/* * mm/rmap.c - physical to virtual reverse mappings * * Copyright 2001, Rik van Riel <riel@conectiva.com.br> * Released under the General Public License (GPL). * * Simple, low overhead reverse mapping scheme. * Please try to keep this thing as modular as possible. * * Provides methods for unmapping each kind of mapped page: * the anon methods track anonymous pages, and * the file methods track pages belonging to an inode. * * Original design by Rik van Riel <riel@conectiva.com.br> 2001 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004 * Contributions by Hugh Dickins <hugh@veritas.com> 2003, 2004 */ /* * Lock ordering in mm: * * inode->i_mutex (while writing or truncating, not reading or faulting) * inode->i_alloc_sem (vmtruncate_range) * mm->mmap_sem * page->flags PG_locked (lock_page) * mapping->i_mmap_lock * anon_vma->lock * mm->page_table_lock or pte_lock * zone->lru_lock (in mark_page_accessed, isolate_lru_page) * swap_lock (in swap_duplicate, swap_info_get) * mmlist_lock (in mmput, drain_mmlist and others) * mapping->private_lock (in __set_page_dirty_buffers) * inode_lock (in set_page_dirty's __mark_inode_dirty) * sb_lock (within inode_lock in fs/fs-writeback.c) * mapping->tree_lock (widely used, in set_page_dirty, * in arch-dependent flush_dcache_mmap_lock, * within inode_lock in __sync_single_inode) */ #include <linux/mm.h> #include <linux/pagemap.h> #include <linux/swap.h> #include <linux/swapops.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/rmap.h> #include <linux/rcupdate.h> #include <linux/module.h> #include <linux/kallsyms.h> #include <linux/memcontrol.h> #include <linux/mmu_notifier.h> #include <asm/tlbflush.h> #include "internal.h" static struct kmem_cache *anon_vma_cachep; static inline struct anon_vma *anon_vma_alloc(void) { return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); } static inline void anon_vma_free(struct anon_vma *anon_vma) { kmem_cache_free(anon_vma_cachep, anon_vma); } /** * anon_vma_prepare - attach an anon_vma to a memory region * @vma: the memory region in question * * This makes sure the memory mapping described by 'vma' has * an 'anon_vma' attached to it, so that we can associate the * anonymous pages mapped into it with that anon_vma. * * The common case will be that we already have one, but if * if not we either need to find an adjacent mapping that we * can re-use the anon_vma from (very common when the only * reason for splitting a vma has been mprotect()), or we * allocate a new one. * * Anon-vma allocations are very subtle, because we may have * optimistically looked up an anon_vma in page_lock_anon_vma() * and that may actually touch the spinlock even in the newly * allocated vma (it depends on RCU to make sure that the * anon_vma isn't actually destroyed). * * As a result, we need to do proper anon_vma locking even * for the new allocation. At the same time, we do not want * to do any locking for the common case of already having * an anon_vma. * * This must be called with the mmap_sem held for reading. */ int anon_vma_prepare(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; might_sleep(); if (unlikely(!anon_vma)) { struct mm_struct *mm = vma->vm_mm; struct anon_vma *allocated; anon_vma = find_mergeable_anon_vma(vma); allocated = NULL; if (!anon_vma) { anon_vma = anon_vma_alloc(); if (unlikely(!anon_vma)) return -ENOMEM; allocated = anon_vma; } spin_lock(&anon_vma->lock); /* page_table_lock to protect against threads */ spin_lock(&mm->page_table_lock); if (likely(!vma->anon_vma)) { vma->anon_vma = anon_vma; list_add_tail(&vma->anon_vma_node, &anon_vma->head); allocated = NULL; } spin_unlock(&mm->page_table_lock); spin_unlock(&anon_vma->lock); if (unlikely(allocated)) anon_vma_free(allocated); } return 0; } void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next) { BUG_ON(vma->anon_vma != next->anon_vma); list_del(&next->anon_vma_node); } void __anon_vma_link(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; if (anon_vma) list_add_tail(&vma->anon_vma_node, &anon_vma->head); } void anon_vma_link(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; if (anon_vma) { spin_lock(&anon_vma->lock); list_add_tail(&vma->anon_vma_node, &anon_vma->head); spin_unlock(&anon_vma->lock); } } void anon_vma_unlink(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; int empty; if (!anon_vma) return; spin_lock(&anon_vma->lock); list_del(&vma->anon_vma_node); /* We must garbage collect the anon_vma if it's empty */ empty = list_empty(&anon_vma->head); spin_unlock(&anon_vma->lock); if (empty) anon_vma_free(anon_vma); } static void anon_vma_ctor(void *data) { struct anon_vma *anon_vma = data; spin_lock_init(&anon_vma->lock); INIT_LIST_HEAD(&anon_vma->head); } void __init anon_vma_init(void) { anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor); } /* * Getting a lock on a stable anon_vma from a page off the LRU is * tricky: page_lock_anon_vma rely on RCU to guard against the races. */ struct anon_vma *page_lock_anon_vma(struct page *page) { struct anon_vma *anon_vma; unsigned long anon_mapping; rcu_read_lock(); anon_mapping = (unsigned long) page->mapping; if (!(anon_mapping & PAGE_MAPPING_ANON)) goto out; if (!page_mapped(page)) goto out; anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); spin_lock(&anon_vma->lock); return anon_vma; out: rcu_read_unlock(); return NULL; } void page_unlock_anon_vma(struct anon_vma *anon_vma) { spin_unlock(&anon_vma->lock); rcu_read_unlock(); } /* * At what user virtual address is page expected in @vma? * Returns virtual address or -EFAULT if page's index/offset is not * within the range mapped the @vma. */ static inline unsigned long vma_address(struct page *page, struct vm_area_struct *vma) { pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); unsigned long address; address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { /* page should be within @vma mapping range */ return -EFAULT; } return address; } /* * At what user virtual address is page expected in vma? checking that the * page matches the vma: currently only used on anon pages, by unuse_vma; */ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) { if (PageAnon(page)) { if ((void *)vma->anon_vma != (void *)page->mapping - PAGE_MAPPING_ANON) return -EFAULT; } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) { if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping) return -EFAULT; } else return -EFAULT; return vma_address(page, vma); } /* * Check that @page is mapped at @address into @mm. * * If @sync is false, page_check_address may perform a racy check to avoid * the page table lock when the pte is not present (helpful when reclaiming * highly shared pages). * * On success returns with pte mapped and locked. */ pte_t *page_check_address(struct page *page, struct mm_struct *mm, unsigned long address, spinlock_t **ptlp, int sync) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; spinlock_t *ptl; pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return NULL; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return NULL; pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return NULL; pte = pte_offset_map(pmd, address); /* Make a quick check before getting the lock */ if (!sync && !pte_present(*pte)) { pte_unmap(pte); return NULL; } ptl = pte_lockptr(mm, pmd); spin_lock(ptl); if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { *ptlp = ptl; return pte; } pte_unmap_unlock(pte, ptl); return NULL; } /** * page_mapped_in_vma - check whether a page is really mapped in a VMA * @page: the page to test * @vma: the VMA to test * * Returns 1 if the page is mapped into the page tables of the VMA, 0 * if the page is not mapped into the page tables of this VMA. Only * valid for normal file or anonymous VMAs. */ static int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) { unsigned long address; pte_t *pte; spinlock_t *ptl; address = vma_address(page, vma); if (address == -EFAULT) /* out of vma range */ return 0; pte = page_check_address(page, vma->vm_mm, address, &ptl, 1); if (!pte) /* the page is not in this mm */ return 0; pte_unmap_unlock(pte, ptl); return 1; } /* * Subfunctions of page_referenced: page_referenced_one called * repeatedly from either page_referenced_anon or page_referenced_file. */ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, unsigned int *mapcount) { struct mm_struct *mm = vma->vm_mm; unsigned long address; pte_t *pte; spinlock_t *ptl; int referenced = 0; address = vma_address(page, vma); if (address == -EFAULT) goto out; pte = page_check_address(page, mm, address, &ptl, 0); if (!pte) goto out; /* * Don't want to elevate referenced for mlocked page that gets this far, * in order that it progresses to try_to_unmap and is moved to the * unevictable list. */ if (vma->vm_flags & VM_LOCKED) { *mapcount = 1; /* break early from loop */ goto out_unmap; } if (ptep_clear_flush_young_notify(vma, address, pte)) referenced++; /* Pretend the page is referenced if the task has the swap token and is in the middle of a page fault. */ if (mm != current->mm && has_swap_token(mm) && rwsem_is_locked(&mm->mmap_sem)) referenced++; out_unmap: (*mapcount)--; pte_unmap_unlock(pte, ptl); out: return referenced; } static int page_referenced_anon(struct page *page, struct mem_cgroup *mem_cont) { unsigned int mapcount; struct anon_vma *anon_vma; struct vm_area_struct *vma; int referenced = 0; anon_vma = page_lock_anon_vma(page); if (!anon_vma) return referenced; mapcount = page_mapcount(page); list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { /* * If we are reclaiming on behalf of a cgroup, skip * counting on behalf of references from different * cgroups */ if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) continue; referenced += page_referenced_one(page, vma, &mapcount); if (!mapcount) break; } page_unlock_anon_vma(anon_vma); return referenced; } /** * page_referenced_file - referenced check for object-based rmap * @page: the page we're checking references on. * @mem_cont: target memory controller * * For an object-based mapped page, find all the places it is mapped and * check/clear the referenced flag. This is done by following the page->mapping * pointer, then walking the chain of vmas it holds. It returns the number * of references it found. * * This function is only called from page_referenced for object-based pages. */ static int page_referenced_file(struct page *page, struct mem_cgroup *mem_cont) { unsigned int mapcount; struct address_space *mapping = page->mapping; pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int referenced = 0; /* * The caller's checks on page->mapping and !PageAnon have made * sure that this is a file page: the check for page->mapping * excludes the case just before it gets set on an anon page. */ BUG_ON(PageAnon(page)); /* * The page lock not only makes sure that page->mapping cannot * suddenly be NULLified by truncation, it makes sure that the * structure at mapping cannot be freed and reused yet, * so we can safely take mapping->i_mmap_lock. */ BUG_ON(!PageLocked(page)); spin_lock(&mapping->i_mmap_lock); /* * i_mmap_lock does not stabilize mapcount at all, but mapcount * is more likely to be accurate if we note it after spinning. */ mapcount = page_mapcount(page); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { /* * If we are reclaiming on behalf of a cgroup, skip * counting on behalf of references from different * cgroups */ if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) continue; referenced += page_referenced_one(page, vma, &mapcount); if (!mapcount) break; } spin_unlock(&mapping->i_mmap_lock); return referenced; } /** * page_referenced - test if the page was referenced * @page: the page to test * @is_locked: caller holds lock on the page * @mem_cont: target memory controller * * Quick test_and_clear_referenced for all mappings to a page, * returns the number of ptes which referenced the page. */ int page_referenced(struct page *page, int is_locked, struct mem_cgroup *mem_cont) { int referenced = 0; if (TestClearPageReferenced(page)) referenced++; if (page_mapped(page) && page->mapping) { if (PageAnon(page)) referenced += page_referenced_anon(page, mem_cont); else if (is_locked) referenced += page_referenced_file(page, mem_cont); else if (!trylock_page(page)) referenced++; else { if (page->mapping) referenced += page_referenced_file(page, mem_cont); unlock_page(page); } } if (page_test_and_clear_young(page)) referenced++; return referenced; } static int page_mkclean_one(struct page *page, struct vm_area_struct *vma) { struct mm_struct *mm = vma->vm_mm; unsigned long address; pte_t *pte; spinlock_t *ptl; int ret = 0; address = vma_address(page, vma); if (address == -EFAULT) goto out; pte = page_check_address(page, mm, address, &ptl, 1); if (!pte) goto out; if (pte_dirty(*pte) || pte_write(*pte)) { pte_t entry; flush_cache_page(vma, address, pte_pfn(*pte)); entry = ptep_clear_flush_notify(vma, address, pte); entry = pte_wrprotect(entry); entry = pte_mkclean(entry); set_pte_at(mm, address, pte, entry); ret = 1; } pte_unmap_unlock(pte, ptl); out: return ret; } static int page_mkclean_file(struct address_space *mapping, struct page *page) { pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int ret = 0; BUG_ON(PageAnon(page)); spin_lock(&mapping->i_mmap_lock); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { if (vma->vm_flags & VM_SHARED) ret += page_mkclean_one(page, vma); } spin_unlock(&mapping->i_mmap_lock); return ret; } int page_mkclean(struct page *page) { int ret = 0; BUG_ON(!PageLocked(page)); if (page_mapped(page)) { struct address_space *mapping = page_mapping(page); if (mapping) { ret = page_mkclean_file(mapping, page); if (page_test_dirty(page)) { page_clear_dirty(page); ret = 1; } } } return ret; } EXPORT_SYMBOL_GPL(page_mkclean); /** * __page_set_anon_rmap - setup new anonymous rmap * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped */ static void __page_set_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { struct anon_vma *anon_vma = vma->anon_vma; BUG_ON(!anon_vma); anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; page->index = linear_page_index(vma, address); /* * nr_mapped state can be updated without turning off * interrupts because it is not modified via interrupt. */ __inc_zone_page_state(page, NR_ANON_PAGES); } /** * __page_check_anon_rmap - sanity check anonymous rmap addition * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped */ static void __page_check_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { #ifdef CONFIG_DEBUG_VM /* * The page's anon-rmap details (mapping and index) are guaranteed to * be set up correctly at this point. * * We have exclusion against page_add_anon_rmap because the caller * always holds the page locked, except if called from page_dup_rmap, * in which case the page is already known to be setup. * * We have exclusion against page_add_new_anon_rmap because those pages * are initially only visible via the pagetables, and the pte is locked * over the call to page_add_new_anon_rmap. */ struct anon_vma *anon_vma = vma->anon_vma; anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; BUG_ON(page->mapping != (struct address_space *)anon_vma); BUG_ON(page->index != linear_page_index(vma, address)); #endif } /** * page_add_anon_rmap - add pte mapping to an anonymous page * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped * * The caller needs to hold the pte lock and the page must be locked. */ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); if (atomic_inc_and_test(&page->_mapcount)) __page_set_anon_rmap(page, vma, address); else __page_check_anon_rmap(page, vma, address); } /** * page_add_new_anon_rmap - add pte mapping to a new anonymous page * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped * * Same as page_add_anon_rmap but must only be called on *new* pages. * This means the inc-and-test can be bypassed. * Page does not have to be locked. */ void page_add_new_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { BUG_ON(address < vma->vm_start || address >= vma->vm_end); atomic_set(&page->_mapcount, 0); /* elevate count by 1 (starts at -1) */ __page_set_anon_rmap(page, vma, address); } /** * page_add_file_rmap - add pte mapping to a file page * @page: the page to add the mapping to * * The caller needs to hold the pte lock. */ void page_add_file_rmap(struct page *page) { if (atomic_inc_and_test(&page->_mapcount)) __inc_zone_page_state(page, NR_FILE_MAPPED); } #ifdef CONFIG_DEBUG_VM /** * page_dup_rmap - duplicate pte mapping to a page * @page: the page to add the mapping to * @vma: the vm area being duplicated * @address: the user virtual address mapped * * For copy_page_range only: minimal extract from page_add_file_rmap / * page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's * quicker. * * The caller needs to hold the pte lock. */ void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { BUG_ON(page_mapcount(page) == 0); if (PageAnon(page)) __page_check_anon_rmap(page, vma, address); atomic_inc(&page->_mapcount); } #endif /** * page_remove_rmap - take down pte mapping from a page * @page: page to remove mapping from * @vma: the vm area in which the mapping is removed * * The caller needs to hold the pte lock. */ void page_remove_rmap(struct page *page, struct vm_area_struct *vma) { if (atomic_add_negative(-1, &page->_mapcount)) { if (unlikely(page_mapcount(page) < 0)) { printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)\n", page_mapcount(page)); printk (KERN_EMERG " page pfn = %lx\n", page_to_pfn(page)); printk (KERN_EMERG " page->flags = %lx\n", page->flags); printk (KERN_EMERG " page->count = %x\n", page_count(page)); printk (KERN_EMERG " page->mapping = %p\n", page->mapping); print_symbol (KERN_EMERG " vma->vm_ops = %s\n", (unsigned long)vma->vm_ops); if (vma->vm_ops) { print_symbol (KERN_EMERG " vma->vm_ops->fault = %s\n", (unsigned long)vma->vm_ops->fault); } if (vma->vm_file && vma->vm_file->f_op) print_symbol (KERN_EMERG " vma->vm_file->f_op->mmap = %s\n", (unsigned long)vma->vm_file->f_op->mmap); BUG(); } /* * Now that the last pte has gone, s390 must transfer dirty * flag from storage key to struct page. We can usually skip * this if the page is anon, so about to be freed; but perhaps * not if it's in swapcache - there might be another pte slot * containing the swap entry, but page not yet written to swap. */ if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) { page_clear_dirty(page); set_page_dirty(page); } if (PageAnon(page)) mem_cgroup_uncharge_page(page); __dec_zone_page_state(page, PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED); /* * It would be tidy to reset the PageAnon mapping here, * but that might overwrite a racing page_add_anon_rmap * which increments mapcount after us but sets mapping * before us: so leave the reset to free_hot_cold_page, * and remember that it's only reliable while mapped. * Leaving it set also helps swapoff to reinstate ptes * faster for those pages still in swapcache. */ } } /* * Subfunctions of try_to_unmap: try_to_unmap_one called * repeatedly from either try_to_unmap_anon or try_to_unmap_file. */ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, int migration) { struct mm_struct *mm = vma->vm_mm; unsigned long address; pte_t *pte; pte_t pteval; spinlock_t *ptl; int ret = SWAP_AGAIN; address = vma_address(page, vma); if (address == -EFAULT) goto out; pte = page_check_address(page, mm, address, &ptl, 0); if (!pte) goto out; /* * If the page is mlock()d, we cannot swap it out. * If it's recently referenced (perhaps page_referenced * skipped over this mm) then we should reactivate it. */ if (!migration) { if (vma->vm_flags & VM_LOCKED) { ret = SWAP_MLOCK; goto out_unmap; } if (ptep_clear_flush_young_notify(vma, address, pte)) { ret = SWAP_FAIL; goto out_unmap; } } /* Nuke the page table entry. */ flush_cache_page(vma, address, page_to_pfn(page)); pteval = ptep_clear_flush_notify(vma, address, pte); /* Move the dirty bit to the physical page now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); /* Update high watermark before we lower rss */ update_hiwater_rss(mm); if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; if (PageSwapCache(page)) { /* * Store the swap location in the pte. * See handle_pte_fault() ... */ swap_duplicate(entry); if (list_empty(&mm->mmlist)) { spin_lock(&mmlist_lock); if (list_empty(&mm->mmlist)) list_add(&mm->mmlist, &init_mm.mmlist); spin_unlock(&mmlist_lock); } dec_mm_counter(mm, anon_rss); #ifdef CONFIG_MIGRATION } else { /* * Store the pfn of the page in a special migration * pte. do_swap_page() will wait until the migration * pte is removed and then restart fault handling. */ BUG_ON(!migration); entry = make_migration_entry(page, pte_write(pteval)); #endif } set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); BUG_ON(pte_file(*pte)); } else #ifdef CONFIG_MIGRATION if (migration) { /* Establish migration entry for a file page */ swp_entry_t entry; entry = make_migration_entry(page, pte_write(pteval)); set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); } else #endif dec_mm_counter(mm, file_rss); page_remove_rmap(page, vma); page_cache_release(page); out_unmap: pte_unmap_unlock(pte, ptl); out: return ret; } /* * objrmap doesn't work for nonlinear VMAs because the assumption that * offset-into-file correlates with offset-into-virtual-addresses does not hold. * Consequently, given a particular page and its ->index, we cannot locate the * ptes which are mapping that page without an exhaustive linear search. * * So what this code does is a mini "virtual scan" of each nonlinear VMA which * maps the file to which the target page belongs. The ->vm_private_data field * holds the current cursor into that scan. Successive searches will circulate * around the vma's virtual address space. * * So as more replacement pressure is applied to the pages in a nonlinear VMA, * more scanning pressure is placed against them as well. Eventually pages * will become fully unmapped and are eligible for eviction. * * For very sparsely populated VMAs this is a little inefficient - chances are * there there won't be many ptes located within the scan cluster. In this case * maybe we could scan further - to the end of the pte page, perhaps. * * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can * acquire it without blocking. If vma locked, mlock the pages in the cluster, * rather than unmapping them. If we encounter the "check_page" that vmscan is * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN. */ #define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE) #define CLUSTER_MASK (~(CLUSTER_SIZE - 1)) static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, struct vm_area_struct *vma, struct page *check_page) { struct mm_struct *mm = vma->vm_mm; pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; pte_t pteval; spinlock_t *ptl; struct page *page; unsigned long address; unsigned long end; int ret = SWAP_AGAIN; int locked_vma = 0; address = (vma->vm_start + cursor) & CLUSTER_MASK; end = address + CLUSTER_SIZE; if (address < vma->vm_start) address = vma->vm_start; if (end > vma->vm_end) end = vma->vm_end; pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return ret; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return ret; pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return ret; /* * MLOCK_PAGES => feature is configured. * if we can acquire the mmap_sem for read, and vma is VM_LOCKED, * keep the sem while scanning the cluster for mlocking pages. */ if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) { locked_vma = (vma->vm_flags & VM_LOCKED); if (!locked_vma) up_read(&vma->vm_mm->mmap_sem); /* don't need it */ } pte = pte_offset_map_lock(mm, pmd, address, &ptl); /* Update high watermark before we lower rss */ update_hiwater_rss(mm); for (; address < end; pte++, address += PAGE_SIZE) { if (!pte_present(*pte)) continue; page = vm_normal_page(vma, address, *pte); BUG_ON(!page || PageAnon(page)); if (locked_vma) { mlock_vma_page(page); /* no-op if already mlocked */ if (page == check_page) ret = SWAP_MLOCK; continue; /* don't unmap */ } if (ptep_clear_flush_young_notify(vma, address, pte)) continue; /* Nuke the page table entry. */ flush_cache_page(vma, address, pte_pfn(*pte)); pteval = ptep_clear_flush_notify(vma, address, pte); /* If nonlinear, store the file page offset in the pte. */ if (page->index != linear_page_index(vma, address)) set_pte_at(mm, address, pte, pgoff_to_pte(page->index)); /* Move the dirty bit to the physical page now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); page_remove_rmap(page, vma); page_cache_release(page); dec_mm_counter(mm, file_rss); (*mapcount)--; } pte_unmap_unlock(pte - 1, ptl); if (locked_vma) up_read(&vma->vm_mm->mmap_sem); return ret; } /* * common handling for pages mapped in VM_LOCKED vmas */ static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma) { int mlocked = 0; if (down_read_trylock(&vma->vm_mm->mmap_sem)) { if (vma->vm_flags & VM_LOCKED) { mlock_vma_page(page); mlocked++; /* really mlocked the page */ } up_read(&vma->vm_mm->mmap_sem); } return mlocked; } /** * try_to_unmap_anon - unmap or unlock anonymous page using the object-based * rmap method * @page: the page to unmap/unlock * @unlock: request for unlock rather than unmap [unlikely] * @migration: unmapping for migration - ignored if @unlock * * Find all the mappings of a page using the mapping pointer and the vma chains * contained in the anon_vma struct it points to. * * This function is only called from try_to_unmap/try_to_munlock for * anonymous pages. * When called from try_to_munlock(), the mmap_sem of the mm containing the vma * where the page was found will be held for write. So, we won't recheck * vm_flags for that VMA. That should be OK, because that vma shouldn't be * 'LOCKED. */ static int try_to_unmap_anon(struct page *page, int unlock, int migration) { struct anon_vma *anon_vma; struct vm_area_struct *vma; unsigned int mlocked = 0; int ret = SWAP_AGAIN; if (MLOCK_PAGES && unlikely(unlock)) ret = SWAP_SUCCESS; /* default for try_to_munlock() */ anon_vma = page_lock_anon_vma(page); if (!anon_vma) return ret; list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { if (MLOCK_PAGES && unlikely(unlock)) { if (!((vma->vm_flags & VM_LOCKED) && page_mapped_in_vma(page, vma))) continue; /* must visit all unlocked vmas */ ret = SWAP_MLOCK; /* saw at least one mlocked vma */ } else { ret = try_to_unmap_one(page, vma, migration); if (ret == SWAP_FAIL || !page_mapped(page)) break; } if (ret == SWAP_MLOCK) { mlocked = try_to_mlock_page(page, vma); if (mlocked) break; /* stop if actually mlocked page */ } } page_unlock_anon_vma(anon_vma); if (mlocked) ret = SWAP_MLOCK; /* actually mlocked the page */ else if (ret == SWAP_MLOCK) ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ return ret; } /** * try_to_unmap_file - unmap/unlock file page using the object-based rmap method * @page: the page to unmap/unlock * @unlock: request for unlock rather than unmap [unlikely] * @migration: unmapping for migration - ignored if @unlock * * Find all the mappings of a page using the mapping pointer and the vma chains * contained in the address_space struct it points to. * * This function is only called from try_to_unmap/try_to_munlock for * object-based pages. * When called from try_to_munlock(), the mmap_sem of the mm containing the vma * where the page was found will be held for write. So, we won't recheck * vm_flags for that VMA. That should be OK, because that vma shouldn't be * 'LOCKED. */ static int try_to_unmap_file(struct page *page, int unlock, int migration) { struct address_space *mapping = page->mapping; pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int ret = SWAP_AGAIN; unsigned long cursor; unsigned long max_nl_cursor = 0; unsigned long max_nl_size = 0; unsigned int mapcount; unsigned int mlocked = 0; if (MLOCK_PAGES && unlikely(unlock)) ret = SWAP_SUCCESS; /* default for try_to_munlock() */ spin_lock(&mapping->i_mmap_lock); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { if (MLOCK_PAGES && unlikely(unlock)) { if (!(vma->vm_flags & VM_LOCKED)) continue; /* must visit all vmas */ ret = SWAP_MLOCK; } else { ret = try_to_unmap_one(page, vma, migration); if (ret == SWAP_FAIL || !page_mapped(page)) goto out; } if (ret == SWAP_MLOCK) { mlocked = try_to_mlock_page(page, vma); if (mlocked) break; /* stop if actually mlocked page */ } } if (mlocked) goto out; if (list_empty(&mapping->i_mmap_nonlinear)) goto out; list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) { if (MLOCK_PAGES && unlikely(unlock)) { if (!(vma->vm_flags & VM_LOCKED)) continue; /* must visit all vmas */ ret = SWAP_MLOCK; /* leave mlocked == 0 */ goto out; /* no need to look further */ } if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED)) continue; cursor = (unsigned long) vma->vm_private_data; if (cursor > max_nl_cursor) max_nl_cursor = cursor; cursor = vma->vm_end - vma->vm_start; if (cursor > max_nl_size) max_nl_size = cursor; } if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */ ret = SWAP_FAIL; goto out; } /* * We don't try to search for this page in the nonlinear vmas, * and page_referenced wouldn't have found it anyway. Instead * just walk the nonlinear vmas trying to age and unmap some. * The mapcount of the page we came in with is irrelevant, * but even so use it as a guide to how hard we should try? */ mapcount = page_mapcount(page); if (!mapcount) goto out; cond_resched_lock(&mapping->i_mmap_lock); max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK; if (max_nl_cursor == 0) max_nl_cursor = CLUSTER_SIZE; do { list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) { if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED)) continue; cursor = (unsigned long) vma->vm_private_data; while ( cursor < max_nl_cursor && cursor < vma->vm_end - vma->vm_start) { ret = try_to_unmap_cluster(cursor, &mapcount, vma, page); if (ret == SWAP_MLOCK) mlocked = 2; /* to return below */ cursor += CLUSTER_SIZE; vma->vm_private_data = (void *) cursor; if ((int)mapcount <= 0) goto out; } vma->vm_private_data = (void *) max_nl_cursor; } cond_resched_lock(&mapping->i_mmap_lock); max_nl_cursor += CLUSTER_SIZE; } while (max_nl_cursor <= max_nl_size); /* * Don't loop forever (perhaps all the remaining pages are * in locked vmas). Reset cursor on all unreserved nonlinear * vmas, now forgetting on which ones it had fallen behind. */ list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) vma->vm_private_data = NULL; out: spin_unlock(&mapping->i_mmap_lock); if (mlocked) ret = SWAP_MLOCK; /* actually mlocked the page */ else if (ret == SWAP_MLOCK) ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ return ret; } /** * try_to_unmap - try to remove all page table mappings to a page * @page: the page to get unmapped * @migration: migration flag * * Tries to remove all the page table entries which are mapping this * page, used in the pageout path. Caller must hold the page lock. * Return values are: * * SWAP_SUCCESS - we succeeded in removing all mappings * SWAP_AGAIN - we missed a mapping, try again later * SWAP_FAIL - the page is unswappable * SWAP_MLOCK - page is mlocked. */ int try_to_unmap(struct page *page, int migration) { int ret; BUG_ON(!PageLocked(page)); if (PageAnon(page)) ret = try_to_unmap_anon(page, 0, migration); else ret = try_to_unmap_file(page, 0, migration); if (ret != SWAP_MLOCK && !page_mapped(page)) ret = SWAP_SUCCESS; return ret; } #ifdef CONFIG_UNEVICTABLE_LRU /** * try_to_munlock - try to munlock a page * @page: the page to be munlocked * * Called from munlock code. Checks all of the VMAs mapping the page * to make sure nobody else has this page mlocked. The page will be * returned with PG_mlocked cleared if no other vmas have it mlocked. * * Return values are: * * SWAP_SUCCESS - no vma's holding page mlocked. * SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem * SWAP_MLOCK - page is now mlocked. */ int try_to_munlock(struct page *page) { VM_BUG_ON(!PageLocked(page) || PageLRU(page)); if (PageAnon(page)) return try_to_unmap_anon(page, 1, 0); else return try_to_unmap_file(page, 1, 0); } #endif