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Commit bdf4f4d2 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

mm: memcg: only check anon swapin page charges for swap cache 



shmem knows for sure that the page is in swap cache when attempting to
charge a page, because the cache charge entry function has a check for it.
Only anon pages may be removed from swap cache already when trying to
charge their swapin.

Adjust the comment, though: '4969c119 mm: fix swapin race condition' added
a stable PageSwapCache check under the page lock in the do_swap_page()
before calling the memory controller, so it's unuse_pte()'s pte_same()
that may fail.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Wanpeng Li <liwp.linux@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 90deb788

mm/memcontrol.c

+14 −8
Original line number Diff line number Diff line
@@ -2818,14 +2818,6 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm, 
		return 0;

	if (!do_swap_account)

		goto charge_cur_mm;

	/*

	 * A racing thread's fault, or swapoff, may have already updated

	 * the pte, and even removed page from swap cache: in those cases

	 * do_swap_page()'s pte_same() test will fail; but there's also a

	 * KSM case which does need to charge the page.

	 */

	if (!PageSwapCache(page))

		goto charge_cur_mm;

	memcg = try_get_mem_cgroup_from_page(page);

	if (!memcg)

		goto charge_cur_mm;
@@ -2848,6 +2840,20 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page, 
	*memcgp = NULL;

	if (mem_cgroup_disabled())

		return 0;

	/*

	 * A racing thread's fault, or swapoff, may have already

	 * updated the pte, and even removed page from swap cache: in

	 * those cases unuse_pte()'s pte_same() test will fail; but

	 * there's also a KSM case which does need to charge the page.

	 */

	if (!PageSwapCache(page)) {

		int ret;



		ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);

		if (ret == -EINTR)

			ret = 0;

		return ret;

	}

	return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);

}