linux-kernel - [patch 11/11] mm: memcg: only check anon swapin page charges for swap cache

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Date:	Thu,  5 Jul 2012 02:45:03 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [patch 11/11] 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: '4969c11 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: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c |   22 ++++++++++++++--------
 1 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d3701cd..9b7e256 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2751,14 +2751,6 @@ 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;
@@ -2781,6 +2773,20 @@ 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);
 }
 
-- 
1.7.7.6

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