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Commit af34770e authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarHugh 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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);