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From: Mel Gorman <mgorman@techsingularity.net>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	linux-mm@kvack.org
Subject: Re: [PATCH] mm: avoid blocking lock_page() in kcompactd
Date: Fri, 10 Jan 2020 09:22:56 +0000	[thread overview]
Message-ID: <20200110092256.GN3466@techsingularity.net> (raw)
In-Reply-To: <20200109225646.22983-1-xiyou.wangcong@gmail.com>

On Thu, Jan 09, 2020 at 02:56:46PM -0800, Cong Wang wrote:
> We observed kcompactd hung at __lock_page():
> 
>  INFO: task kcompactd0:57 blocked for more than 120 seconds.
>        Not tainted 4.19.56.x86_64 #1
>  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>  kcompactd0      D    0    57      2 0x80000000
>  Call Trace:
>   ? __schedule+0x236/0x860
>   schedule+0x28/0x80
>   io_schedule+0x12/0x40
>   __lock_page+0xf9/0x120
>   ? page_cache_tree_insert+0xb0/0xb0
>   ? update_pageblock_skip+0xb0/0xb0
>   migrate_pages+0x88c/0xb90
>   ? isolate_freepages_block+0x3b0/0x3b0
>   compact_zone+0x5f1/0x870
>   kcompactd_do_work+0x130/0x2c0
>   ? __switch_to_asm+0x35/0x70
>   ? __switch_to_asm+0x41/0x70
>   ? kcompactd_do_work+0x2c0/0x2c0
>   ? kcompactd+0x73/0x180
>   kcompactd+0x73/0x180
>   ? finish_wait+0x80/0x80
>   kthread+0x113/0x130
>   ? kthread_create_worker_on_cpu+0x50/0x50
>   ret_from_fork+0x35/0x40
> 
> which faddr2line maps to:
> 
>   migrate_pages+0x88c/0xb90:
>   lock_page at include/linux/pagemap.h:483
>   (inlined by) __unmap_and_move at mm/migrate.c:1024
>   (inlined by) unmap_and_move at mm/migrate.c:1189
>   (inlined by) migrate_pages at mm/migrate.c:1419
> 
> Sometimes kcompactd eventually got out of this situation, sometimes not.
> 
> I think for memory compaction, it is a best effort to migrate the pages,
> so it doesn't have to wait for I/O to complete. It is fine to call
> trylock_page() here, which is pretty much similar to
> buffer_migrate_lock_buffers().
> 
> Given MIGRATE_SYNC_LIGHT is used on compaction path, just relax the
> check for it.
> 

Is this a single page being locked for a long time or multiple pages
being locked without reaching a reschedule point?

If it's a single page being locked, it's important to identify what held
page lock for 2 minutes because that is potentially a missing
unlock_page. The kernel in question is old -- 4.19.56. Are there any
other modifications to that kernel?

-- 
Mel Gorman
SUSE Labs


  parent reply	other threads:[~2020-01-10  9:23 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-09 22:56 [PATCH] mm: avoid blocking lock_page() in kcompactd Cong Wang
2020-01-10  0:28 ` Yang Shi
2020-01-10  1:01   ` Cong Wang
2020-01-10  4:51     ` Cong Wang
2020-01-10  7:38 ` Michal Hocko
2020-01-20 22:48   ` Cong Wang
2020-01-21  9:00     ` Michal Hocko
2020-01-26 19:53       ` Cong Wang
2020-01-26 23:39         ` Matthew Wilcox
2020-01-27 15:00           ` Michal Hocko
2020-01-27 19:06             ` Matthew Wilcox
2020-01-28  1:25               ` Yang Shi
2020-01-28  6:03                 ` Matthew Wilcox
2020-01-28  8:17               ` Michal Hocko
2020-01-28  8:30                 ` Matthew Wilcox
2020-01-28  9:13                   ` Michal Hocko
2020-01-28 10:48                     ` Matthew Wilcox
2020-01-28 11:39                       ` Michal Hocko
2020-01-28 19:44                         ` Cong Wang
2020-01-30 22:52                           ` Cong Wang
2020-02-13  7:48                         ` Michal Hocko
2020-02-13 16:46                           ` Matthew Wilcox
2020-02-13 17:08                             ` Michal Hocko
2020-02-14  4:27                               ` Matthew Wilcox
2020-02-14  6:55                                 ` Michal Hocko
2020-01-27 14:49         ` Michal Hocko
2020-01-28  0:46           ` Cong Wang
2020-01-28  8:22             ` Michal Hocko
2020-01-10  9:22 ` Mel Gorman [this message]
2020-01-20 22:41   ` Cong Wang
2020-01-21 19:21     ` Yang Shi
2020-01-21  8:26   ` Hillf Danton
2020-01-21  9:06     ` Michal Hocko

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