Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753499AbbKXMro (ORCPT ); Tue, 24 Nov 2015 07:47:44 -0500 Received: from relay.parallels.com ([195.214.232.42]:33946 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752868AbbKXMrn (ORCPT ); Tue, 24 Nov 2015 07:47:43 -0500 From: Vladimir Davydov To: Andrew Morton CC: Johannes Weiner , Michal Hocko , Vlastimil Babka , Mel Gorman , Dave Chinner , , Subject: [PATCH] vmscan: fix slab vs lru balance Date: Tue, 24 Nov 2015 15:47:21 +0300 Message-ID: <1448369241-26593-1-git-send-email-vdavydov@virtuozzo.com> X-Mailer: git-send-email 2.1.4 MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: US-EXCH2.sw.swsoft.com (10.255.249.46) To MSK-EXCH1.sw.swsoft.com (10.67.48.55) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1868 Lines: 51 The comment to shrink_slab states that the portion of kmem objects scanned by it equals the portion of lru pages scanned by shrink_zone over shrinker->seeks. shrinker->seeks is supposed to be equal to the number of disk seeks required to recreated an object. It is usually set to DEFAULT_SEEKS (2), which is quite logical, because most kmem objects (e.g. dentry or inode) require random IO to reread (seek to read and seek back). That said, one would expect that dcache is scanned two times less intensively than page cache, which sounds sane as dentries are generally more costly to recreate. However, the formula for distributing memory pressure between slab and lru actually looks as follows (see do_shrink_slab): lru_scanned objs_to_scan = objs_total * --------------- * 4 / shrinker->seeks lru_reclaimable That is dcache, as well as most of other slab caches, is scanned two times more aggressively than page cache. Fix this by dropping '4' from the equation above. Signed-off-by: Vladimir Davydov --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 97ba9e1cde09..9d553b07bb86 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -290,7 +290,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0); total_scan = nr; - delta = (4 * nr_scanned) / shrinker->seeks; + delta = nr_scanned / shrinker->seeks; delta *= freeable; do_div(delta, nr_eligible + 1); total_scan += delta; -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/