Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932304AbcCJUvm (ORCPT ); Thu, 10 Mar 2016 15:51:42 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:45706 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932162AbcCJUvj (ORCPT ); Thu, 10 Mar 2016 15:51:39 -0500 From: Johannes Weiner To: Andrew Morton Cc: Michal Hocko , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage Date: Thu, 10 Mar 2016 15:50:14 -0500 Message-Id: <1457643015-8828-2-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 2.7.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3758 Lines: 111 Setting the original memory.limit_in_bytes hardlimit is subject to a race condition when the desired value is below the current usage. The code tries a few times to first reclaim and then see if the usage has dropped to where we would like it to be, but there is no locking, and the workload is free to continue making new charges up to the old limit. Thus, attempting to shrink a workload relies on pure luck and hope that the workload happens to cooperate. To fix this in the cgroup2 memory.max knob, do it the other way round: set the limit first, then try enforcement. And if reclaim is not able to succeed, trigger OOM kills in the group. Keep going until the new limit is met, we run out of OOM victims and there's only unreclaimable memory left, or the task writing to memory.max is killed. This allows users to shrink groups reliably, and the behavior is consistent with what happens when new charges are attempted in excess of memory.max. Signed-off-by: Johannes Weiner --- Documentation/cgroup-v2.txt | 6 ++++++ mm/memcontrol.c | 38 ++++++++++++++++++++++++++++++++++---- 2 files changed, 40 insertions(+), 4 deletions(-) diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt index c709d7ebc092..2fd4cdb78445 100644 --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt @@ -1540,6 +1540,12 @@ system than killing the group. Otherwise, memory.max is there to limit this type of spillover and ultimately contain buggy or even malicious applications. +Setting the original memory.limit_in_bytes below the current usage was +subject to a race condition, where concurrent charges could cause the +limit setting to fail. memory.max on the other hand will first set the +limit to prevent new charges, and then reclaim and OOM kill until the +new limit is met - or the task writing to memory.max is killed. + The combined memory+swap accounting and limiting is replaced by real control over swap space. diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f7c9b4cbdf01..8614e0d750e5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1236,7 +1236,7 @@ static unsigned long mem_cgroup_get_limit(struct mem_cgroup *memcg) return limit; } -static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, +static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, int order) { struct oom_control oc = { @@ -1314,6 +1314,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, } unlock: mutex_unlock(&oom_lock); + return chosen; } #if MAX_NUMNODES > 1 @@ -5029,6 +5030,8 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); + unsigned int nr_reclaims = MEM_CGROUP_RECLAIM_RETRIES; + bool drained = false; unsigned long max; int err; @@ -5037,9 +5040,36 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, if (err) return err; - err = mem_cgroup_resize_limit(memcg, max); - if (err) - return err; + xchg(&memcg->memory.limit, max); + + for (;;) { + unsigned long nr_pages = page_counter_read(&memcg->memory); + + if (nr_pages <= max) + break; + + if (signal_pending(current)) { + err = -EINTR; + break; + } + + if (!drained) { + drain_all_stock(memcg); + drained = true; + continue; + } + + if (nr_reclaims) { + if (!try_to_free_mem_cgroup_pages(memcg, nr_pages - max, + GFP_KERNEL, true)) + nr_reclaims--; + continue; + } + + mem_cgroup_events(memcg, MEMCG_OOM, 1); + if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0)) + break; + } memcg_wb_domain_size_changed(memcg); return nbytes; -- 2.7.2