From: Johannes Weiner <hannes@cmpxchg.org>
To: Xunlei Pang <xlpang@linux.alibaba.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup
Date: Wed, 26 Aug 2020 12:43:32 -0400 [thread overview]
Message-ID: <20200826164332.GB995045@cmpxchg.org> (raw)
In-Reply-To: <1598449622-108748-1-git-send-email-xlpang@linux.alibaba.com>
On Wed, Aug 26, 2020 at 09:47:02PM +0800, Xunlei Pang wrote:
> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
> the target memcg doesn't have any reclaimable memory.
>
> It can be easily reproduced as below:
> watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
> CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
> Call Trace:
> shrink_lruvec+0x49f/0x640
> shrink_node+0x2a6/0x6f0
> do_try_to_free_pages+0xe9/0x3e0
> try_to_free_mem_cgroup_pages+0xef/0x1f0
> try_charge+0x2c1/0x750
> mem_cgroup_charge+0xd7/0x240
> __add_to_page_cache_locked+0x2fd/0x370
> add_to_page_cache_lru+0x4a/0xc0
> pagecache_get_page+0x10b/0x2f0
> filemap_fault+0x661/0xad0
> ext4_filemap_fault+0x2c/0x40
> __do_fault+0x4d/0xf9
> handle_mm_fault+0x1080/0x1790
>
> It only happens on our 1-vcpu instances, because there's no chance
> for oom reaper to run to reclaim the to-be-killed process.
>
> Add cond_resched() at the upper shrink_node_memcgs() to solve this
> issue, and any other possible issue like meomry.min protection.
>
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
This generally makes sense to me but really should have a comment:
/*
* This loop can become CPU-bound when there are thousands
* of cgroups that aren't eligible for reclaim - either
* because they don't have any pages, or because their
* memory is explicitly protected. Avoid soft lockups.
*/
cond_resched();
The placement in the middle of the multi-part protection checks is a
bit odd too. It would be better to have it either at the top of the
loop, or at the end, by replacing the continues with goto next.
next prev parent reply other threads:[~2020-08-26 16:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-26 13:47 [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Xunlei Pang
2020-08-26 14:10 ` Chris Down
2020-08-26 18:17 ` Chris Down
2020-08-26 15:05 ` Michal Hocko
2020-08-26 16:43 ` Johannes Weiner [this message]
2020-08-26 17:29 ` Michal Hocko
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