linux-kernel - [patch 06/10] mm: memcg: remove optimization of keeping the root_mem

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Message-Id: <1320787408-22866-7-git-send-email-jweiner@redhat.com>
Date:	Tue,  8 Nov 2011 22:23:24 +0100
From:	Johannes Weiner <jweiner@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <bsingharora@...il.com>,
	Ying Han <yinghan@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [patch 06/10] mm: memcg: remove optimization of keeping the root_mem_cgroup LRU lists empty

root_mem_cgroup, lacking a configurable limit, was never subject to
limit reclaim, so the pages charged to it could be kept off its LRU
lists.  They would be found on the global per-zone LRU lists upon
physical memory pressure and it made sense to avoid uselessly linking
them to both lists.

The global per-zone LRU lists are about to go away on memcg-enabled
kernels, with all pages being exclusively linked to their respective
per-memcg LRU lists.  As a result, pages of the root_mem_cgroup must
also be linked to its LRU lists again.  This is purely about the LRU
list, root_mem_cgroup is still not charged.

The overhead is temporary until the double-LRU scheme is going away
completely.

Signed-off-by: Johannes Weiner <jweiner@...hat.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Reviewed-by: Kirill A. Shutemov <kirill@...temov.name>
---
 mm/memcontrol.c |   12 ++----------
 1 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4305686..bf84e2b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -965,8 +965,6 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
 	mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
 	/* huge page split is done under lru_lock. so, we have no races. */
 	MEM_CGROUP_ZSTAT(mz, lru) -= 1 << compound_order(page);
-	if (mem_cgroup_is_root(pc->mem_cgroup))
-		return;
 	VM_BUG_ON(list_empty(&pc->lru));
 	list_del_init(&pc->lru);
 }
@@ -991,13 +989,11 @@ void mem_cgroup_rotate_reclaimable_page(struct page *page)
 		return;
 
 	pc = lookup_page_cgroup(page);
-	/* unused or root page is not rotated. */
+	/* unused page is not rotated. */
 	if (!PageCgroupUsed(pc))
 		return;
 	/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
 	smp_rmb();
-	if (mem_cgroup_is_root(pc->mem_cgroup))
-		return;
 	mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
 	list_move_tail(&pc->lru, &mz->lists[lru]);
 }
@@ -1011,13 +1007,11 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
 		return;
 
 	pc = lookup_page_cgroup(page);
-	/* unused or root page is not rotated. */
+	/* unused page is not rotated. */
 	if (!PageCgroupUsed(pc))
 		return;
 	/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
 	smp_rmb();
-	if (mem_cgroup_is_root(pc->mem_cgroup))
-		return;
 	mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
 	list_move(&pc->lru, &mz->lists[lru]);
 }
@@ -1049,8 +1043,6 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
 	/* huge page split is done under lru_lock. so, we have no races. */
 	MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
 	SetPageCgroupAcctLRU(pc);
-	if (mem_cgroup_is_root(pc->mem_cgroup))
-		return;
 	list_add(&pc->lru, &mz->lists[lru]);
 }
 
-- 
1.7.6.4

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