The patch titled
mm: tracking shared dirty pages (update)
has been added to the -mm tree. Its filename is
mm-tracking-shared-dirty-pages-update.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: mm: tracking shared dirty pages (update)
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
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
fudges the last condition.
Cleaning the pages on write-back is done with page_mkclean() a new
rmap call. It cleans and wrprotects all PTEs of dirty accountable
pages.
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.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Hugh Dickins <hugh@veritas
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/linux/mm.h | 15 +++++----------
mm/mmap.c | 2 +-
mm/mprotect.c | 9 +++++----
mm/rmap.c | 13 ++++++-------
4 files changed, 17 insertions(+), 22 deletions(-)
diff -puN include/linux/mm.h~mm-tracking-shared-dirty-pages-update include/linux/mm.h
--- a/include/linux/mm.h~mm-tracking-shared-dirty-pages-update
+++ a/include/linux/mm.h
@@ -809,16 +809,13 @@ struct shrinker;
extern struct shrinker *set_shrinker(int, shrinker_t);
extern void remove_shrinker(struct shrinker *shrinker);
-#define VM_NOTIFY_NO_PROT 0x01
-#define VM_NOTIFY_NO_MKWRITE 0x02
-
/*
* 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, int flags)
+static inline int vma_wants_writenotify(struct vm_area_struct *vma)
{
unsigned int vm_flags = vma->vm_flags;
@@ -827,15 +824,13 @@ static inline int vma_wants_writenotify(
return 0;
/* The backer wishes to know when pages are first written to? */
- if (!(flags & VM_NOTIFY_NO_MKWRITE) &&
- vma->vm_ops && vma->vm_ops->page_mkwrite)
+ if (vma->vm_ops && vma->vm_ops->page_mkwrite)
return 1;
/* The open routine did something to the protections already? */
- if (!(flags & VM_NOTIFY_NO_PROT) &&
- pgprot_val(vma->vm_page_prot) !=
- pgprot_val(protection_map[vm_flags &
- (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]))
+ 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? */
diff -puN mm/mmap.c~mm-tracking-shared-dirty-pages-update mm/mmap.c
--- a/mm/mmap.c~mm-tracking-shared-dirty-pages-update
+++ a/mm/mmap.c
@@ -1107,7 +1107,7 @@ munmap_back:
pgoff = vma->vm_pgoff;
vm_flags = vma->vm_flags;
- if (vma_wants_writenotify(vma, 0))
+ if (vma_wants_writenotify(vma))
vma->vm_page_prot =
protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC)];
diff -puN mm/mprotect.c~mm-tracking-shared-dirty-pages-update mm/mprotect.c
--- a/mm/mprotect.c~mm-tracking-shared-dirty-pages-update
+++ a/mm/mprotect.c
@@ -123,7 +123,6 @@ mprotect_fixup(struct vm_area_struct *vm
unsigned long oldflags = vma->vm_flags;
long nrpages = (end - start) >> PAGE_SHIFT;
unsigned long charged = 0;
- unsigned long mask = VM_READ|VM_WRITE|VM_EXEC|VM_SHARED;
pgoff_t pgoff;
int error;
@@ -180,9 +179,11 @@ success:
* held in write mode.
*/
vma->vm_flags = newflags;
- if (vma_wants_writenotify(vma, VM_NOTIFY_NO_PROT))
- mask &= ~VM_SHARED;
- vma->vm_page_prot = protection_map[newflags & mask];
+ vma->vm_page_prot = protection_map[newflags &
+ (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
+ if (vma_wants_writenotify(vma))
+ vma->vm_page_prot = protection_map[newflags &
+ (VM_READ|VM_WRITE|VM_EXEC)];
if (is_vm_hugetlb_page(vma))
hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
diff -puN mm/rmap.c~mm-tracking-shared-dirty-pages-update mm/rmap.c
--- a/mm/rmap.c~mm-tracking-shared-dirty-pages-update
+++ a/mm/rmap.c
@@ -440,8 +440,6 @@ static int page_mkclean_one(struct page
unsigned long address;
pte_t *pte, entry;
spinlock_t *ptl;
- int writefault = vma_wants_writenotify(vma,
- VM_NOTIFY_NO_PROT|VM_NOTIFY_NO_MKWRITE);
int ret = 0;
address = vma_address(page, vma);
@@ -452,13 +450,12 @@ static int page_mkclean_one(struct page
if (!pte)
goto out;
- if (!(pte_dirty(*pte) || (writefault && pte_write(*pte))))
+ if (!pte_dirty(*pte) && !pte_write(*pte))
goto unlock;
entry = ptep_get_and_clear(mm, address, pte);
entry = pte_mkclean(entry);
- if (writefault)
- entry = pte_wrprotect(entry);
+ entry = pte_wrprotect(entry);
ptep_establish(vma, address, pte, entry);
lazy_mmu_prot_update(entry);
ret = 1;
@@ -479,8 +476,10 @@ static int page_mkclean_file(struct addr
BUG_ON(PageAnon(page));
spin_lock(&mapping->i_mmap_lock);
- vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff)
- ret += page_mkclean_one(page, vma);
+ 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;
}
_
Patches currently in -mm which might be from a.p.zijlstra@xxxxxxxxx are
origin.patch
mm-tracking-shared-dirty-pages.patch
mm-tracking-shared-dirty-pages-update.patch
mm-balance-dirty-pages.patch
mm-msync-cleanup.patch
mm-optimize-the-new-mprotect-code-a-bit.patch
mm-small-cleanup-of-install_page.patch
mm-tracking-shared-dirty-pages-checks.patch
mm-tracking-shared-dirty-pages-wimp.patch
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