Commit af34770e authored Feb 22, 2013 by Johannes Weiner Committed by Linus Torvalds Feb 23, 2013

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>

parent 9b4f98cd

mm/ksm.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -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;

mm/memory.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -3044,6 +3044,9 @@ 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);
		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);

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