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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2006-09-25 23:30:57 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-26 08:48:44 -0700
commitd08b3851da41d0ee60851f2c75b118e1f7a5fc89 (patch)
treea01f6930a1387e8f66607e2fe16c62bb7044353b /include
parent725d704ecaca4a43f067092c140d4f3271cf2856 (diff)
[PATCH] mm: tracking shared dirty pages
Tracking of dirty pages in shared writeable mmap()s. The idea is simple: write protect clean shared writeable pages, catch the write-fault, make writeable and set dirty. On page write-back clean all the PTE dirty bits and write protect them once again. The implementation is a tad harder, mainly because the default backing_dev_info capabilities were too loosely maintained. Hence it is not enough to test the backing_dev_info for cap_account_dirty. The current heuristic is as follows, a VMA is eligible when: - its shared writeable (vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED) - it is not a 'special' mapping (vm_flags & (VM_PFNMAP|VM_INSERTPAGE)) == 0 - the backing_dev_info is cap_account_dirty mapping_cap_account_dirty(vma->vm_file->f_mapping) - f_op->mmap() didn't change the default page protection Page from remap_pfn_range() are explicitly excluded because their COW semantics are already horrid enough (see vm_normal_page() in do_wp_page()) and because they don't have a backing store anyway. mprotect() is taught about the new behaviour as well. However it overrides the last condition. Cleaning the pages on write-back is done with page_mkclean() a new rmap call. It can be called on any page, but is currently only implemented for mapped pages, if the page is found the be of a VMA that accounts dirty pages it will also wrprotect the PTE. Finally, in fs/buffers.c:try_to_free_buffers(); remove clear_page_dirty() from under ->private_lock. This seems to be safe, since ->private_lock is used to serialize access to the buffers, not the page itself. This is needed because clear_page_dirty() will call into page_mkclean() and would thereby violate locking order. [dhowells@redhat.com: Provide a page_mkclean() implementation for NOMMU] Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Hugh Dickins <hugh@veritas.com> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mm.h34
-rw-r--r--include/linux/rmap.h14
2 files changed, 48 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7d20b25c58f..449841413cf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -15,6 +15,7 @@
#include <linux/fs.h>
#include <linux/mutex.h>
#include <linux/debug_locks.h>
+#include <linux/backing-dev.h>
struct mempolicy;
struct anon_vma;
@@ -810,6 +811,39 @@ struct shrinker;
extern struct shrinker *set_shrinker(int, shrinker_t);
extern void remove_shrinker(struct shrinker *shrinker);
+/*
+ * Some shared mappigns will want the pages marked read-only
+ * to track write events. If so, we'll downgrade vm_page_prot
+ * to the private version (using protection_map[] without the
+ * VM_SHARED bit).
+ */
+static inline int vma_wants_writenotify(struct vm_area_struct *vma)
+{
+ unsigned int vm_flags = vma->vm_flags;
+
+ /* If it was private or non-writable, the write bit is already clear */
+ if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
+ return 0;
+
+ /* The backer wishes to know when pages are first written to? */
+ if (vma->vm_ops && vma->vm_ops->page_mkwrite)
+ return 1;
+
+ /* The open routine did something to the protections already? */
+ if (pgprot_val(vma->vm_page_prot) !=
+ pgprot_val(protection_map[vm_flags &
+ (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]))
+ return 0;
+
+ /* Specialty mapping? */
+ if (vm_flags & (VM_PFNMAP|VM_INSERTPAGE))
+ return 0;
+
+ /* Can the mapping track the dirty pages? */
+ return vma->vm_file && vma->vm_file->f_mapping &&
+ mapping_cap_account_dirty(vma->vm_file->f_mapping);
+}
+
extern pte_t *FASTCALL(get_locked_pte(struct mm_struct *mm, unsigned long addr, spinlock_t **ptl));
int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bf97b090001..db2c1df4fef 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -103,6 +103,14 @@ pte_t *page_check_address(struct page *, struct mm_struct *,
*/
unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
+/*
+ * Cleans the PTEs of shared mappings.
+ * (and since clean PTEs should also be readonly, write protects them too)
+ *
+ * returns the number of cleaned PTEs.
+ */
+int page_mkclean(struct page *);
+
#else /* !CONFIG_MMU */
#define anon_vma_init() do {} while (0)
@@ -112,6 +120,12 @@ unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
#define page_referenced(page,l) TestClearPageReferenced(page)
#define try_to_unmap(page, refs) SWAP_FAIL
+static inline int page_mkclean(struct page *page)
+{
+ return 0;
+}
+
+
#endif /* CONFIG_MMU */
/*