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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2006-09-26 02:30:57 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-26 11:48:44 -0400
commitd08b3851da41d0ee60851f2c75b118e1f7a5fc89 (patch)
treea01f6930a1387e8f66607e2fe16c62bb7044353b /mm/mprotect.c
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 'mm/mprotect.c')
-rw-r--r--mm/mprotect.c21
1 files changed, 8 insertions, 13 deletions
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 638edabaff7..367b7f6c063 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -123,8 +123,6 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
123 unsigned long oldflags = vma->vm_flags; 123 unsigned long oldflags = vma->vm_flags;
124 long nrpages = (end - start) >> PAGE_SHIFT; 124 long nrpages = (end - start) >> PAGE_SHIFT;
125 unsigned long charged = 0; 125 unsigned long charged = 0;
126 unsigned int mask;
127 pgprot_t newprot;
128 pgoff_t pgoff; 126 pgoff_t pgoff;
129 int error; 127 int error;
130 128
@@ -176,24 +174,21 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
176 } 174 }
177 175
178success: 176success:
179 /* Don't make the VMA automatically writable if it's shared, but the
180 * backer wishes to know when pages are first written to */
181 mask = VM_READ|VM_WRITE|VM_EXEC|VM_SHARED;
182 if (vma->vm_ops && vma->vm_ops->page_mkwrite)
183 mask &= ~VM_SHARED;
184
185 newprot = protection_map[newflags & mask];
186
187 /* 177 /*
188 * vm_flags and vm_page_prot are protected by the mmap_sem 178 * vm_flags and vm_page_prot are protected by the mmap_sem
189 * held in write mode. 179 * held in write mode.
190 */ 180 */
191 vma->vm_flags = newflags; 181 vma->vm_flags = newflags;
192 vma->vm_page_prot = newprot; 182 vma->vm_page_prot = protection_map[newflags &
183 (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
184 if (vma_wants_writenotify(vma))
185 vma->vm_page_prot = protection_map[newflags &
186 (VM_READ|VM_WRITE|VM_EXEC)];
187
193 if (is_vm_hugetlb_page(vma)) 188 if (is_vm_hugetlb_page(vma))
194 hugetlb_change_protection(vma, start, end, newprot); 189 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
195 else 190 else
196 change_protection(vma, start, end, newprot); 191 change_protection(vma, start, end, vma->vm_page_prot);
197 vm_stat_account(mm, oldflags, vma->vm_file, -nrpages); 192 vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
198 vm_stat_account(mm, newflags, vma->vm_file, nrpages); 193 vm_stat_account(mm, newflags, vma->vm_file, nrpages);
199 return 0; 194 return 0;