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mm: reduce rmap overhead for ex-KSM page copies created on swap faults 

When ex-KSM pages are faulted from swap cache, the fault handler is not
capable of re-establishing anon_vma-spanning KSM pages.  In this case, a
copy of the page is created instead, just like during a COW break.

These freshly made copies are known to be exclusive to the faulting VMA
and there is no reason to go look for this page in parent and sibling
processes during rmap operations.

Use page_add_new_anon_rmap() for these copies.  This also puts them on
the proper LRU lists and marks them SwapBacked, so we can get rid of
doing this ad-hoc in the KSM copy code.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Satoru Moriya <satoru.moriya@hds.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2013-02-22 16:32:20 -08:00 committed by Linus Torvalds
parent 9b4f98cdac
commit af34770e55
2 changed files with 4 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
mm/ksm.c
View File

@ -1590,13 +1590,7 @@ struct page *ksm_does_need_to_copy(struct page *page,
SetPageDirty(new_page);
__SetPageUptodate(new_page);
SetPageSwapBacked(new_page);
__set_page_locked(new_page);
if (!mlocked_vma_newpage(vma, new_page))
lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
else
add_page_to_unevictable_list(new_page);
}
return new_page;

5
mm/memory.c
View File

@ -3044,7 +3044,10 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
}
flush_icache_page(vma, page);
set_pte_at(mm, address, page_table, pte);
do_page_add_anon_rmap(page, vma, address, exclusive);
if (swapcache) /* ksm created a completely new copy */
page_add_new_anon_rmap(page, vma, address);
else
do_page_add_anon_rmap(page, vma, address, exclusive);
/* It's better to call commit-charge after rmap is established */
mem_cgroup_commit_charge_swapin(page, ptr);