linux-kernel - [PATCH -mm] memcg: fix handling of shmem migration(v2)

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Date:	Wed, 17 Sep 2008 16:55:44 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	nishimura@....nes.nec.co.jp, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	balbir@...ux.vnet.ibm.com, xemul@...nvz.org
Subject: [PATCH -mm] memcg: fix handling of shmem migration(v2)

Before this patch, if migrating shmem/tmpfs pages, newpage would be
charged with PAGE_CGROUP_FLAG_FILE set, while oldpage has been charged
without the flag.

The problem here is mem_cgroup_move_lists doesn't clear(or set)
the PAGE_CGROUP_FLAG_FILE flag, so pc->flags of the newpage
remains PAGE_CGROUP_FLAG_FILE set even when the pc is moved to
another lru(anon) by mem_cgroup_move_lists. And this leads to
incorrect MEM_CGROUP_ZSTAT.
(In my test, I see an underflow of MEM_CGROUP_ZSTAT(active_file).
As a result, mem_cgroup_calc_reclaim returns very huge number and
causes soft lockup on page reclaim.)

I'm not sure if mem_cgroup_move_lists should handle PAGE_CGROUP_FLAG_FILE
or not(I suppose it should be used to move between active <-> inactive,
not anon <-> file), I added MEM_CGROUP_CHARGE_TYPE_SHMEM for precharge
at shmem's page migration.


ChangeLog: v1->v2
- instead of modifying migrate.c, modify memcontrol.c only.
- add MEM_CGROUP_CHARGE_TYPE_SHMEM.


Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
---
 mm/memcontrol.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2979d22..ef8812d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -179,6 +179,7 @@ enum charge_type {
 	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
 	MEM_CGROUP_CHARGE_TYPE_MAPPED,
 	MEM_CGROUP_CHARGE_TYPE_FORCE,	/* used by force_empty */
+	MEM_CGROUP_CHARGE_TYPE_SHMEM,	/* used by page migration of shmem */
 };
 
 /*
@@ -579,8 +580,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 			pc->flags |= PAGE_CGROUP_FLAG_FILE;
 		else
 			pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
-	} else
+	} else if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
 		pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
+	else /* MEM_CGROUP_CHARGE_TYPE_SHMEM */
+		pc->flags = PAGE_CGROUP_FLAG_CACHE | PAGE_CGROUP_FLAG_ACTIVE;
 
 	lock_page_cgroup(page);
 	if (unlikely(page_get_page_cgroup(page))) {
@@ -739,8 +742,12 @@ int mem_cgroup_prepare_migration(struct page *page, struct page *newpage)
 	if (pc) {
 		mem = pc->mem_cgroup;
 		css_get(&mem->css);
-		if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
-			ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
+		if (pc->flags & PAGE_CGROUP_FLAG_CACHE) {
+			if (page_is_file_cache(page))
+				ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
+			else
+				ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
+		}
 	}
 	unlock_page_cgroup(page);
 	if (mem) {
--
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