pvec, 1); lru_add_drain(); spin_lock_irq(&zone->lru_lock); do { struct page *page; unsigned long nr_taken; unsigned long nr_scan; unsigned long nr_freed; unsigned long nr_active; unsigned int count[NR_LRU_LISTS] = { 0, }; int mode = ISOLATE_INACTIVE; /* * If we need a large contiguous chunk of memory, or have * trouble getting a small set of contiguous pages, we * will reclaim both active and inactive pages. * * We use the same threshold as pageout congestion_wait below. */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) mode = ISOLATE_BOTH; else if (sc->order && priority < DEF_PRIORITY - 2) mode = ISOLATE_BOTH; nr_taken = sc->isolate_pages(sc->swap_cluster_max, &page_list, &nr_scan, sc->order, mode, zone, sc->mem_cgroup, 0, file); nr_active = clear_active_flags(&page_list, count); __count_vm_events(PGDEACTIVATE, nr_active); __mod_zone_page_state(zone, NR_ACTIVE_FILE, -count[LRU_ACTIVE_FILE]); __mod_zone_page_state(zone, NR_INACTIVE_FILE, -count[LRU_INACTIVE_FILE]); __mod_zone_page_state(zone, NR_ACTIVE_ANON, -count[LRU_ACTIVE_ANON]); __mod_zone_page_state(zone, NR_INACTIVE_ANON, -count[LRU_INACTIVE_ANON]); if (scanning_global_lru(sc)) zone->pages_scanned += nr_scan; reclaim_stat->recent_scanned[0] += count[LRU_INACTIVE_ANON]; reclaim_stat->recent_scanned[0] += count[LRU_ACTIVE_ANON]; reclaim_stat->recent_scanned[1] += count[LRU_INACTIVE_FILE]; reclaim_stat->recent_scanned[1] += count[LRU_ACTIVE_FILE]; spin_unlock_irq(&zone->lru_lock); nr_scanned += nr_scan; nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC); /* * If we are direct reclaiming for contiguous pages and we do * not reclaim everything in the list, try again and wait * for IO to complete. This will stall high-order allocations * but that should be acceptable to the caller */ if (nr_freed < nr_taken && !current_is_kswapd() && sc->order > PAGE_ALLOC_COSTLY_ORDER) { congestion_wait(WRITE, HZ/10); /* * The attempt at page out may have made some * of the pages active, mark them inactive again. */ nr_active = clear_active_flags(&page_list, count); count_vm_events(PGDEACTIVATE, nr_active); nr_freed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC); } nr_reclaimed += nr_freed; local_irq_disable(); if (current_is_kswapd()) { __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan); __count_vm_events(KSWAPD_STEAL, nr_freed); } else if (scanning_global_lru(sc)) __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan); __count_zone_vm_events(PGSTEAL, zone, nr_freed); if (nr_taken == 0) goto done; spin_lock(&zone->lru_lock); /* * Put back any unfreeable pages. */ while (!list_empty(&page_list)) { int lru; page = lru_to_page(&page_list); VM_BUG_ON(PageLRU(page)); list_del(&page->lru); if (unlikely(!page_evictable(page, NULL))) { spin_unlock_irq(&zone->lru_lock); putback_lru_page(page); spin_lock_irq(&zone->lru_lock); continue; } SetPageLRU(page); lru = page_lru(page); add_page_to_lru_list(zone, page, lru); if (PageActive(page)) { int file = !!page_is_file_cache(page); reclaim_stat->recent_rotated[file]++; } if (!pagevec_add(&pvec, page)) { spin_unlock_irq(&zone->lru_lock); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } } while (nr_scanned < max_scan); spin_unlock(&zone->lru_lock); done: local_irq_enable(); pagevec_release(&pvec); return nr_reclaimed; } /* * We are about to scan this zone at a certain priority level. If that priority * level is smaller (ie: more urgent) than the previous priority, then note * that priority level within the zone. This is done so that when the next * process comes in to scan this zone, it will immediately start out at this * priority level rather than having to build up its own scanning priority. * Here, this priority affects only the reclaim-mapped threshold. */ static inline void note_zone_scanning_priority(struct zone *zone, int priority) { if (priority < zone->prev_priority) zone->prev_priority = priority; } /* * This moves pages from the active list to the inactive list. * * We move them the other way if the page is referenced by one or more * processes, from rmap. * * If the pages are mostly unmapped, the processing is fast and it is * appropriate to hold zone->lru_lock across the whole operation. But if * the pages are mapped, the processing is slow (page_referenced()) so we * should drop zone->lru_lock around each page. It's impossible to balance * this, so instead we remove the pages from the LRU while processing them. * It is safe to rely on PG_active against the non-LRU pages in here because * nobody will play with that bit on a non-LRU page. * * The downside is that we have to touch page->_count against each page. * But we had to alter page->flags anyway. */ static void shrink_active_list(unsigned long nr_pages, struct zone *zone, struct scan_control *sc, int priority, int file) { unsigned long pgmoved; int pgdeactivate = 0; unsigned long pgscanned; LIST_HEAD(l_hold); /* The pages which were snipped off */ LIST_HEAD(l_inactive); struct page *page; struct pagevec pvec; enum lru_list lru; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); lru_add_drain(); spin_lock_irq(&zone->lru_lock); pgmoved = sc->isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order, ISOLATE_ACTIVE, zone, sc->mem_cgroup, 1, file); /* * zone->pages_scanned is used for detect zone's oom * mem_cgroup remembers nr_scan by itself. */ if (scanning_global_lru(sc)) { zone->pages_scanned += pgscanned; } reclaim_stat->recent_scanned[!!file] += pgmoved; if (file) __mod_zone_page_state(zone, NR_ACTIVE_FILE, -pgmoved); else __mod_zone_page_state(zone, NR_ACTIVE_ANON, -pgmoved); spin_unlock_irq(&zone->lru_lock); pgmoved = 0; while (!list_empty(&l_hold)) { cond_resched(); page = lru_to_page(&l_hold); list_del(&page->lru); if (unlikely(!page_evictable(page, NULL))) { putback_lru_page(page); continue; } /* page_referenced clears PageReferenced */ if (page_mapping_inuse(page) && page_referenced(page, 0, sc->mem_cgroup)) pgmoved++; list_add(&page->lru, &l_inactive); } /* * Move the pages to the [file or anon] inactive list. */ pagevec_init(&pvec, 1); pgmoved = 0; lru = LRU_BASE + file * LRU_FILE; spin_lock_irq(&zone->lru_lock); /* * Count referenced pages from currently used mappings as * rotated, even though they are moved to the inactive list. * This helps balance scan pressure between file and anonymous * pages in get_scan_ratio. */ reclaim_stat->recent_rotated[!!file] += pgmoved; while (!list_empty(&l_inactive)) { page = lru_to_page(&l_inactive); prefetchw_prev_lru_page(page, &l_inactive, flags); VM_BUG_ON(PageLRU(page)); SetPageLRU(page); VM_BUG_ON(!PageActive(page)); ClearPageActive(page); list_move(&page->lru, &zone->lru[lru].list); mem_cgroup_add_lru_list(page, lru); pgmoved++; if (!pagevec_add(&pvec, page)) { __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); spin_unlock_irq(&zone->lru_lock); pgdeactivate += pgmoved; pgmoved = 0; if (buffer_heads_over_limit) pagevec_strip(&pvec); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); pgdeactivate += pgmoved; if (buffer_heads_over_limit) { spin_unlock_irq(&zone->lru_lock); pagevec_strip(&pvec); spin_lock_irq(&zone->lru_lock); } __count_zone_vm_events(PGREFILL, zone, pgscanned); __count_vm_events(PGDEACTIVATE, pgdeactivate); spin_unlock_irq(&zone->lru_lock); if (vm_swap_full()) pagevec_swap_free(&pvec); pagevec_release(&pvec); } static int inactive_anon_is_low_global(struct zone *zone) { unsigned long active, inactive; active = zone_page_state(zone, NR_ACTIVE_ANON); inactive = zone_page_state(zone, NR_INACTIVE_ANON); if (inactive * zone->inactive_ratio < active) return 1; return 0; } /** * inactive_anon_is_low - check if anonymous pages need to be deactivated * @zone: zone to check * @sc: scan control of this context * * Returns true if the zone does not have enough inactive anon pages, * meaning some active anon pages need to be deactivated. */ static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) { int low; if (scanning_global_lru(sc)) low = inactive_anon_is_low_global(zone); else low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup); return low; } static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, struct zone *zone, struct scan_control *sc, int priority) { int file = is_file_lru(lru); if (lru == LRU_ACTIVE_FILE) { shrink_active_list(nr_to_scan, zone, sc, priority, file); return 0; } if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) { shrink_active_list(nr_to_scan, zone, sc, priority, file); return 0; } return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); } /* * Determine how aggressively the anon and file LRU lists should be * scanned. The relative value of each set of LRU lists is determined * by looking at the fraction of the pages scanned we did rotate back * onto the active list instead of evict. * * percent[0] specifies how much pressure to put on ram/swap backed * memory, while percent[1] determines pressure on the file LRUs. */ static void get_scan_ratio(struct zone *zone, struct scan_control *sc, unsigned long *percent) { unsigned long anon, file, free; unsigned long anon_prio, file_prio; unsigned long ap, fp; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); /* If we have no swap space, do not bother scanning anon pages. */ if (nr_swap_pages <= 0) { percent[0] = 0; percent[1] = 100; return; } anon = zone_nr_pages(zone, sc, LRU_ACTIVE_ANON) + zone_nr_pages(zone, sc, LRU_INACTIVE_ANON); file = zone_nr_pages(zone, sc, LRU_ACTIVE_FILE) + zone_nr_pages(zone, sc, LRU_INACTIVE_FILE); if (scanning_global_lru(sc)) { free = zone_page_state(zone, NR_FREE_PAGES); /* If we have very few page cache pages, force-scan anon pages. */ if (unlikely(file + free <= zone->pages_high)) { percent[0] = 100; percent[1] = 0; return; } } /* * OK, so we have swap space and a fair amount of page cache * pages. We use the recently rotated / recently scanned * ratios to determine how valuable each cache is. * * Because workloads change over time (and to avoid overflow) * we keep these statistics as a floating average, which ends * up weighing recent references more than old ones. * * anon in [0], file in [1] */ if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { spin_lock_irq(&zone->lru_lock); reclaim_stat->recent_scanned[0] /= 2; reclaim_stat->recent_rotated[0] /= 2; spin_unlock_irq(&zone->lru_lock); } if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { spin_lock_irq(&zone->lru_lock); reclaim_stat->recent_scanned[1] /= 2; reclaim_stat->recent_rotated[1] /= 2; spin_unlock_irq(&zone->lru_lock); } /* * With swappiness at 100, anonymous and file have the same priority. * This scanning priority is essentially the inverse of IO cost. */ anon_prio = sc->swappiness; file_prio = 200 - sc->swappiness; /* * The amount of pressure on anon vs file pages is inversely * proportional to the fraction of recently scanned pages on * each list that were recently referenced and in active use. */ ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1); ap /= reclaim_stat->recent_rotated[0] + 1; fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1); fp /= reclaim_stat->recent_rotated[1] + 1; /* Normalize to percentages */ percent[0] = 100 * ap / (ap + fp + 1); percent[1] = 100 - percent[0]; } /* * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. */ static void shrink_zone(int priority, struct zone *zone, struct scan_control *sc) { unsigned long nr[NR_LRU_LISTS]; unsigned long nr_to_scan; unsigned long percent[2]; /* anon @ 0; file @ 1 */ enum lru_list l; unsigned long nr_reclaimed = sc->nr_reclaimed; unsigned long swap_cluster_max = sc->swap_cluster_max; get_scan_ratio(zone, sc, percent); for_each_evictable_lru(l) { int file = is_file_lru(l); int scan; scan = zone_page_state(zone, NR_LRU_BASE + l); if (priority) { scan >>= priority; scan = (scan * percent[file]) / 100; } if (scanning_global_lru(sc)) { zone->lru[l].nr_scan += scan; nr[l] = zone->lru[l].nr_scan; if (nr[l] >= swap_cluster_max) zone->lru[l].nr_scan = 0; else nr[l] = 0; } else nr[l] = scan; } while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || nr[LRU_INACTIVE_FILE]) { for_each_evictable_lru(l) { if (nr[l]) { nr_to_scan = min(nr[l], swap_cluster_max); nr[l] -= nr_to_scan; nr_reclaimed += shrink_list(l, nr_to_scan, zone, sc, priority); } } /* * On large memory systems, scan >> priority can become * really large. This is fine for the starting priority; * we want to put equal scanning pressure on each zone. * However, if the VM has a harder time of freeing pages, * with multiple processes reclaiming pages, the total * freeing target can get unreasonably large. */ if (nr_reclaimed > swap_cluster_max && priority < DEF_PRIORITY && !current_is_kswapd()) break; } sc->nr_reclaimed = nr_reclaimed; /* * Even if we did not try to evict anon pages at all, we want to * rebalance the anon lru active/inactive ratio. */ if (inactive_anon_is_low(zone, sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); throttle_vm_writeout(sc->gfp_mask); } /* * This is the direct reclaim path, for page-allocating processes. We only * try to reclaim pages from zones which will satisfy the caller's allocation * request. * * We reclaim from a zone even if that zone is over pages_high. Because: * a) The caller may be trying to free *extra* pages to satisfy a higher-order * allocation or * b) The zones may be over pages_high but they must go *over* pages_high to * satisfy the `incremental min' zone defense algorithm. * * If a zone is deemed to be full of pinned pages then just give it a light * scan then give up on it. */ static void shrink_zones(int priority, struct zonelist *zonelist, struct scan_control *sc) { enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask); struct zoneref *z; struct zone *zone; sc->all_unreclaimable = 1; for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { if (!populated_zone(zone)) continue; /* * Take care memory controller reclaiming has small influence * to global LRU. */ if (scanning_global_lru(sc)) { if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; note_zone_scanning_priority(zone, priority); if (zone_is_all_unreclaimable(zone) && priority != DEF_PRIORITY) continue; /* Let kswapd poll it */ sc->all_unreclaimable = 0; } else { /* * Ignore cpuset limitation here. We just want to reduce * # of used pages by us regardless of memory shortage. */ sc->all_unreclaimable = 0; mem_cgroup_note_reclaim_priority(sc->mem_cgroup, priority); } shrink_zone(priority, zone, sc); } } /* * This is the main entry point to direct page reclaim. * * If a full scan of the inactive list fails to free enough memory then we * are "out of memory" and something needs to be killed. * * If the caller is !__GFP_FS then the probability of a failure is reasonably * high - the zone may be full of dirty or under-writeback pages, which this * caller can't do much about. We kick pdflush and take explicit naps in the * hope that some of these pages can be written. But if the allocating task * holds filesystem locks which prevent writeout this might not work, and the * allocation attempt will fail. * * returns: 0, if no pages reclaimed * else, the number of pages reclaimed */ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, struct scan_control *sc) { int priority; unsigned long ret = 0; unsigned long total_scanned = 0; struct reclaim_state *reclaim_state = current->reclaim_state; unsigned long lru_pages = 0; struct zoneref *z; struct zone *zone; enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask); delayacct_freepages_start(); if (scanning_global_lru(sc)) count_vm_event(ALLOCSTALL); /* * mem_cgroup will not do shrink_slab. */ if (scanning_global_lru(sc)) { for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; lru_pages += zone_lru_pages(zone); } } for (priority = DEF_PRIORITY; priority >= 0; priority--) { sc->nr_scanned = 0; if (!priority) disable_swap_token(); shrink_zones(priority, zonelist, sc); /* * Don't shrink slabs when reclaiming memory from * over limit cgroups */ if (scanning_global_lru(sc)) { shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages); if (reclaim_state) { sc->nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; } } total_scanned += sc->nr_scanned; if (sc->nr_reclaimed >= sc->swap_cluster_max) { ret = sc->nr_reclaimed; goto out; } /* * Try to write back as many pages as we just scanned. This * tends to cause slow streaming writers to write data to the * disk smoothly, at the dirtying rate, which is nice. But * that's undesirable in laptop mode, where we *want* lumpy * writeout. So in laptop mode, write out the whole world. */ if (total_scanned > sc->swap_cluster_max + sc->swap_cluster_max / 2) { wakeup_pdflush(laptop_mode ? 0 : total_scanned); sc->may_writepage = 1; } /* Take a nap, wait for some writeback to complete */ if (sc->nr_scanned && priority < DEF_PRIORITY - 2) congestion_wait(WRITE, HZ/10); } /* top priority shrink_zones still had more to do? don't OOM, then */ if (!sc->all_unreclaimable && scanning_global_lru(sc)) ret = sc->nr_reclaimed; out: /* * Now that we've scanned all the zones at this priority level, note * that level within the zone so that the next thread which performs * scanning of this zone will immediately start out at this priority * level. This affects only the decision whether or not to bring * mapped pages onto the inactive list. */ if (priority < 0) priority = 0; if (scanning_global_lru(sc)) { for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; zone->prev_priority = priority; } } else mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority); delayacct_freepages_end(); return ret; } unsigned long try_to_free_pages(struct zonelist *zonelist, int order, gfp_t gfp_mask) { struct scan_control sc = { .gfp_mask = gfp_mask, .may_writepage = !laptop_mode, .swap_cluster_max = SWAP_CLUSTER_MAX, .may_swap = 1, .swappiness = vm_swappiness, .order = order, .mem_cgroup = NULL, .isolate_pages = isolate_pages_global, }; return do_try_to_free_pages(zonelist, &sc); } #ifdef CONFIG_CGROUP_MEM_RES_CTLR unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, gfp_t gfp_mask, bool noswap, unsigned int swappiness) { struct scan_control sc = { .may_writepage = !laptop_mode, .may_swap = 1, .swap_cluster_max = SWAP_CLUSTER_MAX, .swappiness = swappiness, .order = 0, .mem_cgroup = mem_cont, .isolate_pages = mem_cgroup_isolate_pages, }; struct zonelist *zonelist; if (noswap) sc.may_swap = 0; sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); zonelist = NODE_DATA(numa_node_id())->node_zonelists; return do_try_to_free_pages(zonelist, &sc); } #endif /* * For kswapd, balance_pgdat() will work across all this node's zones until * they are all at pages_high. * * Returns the number of pages which were actually freed. * * There is special handling here for zones which are full of pinned pages. * This can happen if the pages are all mlocked, or if they are all used by * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. * What we do is to detect the case where all pages in the zone have been * scanned twice and there has been zero successful reclaim. Mark the zone as * dead and from now on, only perform a short scan. Basically we're polling * the zone for when the problem goes away. * * kswapd scans the zones in the highmem->normal->dma direction. It skips * zones which have free_pages > pages_high, but once a zone is found to have * free_pages <= pages_high, we scan that zone and the lower zones regardless * of the number of free pages in the lower zones. This interoperates with * the page allocator fallback scheme to ensure that aging of pages is balanced * across the zones. */ static unsigned long balance_pgdat(pg_data_t *pgdat, int order) { int all_zones_ok; int priority; int i; unsigned long total_scanned; struct reclaim_state *reclaim_state = current->reclaim_state; struct scan_control sc = { .gfp_mask = GFP_KERNEL, .may_swap = 1, .swap_cluster_max = SWAP_CLUSTER_MAX, .swappiness = vm_swappiness, .order = order, .mem_cgroup = NULL, .isolate_pages = isolate_pages_global, }; /* * temp_priority is used to remember the scanning priority at which * this zone was successfully refilled to free_pages == pages_high. */ int temp_priority[MAX_NR_ZONES]; loop_again: total_scanned = 0; sc.nr_reclaimed = 0; sc.may_writepage = !laptop_mode; count_vm_event(PAGEOUTRUN); for (i = 0; i < pgdat->nr_zones; i++) temp_priority[i] = DEF_PRIORITY; for (priority = DEF_PRIORITY; priority >= 0; priority--) { int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ unsigned long lru_pages = 0; /* The swap token gets in the way of swapout... */ if (!priority) disable_swap_token(); all_zones_ok = 1; /* * Scan in the highmem->dma direction for the highest * zone which needs scanning */ for (i = pgdat->nr_zones - 1; i >= 0; i--) { struct zone *zone = pgdat->node_zones + i; if (!populated_zone(zone)) continue; if (zone_is_all_unreclaimable(zone) && priority != DEF_PRIORITY) continue; /* * Do some background aging of the anon list, to give * pages a chance to be referenced before reclaiming. */ if (inactive_anon_is_low(zone, &sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, &sc, priority, 0); if (!zone_watermark_ok(zone, order, zone->pages_high, 0, 0)) { end_zone = i; break; } } if (i < 0) goto out; for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; lru_pages += zone_lru_pages(zone); } /* * Now scan the zone in the dma->highmem direction, stopping * at the last zone which needs scanning. * * We do this because the page allocator works in the opposite * direction. This prevents the page allocator from allocating * pages behind kswapd's direction of progress, which would * cause too much scanning of the lower zones. */ for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; int nr_slab; if (!populated_zone(zone)) continue; if (zone_is_all_unreclaimable(zone) && priority != DEF_PRIORITY) continue; if (!zone_watermark_ok(zone, order, zone->pages_high, end_zone, 0)) all_zones_ok = 0; temp_priority[i] = priority; sc.nr_scanned = 0; note_zone_scanning_priority(zone, priority); /* * We put equal pressure on every zone, unless one * zone has way too many pages free already. */ if (!zone_watermark_ok(zone, order, 8*zone->pages_high, end_zone, 0)) shrink_zone(priority, zone, &sc); reclaim_state->reclaimed_slab = 0; nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages); sc.nr_reclaimed += reclaim_state->reclaimed_slab; total_scanned += sc.nr_scanned; if (zone_is_all_unreclaimable(zone)) continue; if (nr_slab == 0 && zone->pages_scanned >= (zone_lru_pages(zone) * 6)) zone_set_flag(zone, ZONE_ALL_UNRECLAIMABLE); /* * If we've done a decent amount of scanning and * the reclaim ratio is low, start doing writepage * even in laptop mode */ if (total_scanned > SWAP_CLUSTER_MAX * 2 && total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2) sc.may_writepage = 1; } if (all_zones_ok) break; /* kswapd: all done */ /* * OK, kswapd is getting into trouble. Take a nap, then take * another pass across the zones. */ if (total_scanned && priority < DEF_PRIORITY - 2) congestion_wait(WRITE, HZ/10); /* * We do this so kswapd doesn't build up large priorities for * example when it is freeing in parallel with allocators. It * matches the direct reclaim path behaviour in terms of impact * on zone->*_priority. */ if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) break; } out: /* * Note within each zone the priority level at which this zone was * brought into a happy state. So that the next thread which scans this * zone will start out at that priority level. */ for (i = 0; i < pgdat->nr_zones; i++) { struct zone *zone = pgdat->node_zones + i; zone->prev_priority = temp_priority[i]; } if (!all_zones_ok) { cond_resched(); try_to_freeze(); /* * Fragmentation may mean that the system cannot be * rebalanced for high-order allocations in all zones. * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, * it means the zones have been fully scanned and are still * not balanced. For high-order allocations, there is * little point trying all over again as kswapd may * infinite loop. * * Instead, recheck all watermarks at order-0 as they * are the most important. If watermarks are ok, kswapd will go * back to sleep. High-order users can still perform direct * reclaim if they wish. */ if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) order = sc.order = 0; goto loop_again; } return sc.nr_reclaimed; } /* * The background pageout daemon, started as a kernel thread * from the init process. * * This basically trickles out pages so that we have _some_ * free memory available even if there is no other activity * that frees anything up. This is needed for things like routing * etc, where we otherwise might have all activity going on in * asynchronous contexts that cannot page things out. * * If there are applications that are active memory-allocators * (most normal use), this basically shouldn't matter. */ static int kswapd(void *p) { unsigned long order; pg_data_t *pgdat = (pg_data_t*)p; struct task_struct *tsk = current; DEFINE_WAIT(wait); struct reclaim_state reclaim_state = { .reclaimed_slab = 0, }; node_to_cpumask_ptr(cpumask, pgdat->node_id); if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); current->reclaim_state = &reclaim_state; /* * Tell the memory management that we're a "memory allocator", * and that if we need more memory we should get access to it * regardless (see "__alloc_pages()"). "kswapd" should * never get caught in the normal page freeing logic. * * (Kswapd normally doesn't need memory anyway, but sometimes * you need a small amount of memory in order to be able to * page out something else, and this flag essentially protects * us from recursively trying to free more memory as we're * trying to free the first piece of memory in the first place). */ tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; set_freezable(); order = 0; for ( ; ; ) { unsigned long new_order; prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); new_order = pgdat->kswapd_max_order; pgdat->kswapd_max_order = 0; if (order < new_order) { /* * Don't sleep if someone wants a larger 'order' * allocation */ order = new_order; } else { if (!freezing(current)) schedule(); order = pgdat->kswapd_max_order; } finish_wait(&pgdat->kswapd_wait, &wait); if (!try_to_freeze()) { /* We can speed up thawing tasks if we don't call * balance_pgdat after returning from the refrigerator */ balance_pgdat(pgdat, order); } } return 0; } /* * A zone is low on free memory, so wake its kswapd task to service it. */ void wakeup_kswapd(struct zone *zone, int order) { pg_data_t *pgdat; if (!populated_zone(zone)) return; pgdat = zone->zone_pgdat; if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0)) return; if (pgdat->kswapd_max_order < order) pgdat->kswapd_max_order = order; if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) return; if (!waitqueue_active(&pgdat->kswapd_wait)) return; wake_up_interruptible(&pgdat->kswapd_wait); } unsigned long global_lru_pages(void) { return global_page_state(NR_ACTIVE_ANON) + global_page_state(NR_ACTIVE_FILE) + global_page_state(NR_INACTIVE_ANON) + global_page_state(NR_INACTIVE_FILE); } #ifdef CONFIG_PM /* * Helper function for shrink_all_memory(). Tries to reclaim 'nr_pages' pages * from LRU lists system-wide, for given pass and priority, and returns the * number of reclaimed pages * * For pass > 3 we also try to shrink the LRU lists that contain a few pages */ static unsigned long shrink_all_zones(unsigned long nr_pages, int prio, int pass, struct scan_control *sc) { struct zone *zone; unsigned long nr_to_scan, ret = 0; enum lru_list l; for_each_zone(zone) { if (!populated_zone(zone)) continue; if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY) continue; for_each_evictable_lru(l) { /* For pass = 0, we don't shrink the active list */ if (pass == 0 && (l == LRU_ACTIVE || l == LRU_ACTIVE_FILE)) continue; zone->lru[l].nr_scan += (zone_page_state(zone, NR_LRU_BASE + l) >> prio) + 1; if (zone->lru[l].nr_scan >= nr_pages || pass > 3) { zone->lru[l].nr_scan = 0; nr_to_scan = min(nr_pages, zone_page_state(zone, NR_LRU_BASE + l)); ret += shrink_list(l, nr_to_scan, zone, sc, prio); if (ret >= nr_pages) return ret; } } } return ret; } /* * Try to free `nr_pages' of memory, system-wide, and return the number of * freed pages. * * Rather than trying to age LRUs the aim is to preserve the overall * LRU order by reclaiming preferentially * inactive > active > active referenced > active mapped */ unsigned long shrink_all_memory(unsigned long nr_pages) { unsigned long lru_pages, nr_slab; unsigned long ret = 0; int pass; struct reclaim_state reclaim_state; struct scan_control sc = { .gfp_mask = GFP_KERNEL, .may_swap = 0, .swap_cluster_max = nr_pages, .may_writepage = 1, .swappiness = vm_swappiness, .isolate_pages = isolate_pages_global, }; current->reclaim_state = &reclaim_state; lru_pages = global_lru_pages(); nr_slab = global_page_state(NR_SLAB_RECLAIMABLE); /* If slab caches are huge, it's better to hit them first */ while (nr_slab >= lru_pages) { reclaim_state.reclaimed_slab = 0; shrink_slab(nr_pages, sc.gfp_mask, lru_pages); if (!reclaim_state.reclaimed_slab) break; ret += reclaim_state.reclaimed_slab; if (ret >= nr_pages) goto out; nr_slab -= reclaim_state.reclaimed_slab; } /* * We try to shrink LRUs in 5 passes: * 0 = Reclaim from inactive_list only * 1 = Reclaim from active list but don't reclaim mapped * 2 = 2nd pass of type 1 * 3 = Reclaim mapped (normal reclaim) * 4 = 2nd pass of type 3 */ for (pass = 0; pass < 5; pass++) { int prio; /* Force reclaiming mapped pages in the passes #3 and #4 */ if (pass > 2) { sc.may_swap = 1; sc.swappiness = 100; } for (prio = DEF_PRIORITY; prio >= 0; prio--) { unsigned long nr_to_scan = nr_pages - ret; sc.nr_scanned = 0; ret += shrink_all_zones(nr_to_scan, prio, pass, &sc); if (ret >= nr_pages) goto out; reclaim_state.reclaimed_slab = 0; shrink_slab(sc.nr_scanned, sc.gfp_mask, global_lru_pages()); ret += reclaim_state.reclaimed_slab; if (ret >= nr_pages) goto out; if (sc.nr_scanned && prio < DEF_PRIORITY - 2) congestion_wait(WRITE, HZ / 10); } } /* * If ret = 0, we could not shrink LRUs, but there may be something * in slab caches */ if (!ret) { do { reclaim_state.reclaimed_slab = 0; shrink_slab(nr_pages, sc.gfp_mask, global_lru_pages()); ret += reclaim_state.reclaimed_slab; } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0); } out: current->reclaim_state = NULL; return ret; } #endif /* It's optimal to keep kswapds on the same CPUs as their memory, but not required for correctness. So if the last cpu in a node goes away, we get changed to run anywhere: as the first one comes back, restore their cpu bindings. */ static int __devinit cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { int nid; if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { for_each_node_state(nid, N_HIGH_MEMORY) { pg_data_t *pgdat = NODE_DATA(nid); node_to_cpumask_ptr(mask, pgdat->node_id); if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) /* One of our CPUs online: restore mask */ set_cpus_allowed_ptr(pgdat->kswapd, mask); } } return NOTIFY_OK; } /* * This kswapd start function will be called by init and node-hot-add. * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. */ int kswapd_run(int nid) { pg_data_t *pgdat = NODE_DATA(nid); int ret = 0; if (pgdat->kswapd) return 0; pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); if (IS_ERR(pgdat->kswapd)) { /* failure at boot is fatal */ BUG_ON(system_state == SYSTEM_BOOTING); printk("Failed to start kswapd on node %d\n",nid); ret = -1; } return ret; } static int __init kswapd_init(void) { int nid; swap_setup(); for_each_node_state(nid, N_HIGH_MEMORY) kswapd_run(nid); hotcpu_notifier(cpu_callback, 0); return 0; } module_init(kswapd_init) #ifdef CONFIG_NUMA /* * Zone reclaim mode * * If non-zero call zone_reclaim when the number of free pages falls below * the watermarks. */ int zone_reclaim_mode __read_mostly; #define RECLAIM_OFF 0 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ /* * Priority for ZONE_RECLAIM. This determines the fraction of pages * of a node considered for each zone_reclaim. 4 scans 1/16th of * a zone. */ #define ZONE_RECLAIM_PRIORITY 4 /* * Percentage of pages in a zone that must be unmapped for zone_reclaim to * occur. */ int sysctl_min_unmapped_ratio = 1; /* * If the number of slab pages in a zone grows beyond this percentage then * slab reclaim needs to occur. */ int sysctl_min_slab_ratio = 5; /* * Try to free up some pages from this zone through reclaim. */ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { /* Minimum pages needed in order to stay on node */ const unsigned long nr_pages = 1 << order; struct task_struct *p = current; struct reclaim_state reclaim_state; int priority; struct scan_control sc = { .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP), .swap_cluster_max = max_t(unsigned long, nr_pages, SWAP_CLUSTER_MAX), .gfp_mask = gfp_mask, .swappiness = vm_swappiness, .isolate_pages = isolate_pages_global, }; unsigned long slab_reclaimable; disable_swap_token(); cond_resched(); /* * We need to be able to allocate from the reserves for RECLAIM_SWAP * and we also need to be able to write out pages for RECLAIM_WRITE * and RECLAIM_SWAP. */ p->flags |= PF_MEMALLOC | PF_SWAPWRITE; reclaim_state.reclaimed_slab = 0; p->reclaim_state = &reclaim_state; if (zone_page_state(zone, NR_FILE_PAGES) - zone_page_state(zone, NR_FILE_MAPPED) > zone->min_unmapped_pages) { /* * Free memory by calling shrink zone with increasing * priorities until we have enough memory freed. */ priority = ZONE_RECLAIM_PRIORITY; do { note_zone_scanning_priority(zone, priority); shrink_zone(priority, zone, &sc); priority--; } while (priority >= 0 && sc.nr_reclaimed < nr_pages); } slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE); if (slab_reclaimable > zone->min_slab_pages) { /* * shrink_slab() does not currently allow us to determine how * many pages were freed in this zone. So we take the current * number of slab pages and shake the slab until it is reduced * by the same nr_pages that we used for reclaiming unmapped * pages. * * Note that shrink_slab will free memory on all zones and may * take a long time. */ while (shrink_slab(sc.nr_scanned, gfp_mask, order) && zone_page_state(zone, NR_SLAB_RECLAIMABLE) > slab_reclaimable - nr_pages) ; /* * Update nr_reclaimed by the number of slab pages we * reclaimed from this zone. */ sc.nr_reclaimed += slab_reclaimable - zone_page_state(zone, NR_SLAB_RECLAIMABLE); } p->reclaim_state = NULL; current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); return sc.nr_reclaimed >= nr_pages; } int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { int node_id; int ret; /* * Zone reclaim reclaims unmapped file backed pages and * slab pages if we are over the defined limits. * * A small portion of unmapped file backed pages is needed for * file I/O otherwise pages read by file I/O will be immediately * thrown out if the zone is overallocated. So we do not reclaim * if less than a specified percentage of the zone is used by * unmapped file backed pages. */ if (zone_page_state(zone, NR_FILE_PAGES) - zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages && zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) return 0; if (zone_is_all_unreclaimable(zone)) return 0; /* * Do not scan if the allocation should not be delayed. */ if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) return 0; /* * Only run zone reclaim on the local zone or on zones that do not * have associated processors. This will favor the local processor * over remote processors and spread off node memory allocations * as wide as possible. */ node_id = zone_to_nid(zone); if (node_state(node_id, N_CPU) && node_id != numa_node_id()) return 0; if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) return 0; ret = __zone_reclaim(zone, gfp_mask, order); zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); return ret; } #endif #ifdef CONFIG_UNEVICTABLE_LRU /* * page_evictable - test whether a page is evictable * @page: the page to test * @vma: the VMA in which the page is or will be mapped, may be NULL * * Test whether page is evictable--i.e., should be placed on active/inactive * lists vs unevictable list. The vma argument is !NULL when called from the * fault path to determine how to instantate a new page. * * Reasons page might not be evictable: * (1) page's mapping marked unevictable * (2) page is part of an mlocked VMA * */ int page_evictable(struct page *page, struct vm_area_struct *vma) { if (mapping_unevictable(page_mapping(page))) return 0; if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page))) return 0; return 1; } /** * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list * @page: page to check evictability and move to appropriate lru list * @zone: zone page is in * * Checks a page for evictability and moves the page to the appropriate * zone lru list. * * Restrictions: zone->lru_lock must be held, page must be on LRU and must * have PageUnevictable set. */ static void check_move_unevictable_page(struct page *page, struct zone *zone) { VM_BUG_ON(PageActive(page)); retry: ClearPageUnevictable(page); if (page_evictable(page, NULL)) { enum lru_list l = LRU_INACTIVE_ANON + page_is_file_cache(page); __dec_zone_state(zone, NR_UNEVICTABLE); list_move(&page->lru, &zone->lru[l].list); mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l); __inc_zone_state(zone, NR_INACTIVE_ANON + l); __count_vm_event(UNEVICTABLE_PGRESCUED); } else { /* * rotate unevictable list */ SetPageUnevictable(page); list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list); mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE); if (page_evictable(page, NULL)) goto retry; } } /** * scan_mapping_unevictable_pages - scan an address space for evictable pages * @mapping: struct address_space to scan for evictable pages * * Scan all pages in mapping. Check unevictable pages for * evictability and move them to the appropriate zone lru list. */ void scan_mapping_unevictable_pages(struct address_space *mapping) { pgoff_t next = 0; pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; struct zone *zone; struct pagevec pvec; if (mapping->nrpages == 0) return; pagevec_init(&pvec, 0); while (next < end && pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) { int i; int pg_scanned = 0; zone = NULL; for (i = 0; i < pagevec_count(&pvec); i++) { struct page *page = pvec.pages[i]; pgoff_t page_index = page->index; struct zone *pagezone = page_zone(page); pg_scanned++; if (page_index > next) next = page_index; next++; if (pagezone != zone) { if (zone) spin_unlock_irq(&zone->lru_lock); zone = pagezone; spin_lock_irq(&zone->lru_lock); } if (PageLRU(page) && PageUnevictable(page)) check_move_unevictable_page(page, zone); } if (zone) spin_unlock_irq(&zone->lru_lock); pagevec_release(&pvec); count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned); } } /** * scan_zone_unevictable_pages - check unevictable list for evictable pages * @zone - zone of which to scan the unevictable list * * Scan @zone's unevictable LRU lists to check for pages that have become * evictable. Move those that have to @zone's inactive list where they * become candidates for reclaim, unless shrink_inactive_zone() decides * to reactivate them. Pages that are still unevictable are rotated * back onto @zone's unevictable list. */ #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */ static void scan_zone_unevictable_pages(struct zone *zone) { struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list; unsigned long scan; unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE); while (nr_to_scan > 0) { unsigned long batch_size = min(nr_to_scan, SCAN_UNEVICTABLE_BATCH_SIZE); spin_lock_irq(&zone->lru_lock); for (scan = 0; scan < batch_size; scan++) { struct page *page = lru_to_page(l_unevictable); if (!trylock_page(page)) continue; prefetchw_prev_lru_page(page, l_unevictable, flags); if (likely(PageLRU(page) && PageUnevictable(page))) check_move_unevictable_page(page, zone); unlock_page(page); } spin_unlock_irq(&zone->lru_lock); nr_to_scan -= batch_size; } } /** * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages * * A really big hammer: scan all zones' unevictable LRU lists to check for * pages that have become evictable. Move those back to the zones' * inactive list where they become candidates for reclaim. * This occurs when, e.g., we have unswappable pages on the unevictable lists, * and we add swap to the system. As such, it runs in the context of a task * that has possibly/probably made some previously unevictable pages * evictable. */ static void scan_all_zones_unevictable_pages(void) { struct zone *zone; for_each_zone(zone) { scan_zone_unevictable_pages(zone); } } /* * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of * all nodes' unevictable lists for evictable pages */ unsigned long scan_unevictable_pages; int scan_unevictable_handler(struct ctl_table *table, int write, struct file *file, void __user *buffer, size_t *length, loff_t *ppos) { proc_doulongvec_minmax(table, write, file, buffer, length, ppos); if (write && *(unsigned long *)table->data) scan_all_zones_unevictable_pages(); scan_unevictable_pages = 0; return 0; } /* * per node 'scan_unevictable_pages' attribute. On demand re-scan of * a specified node's per zone unevictable lists for evictable pages. */ static ssize_t read_scan_unevictable_node(struct sys_device *dev, struct sysdev_attribute *attr, char *buf) { return sprintf(buf, "0\n"); /* always zero; should fit... */ } static ssize_t write_scan_unevictable_node(struct sys_device *dev, struct sysdev_attribute *attr, const char *buf, size_t count) { struct zone *node_zones = NODE_DATA(dev->id)->node_zones; struct zone *zone; unsigned long res; unsigned long req = strict_strtoul(buf, 10, &res); if (!req) return 1; /* zero is no-op */ for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) { if (!populated_zone(zone)) continue; scan_zone_unevictable_pages(zone); } return 1; } static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, read_scan_unevictable_node, write_scan_unevictable_node); int scan_unevictable_register_node(struct node *node) { return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages); } void scan_unevictable_unregister_node(struct node *node) { sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages); } #endif