linux-kernel - [PATCH 02/11] memcg: Reclaim when more than one page needed.

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Message-Id: <1340633728-12785-3-git-send-email-glommer@parallels.com>
Date:	Mon, 25 Jun 2012 18:15:19 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<cgroups@...r.kernel.org>
Cc:	<linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, <devel@...nvz.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Tejun Heo <tj@...nel.org>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Glauber Costa <glommer@...allels.com>
Subject: [PATCH 02/11] memcg: Reclaim when more than one page needed.

From: Suleiman Souhlal <ssouhlal@...eBSD.org>

mem_cgroup_do_charge() was written before slab accounting, and expects
three cases: being called for 1 page, being called for a stock of 32 pages,
or being called for a hugepage.  If we call for 2 or 3 pages (and several
slabs used in process creation are such, at least with the debug options I
had), it assumed it's being called for stock and just retried without reclaiming.

Fix that by passing down a minsize argument in addition to the csize.

And what to do about that (csize == PAGE_SIZE && ret) retry?  If it's
needed at all (and presumably is since it's there, perhaps to handle
races), then it should be extended to more than PAGE_SIZE, yet how far?
And should there be a retry count limit, of what?  For now retry up to
COSTLY_ORDER (as page_alloc.c does), stay safe with a cond_resched(),
and make sure not to do it if __GFP_NORETRY.

[v4: fixed nr pages calculation pointed out by Christoph Lameter ]

Signed-off-by: Suleiman Souhlal <suleiman@...gle.com>
Signed-off-by: Glauber Costa <glommer@...allels.com>
Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/memcontrol.c |   23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9304db2..8e601e8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2158,8 +2158,16 @@ enum {
 	CHARGE_OOM_DIE,		/* the current is killed because of OOM */
 };
 
+/*
+ * We need a number that is small enough to be likely to have been
+ * reclaimed even under pressure, but not too big to trigger unnecessary 
+ * retries
+ */
+#define NR_PAGES_TO_RETRY 2
+
 static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
-				unsigned int nr_pages, bool oom_check)
+				unsigned int nr_pages, unsigned int min_pages,
+				bool oom_check)
 {
 	unsigned long csize = nr_pages * PAGE_SIZE;
 	struct mem_cgroup *mem_over_limit;
@@ -2182,18 +2190,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	} else
 		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
 	/*
-	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
-	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
-	 *
 	 * Never reclaim on behalf of optional batching, retry with a
 	 * single page instead.
 	 */
-	if (nr_pages == CHARGE_BATCH)
+	if (nr_pages > min_pages)
 		return CHARGE_RETRY;
 
 	if (!(gfp_mask & __GFP_WAIT))
 		return CHARGE_WOULDBLOCK;
 
+	if (gfp_mask & __GFP_NORETRY)
+		return CHARGE_NOMEM;
+
 	ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
 	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		return CHARGE_RETRY;
@@ -2206,7 +2214,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 * unlikely to succeed so close to the limit, and we fall back
 	 * to regular pages anyway in case of failure.
 	 */
-	if (nr_pages == 1 && ret)
+	if (nr_pages <= NR_PAGES_TO_RETRY && ret)
 		return CHARGE_RETRY;
 
 	/*
@@ -2341,7 +2349,8 @@ again:
 			nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
 		}
 
-		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
+		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
+		    oom_check);
 		switch (ret) {
 		case CHARGE_OK:
 			break;
-- 
1.7.10.2

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