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[PATCH] do_wp_page: cannot share file page

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A small optimization to do_wp_page's check for whether to avoid copy by
reusing the page already mapped.  It can never share a cached file page,
nor can it share a reserved page (often the empty zero page), so it's a
waste of time to lock and unlock in those cases.  Which nowadays can both
be neatly excluded by a preliminary PageAnon test.

Christoph has reported that a preliminary page_count test proved valuable
for scalability here, but PageAnon covers more common cases all at once.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins 2005-06-21 17:15:11 -07:00 committed by Linus Torvalds
parent 08ef472937
commit d296e9cd02
1 changed files with 1 additions and 1 deletions
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2
mm/memory.c
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@ -1239,7 +1239,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
}
old_page = pfn_to_page(pfn);
if (!TestSetPageLocked(old_page)) {
if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
int reuse = can_share_swap_page(old_page);
unlock_page(old_page);
if (reuse) {