The patch titled
ksm: remove redundancies when merging page
has been added to the -mm tree. Its filename is
ksm-remove-redundancies-when-merging-page.patch
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------------------------------------------------------
Subject: ksm: remove redundancies when merging page
From: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
There is no need for replace_page() to calculate a write-protected prot
vm_page_prot must already be write-protected for an anonymous page (see
mm/memory.c do_anonymous_page() for similar reliance on vm_page_prot).
There is no need for try_to_merge_one_page() to get_page and put_page on
newpage and oldpage: in every case we already hold a reference to each of
them.
But some instinct makes me move try_to_merge_one_page()'s unlock_page of
oldpage down after replace_page(): that doesn't increase contention on the
ksm page, and makes thinking about the transition easier.
Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Cc: Izik Eidus <ieidus@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 26 ++++++--------------------
1 file changed, 6 insertions(+), 20 deletions(-)
diff -puN mm/ksm.c~ksm-remove-redundancies-when-merging-page mm/ksm.c
--- a/mm/ksm.c~ksm-remove-redundancies-when-merging-page
+++ a/mm/ksm.c
@@ -647,7 +647,7 @@ static int write_protect_page(struct vm_
* Check that no O_DIRECT or similar I/O is in progress on the
* page
*/
- if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
+ if (page_mapcount(page) + 1 + swapped != page_count(page)) {
set_pte_at_notify(mm, addr, ptep, entry);
goto out_unlock;
}
@@ -682,11 +682,8 @@ static int replace_page(struct vm_area_s
pte_t *ptep;
spinlock_t *ptl;
unsigned long addr;
- pgprot_t prot;
int err = -EFAULT;
- prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
-
addr = page_address_in_vma(oldpage, vma);
if (addr == -EFAULT)
goto out;
@@ -714,7 +711,7 @@ static int replace_page(struct vm_area_s
flush_cache_page(vma, addr, pte_pfn(*ptep));
ptep_clear_flush(vma, addr, ptep);
- set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
+ set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, vma->vm_page_prot));
page_remove_rmap(oldpage);
put_page(oldpage);
@@ -746,13 +743,9 @@ static int try_to_merge_one_page(struct
if (!(vma->vm_flags & VM_MERGEABLE))
goto out;
-
if (!PageAnon(oldpage))
goto out;
- get_page(newpage);
- get_page(oldpage);
-
/*
* We need the page lock to read a stable PageSwapCache in
* write_protect_page(). We use trylock_page() instead of
@@ -761,25 +754,18 @@ static int try_to_merge_one_page(struct
* then come back to this page when it is unlocked.
*/
if (!trylock_page(oldpage))
- goto out_putpage;
+ goto out;
/*
* If this anonymous page is mapped only here, its pte may need
* to be write-protected. If it's mapped elsewhere, all of its
* ptes are necessarily already write-protected. But in either
* case, we need to lock and check page_count is not raised.
*/
- if (write_protect_page(vma, oldpage, &orig_pte)) {
- unlock_page(oldpage);
- goto out_putpage;
- }
- unlock_page(oldpage);
-
- if (pages_identical(oldpage, newpage))
+ if (write_protect_page(vma, oldpage, &orig_pte) == 0 &&
+ pages_identical(oldpage, newpage))
err = replace_page(vma, oldpage, newpage, orig_pte);
-out_putpage:
- put_page(oldpage);
- put_page(newpage);
+ unlock_page(oldpage);
out:
return err;
}
_
Patches currently in -mm which might be from hugh.dickins@xxxxxxxxxxxxx are
mmap-dont-return-enomem-when-mapcount-is-temporarily-exceeded-in-munmap.patch
mmap-dont-return-enomem-when-mapcount-is-temporarily-exceeded-in-munmap-checkpatch-fixes.patch
vmalloc-adjust-gfp-mask-passed-on-nested-vmalloc-invocation.patch
swap_info-private-to-swapfilec.patch
swap_info-change-to-array-of-pointers.patch
swap_info-include-first_swap_extent.patch
swap_info-include-first_swap_extent-fix.patch
swap_info-include-first_swap_extent-fix-fix.patch
swap_info-miscellaneous-minor-cleanups.patch
swap_info-swap_has_cache-cleanups.patch
swap_info-swap_map-of-chars-not-shorts.patch
swap_info-swap-count-continuations.patch
swap_info-note-swap_map_shmem.patch
swap_info-reorder-its-fields.patch
rmap-fix-the-comment-for-try_to_unmap_anon.patch
oom_kill-use-rss-value-instead-of-vm-size-for-badness.patch
mm-define-page_mapping_flags.patch
mm-mlocking-in-try_to_unmap_one.patch
mm-config_mmu-for-pg_mlocked.patch
mm-pass-address-down-to-rmap-ones.patch
mm-stop-ptlock-enlarging-struct-page.patch
mm-sigbus-instead-of-abusing-oom.patch
ksm-three-remove_rmap_item_from_tree-cleanups.patch
ksm-remove-redundancies-when-merging-page.patch
ksm-cleanup-some-function-arguments.patch
ksm-singly-linked-rmap_list.patch
ksm-separate-stable_node.patch
ksm-stable_node-point-to-page-and-back.patch
elf-kill-use_elf_core_dump.patch
prio_tree-debugging-patch.patch
--
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