linux-kernel - [PATCH v11 08/15] vmscan: take at least one pass with shrinkers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <2ddb3940d9a96ba6625809a17e23ccb4e65fe29d.1385377616.git.vdavydov@parallels.com>
Date:	Mon, 25 Nov 2013 16:07:41 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	<akpm@...ux-foundation.org>, <mhocko@...e.cz>
CC:	<glommer@...nvz.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>, <devel@...nvz.org>
Subject: [PATCH v11 08/15] vmscan: take at least one pass with shrinkers

From: Glauber Costa <glommer@...nvz.org>

In very low free kernel memory situations, it may be the case that we
have less objects to free than our initial batch size. If this is the
case, it is better to shrink those, and open space for the new workload
then to keep them and fail the new allocations.

In particular, we are concerned with the direct reclaim case for memcg.
Although this same technique can be applied to other situations just as well,
we will start conservative and apply it for that case, which is the one
that matters the most.

Signed-off-by: Glauber Costa <glommer@...nvz.org>
CC: Dave Chinner <dchinner@...hat.com>
CC: Carlos Maiolino <cmaiolino@...hat.com>
CC: "Theodore Ts'o" <tytso@....edu>
CC: Al Viro <viro@...iv.linux.org.uk>
---
 mm/vmscan.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 36fc133..bfedcdc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -311,20 +311,33 @@ shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
 				nr_pages_scanned, lru_pages,
 				max_pass, delta, total_scan);
 
-	while (total_scan >= batch_size) {
+	do {
 		unsigned long ret;
+		unsigned long nr_to_scan = min(batch_size, total_scan);
+		struct mem_cgroup *memcg = shrinkctl->target_mem_cgroup;
+
+		/*
+		 * Differentiate between "few objects" and "no objects"
+		 * as returned by the count step.
+		 */
+		if (!total_scan)
+			break;
+
+		if ((total_scan < batch_size) &&
+		   !(memcg && memcg_kmem_is_active(memcg)))
+			break;
 
-		shrinkctl->nr_to_scan = batch_size;
+		shrinkctl->nr_to_scan = nr_to_scan;
 		ret = shrinker->scan_objects(shrinker, shrinkctl);
 		if (ret == SHRINK_STOP)
 			break;
 		freed += ret;
 
-		count_vm_events(SLABS_SCANNED, batch_size);
-		total_scan -= batch_size;
+		count_vm_events(SLABS_SCANNED, nr_to_scan);
+		total_scan -= nr_to_scan;
 
 		cond_resched();
-	}
+	} while (total_scan >= batch_size);
 
 	/*
 	 * move the unused scan count back into the shrinker in a
-- 
1.7.10.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/