From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>, Mel Gorman <mgorman@suse.de>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] mm: avoid blocking lock_page() in kcompactd
Date: Mon, 27 Jan 2020 16:00:24 +0100 [thread overview]
Message-ID: <20200127150024.GN1183@dhcp22.suse.cz> (raw)
In-Reply-To: <20200126233935.GA11536@bombadil.infradead.org>
On Sun 26-01-20 15:39:35, Matthew Wilcox wrote:
> On Sun, Jan 26, 2020 at 11:53:55AM -0800, Cong Wang wrote:
> > On Tue, Jan 21, 2020 at 1:00 AM Michal Hocko <mhocko@kernel.org> wrote:
> > >
> > > On Mon 20-01-20 14:48:05, Cong Wang wrote:
> > > > It got stuck somewhere along the call path of mem_cgroup_try_charge(),
> > > > and the trace events of mm_vmscan_lru_shrink_inactive() indicates this
> > > > too:
> > >
> > > So it seems that you are condending on the page lock. It is really
> > > unexpected that the reclaim would take that long though. Please try to
> > > enable more vmscan tracepoints to see where the time is spent.
> >
> > I suspect the process gets stuck in the retry loop in try_charge(), as
> > the _shortest_ stacktrace of the perf samples indicated:
> >
> > cycles:ppp:
> > ffffffffa72963db mem_cgroup_iter
> > ffffffffa72980ca mem_cgroup_oom_unlock
> > ffffffffa7298c15 try_charge
> > ffffffffa729a886 mem_cgroup_try_charge
> > ffffffffa720ec03 __add_to_page_cache_locked
> > ffffffffa720ee3a add_to_page_cache_lru
> > ffffffffa7312ddb iomap_readpages_actor
> > ffffffffa73133f7 iomap_apply
> > ffffffffa73135da iomap_readpages
> > ffffffffa722062e read_pages
> > ffffffffa7220b3f __do_page_cache_readahead
> > ffffffffa7210554 filemap_fault
> > ffffffffc039e41f __xfs_filemap_fault
> > ffffffffa724f5e7 __do_fault
> > ffffffffa724c5f2 __handle_mm_fault
> > ffffffffa724cbc6 handle_mm_fault
> > ffffffffa70a313e __do_page_fault
> > ffffffffa7a00dfe page_fault
> >
> > But I don't see how it could be, the only possible case is when
> > mem_cgroup_oom() returns OOM_SUCCESS. However I can't
> > find any clue in dmesg pointing to OOM. These processes in the
> > same memcg are either running or sleeping (that is not exiting or
> > coredump'ing), I don't see how and why they could be selected as
> > a victim of OOM killer. I don't see any signal pending either from
> > their /proc/X/status.
>
> I think this is a situation where we might end up with a genuine deadlock
> if we're not trylocking the pages. readahead allocates a batch of
> locked pages and adds them to the pagecache. If it has allocated,
> say, 5 pages, successfully inserted the first three into i_pages, then
> needs to allocate memory to insert the fourth one into i_pages, and
> the process then attempts to migrate the pages which are still locked,
> they will never come unlocked because they haven't yet been submitted
> to the filesystem for reading.
Just to make sure I understand. Do you mean this?
lock_page(A)
alloc_pages
try_to_compact_pages
compact_zone_order
compact_zone(MIGRATE_SYNC_LIGHT)
migrate_pages
unmap_and_move
__unmap_and_move
lock_page(A)
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-01-27 15:00 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200127150024.GN1183@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=vbabka@suse.cz \
--cc=willy@infradead.org \
--cc=xiyou.wangcong@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).