Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 27 Aug 2020 10:00:28 -0400
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>,
        Chris Down <chris@chrisdown.name>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3] mm: memcg: Fix memcg reclaim soft lockup
Message-ID: <20200827140028.GA1002856@cmpxchg.org>
References: <1598495549-67324-1-git-send-email-xlpang@linux.alibaba.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1598495549-67324-1-git-send-email-xlpang@linux.alibaba.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Aug 27, 2020 at 10:32:29AM +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 a cond_resched() at the upper shrink_node_memcgs() to solve this
> issue, this will mean that we will get a scheduling point for each
> memcg in the reclaimed hierarchy without any dependency on the
> reclaimable memory in that memcg thus making it more predictable.
> 
> Acked-by: Chris Down <chris@chrisdown.name>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>