From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@suse.com
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
xiyou.wangcong@gmail.com, dave.hansen@intel.com,
hannes@cmpxchg.org, mgorman@suse.de, vbabka@suse.cz
Subject: Re: [PATCH] mm,page_alloc: Serialize warn_alloc() if schedulable.
Date: Mon, 10 Jul 2017 22:54:37 +0900 [thread overview]
Message-ID: <201707102254.ADA57090.SOFFOOMJFHQtVL@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20170710132139.GJ19185@dhcp22.suse.cz>
Michal Hocko wrote:
> On Sat 08-07-17 13:59:54, Tetsuo Handa wrote:
> [...]
> > Quoting from http://lkml.kernel.org/r/20170705081956.GA14538@dhcp22.suse.cz :
> > Michal Hocko wrote:
> > > On Sat 01-07-17 20:43:56, Tetsuo Handa wrote:
> > > > You are rejecting serialization under OOM without giving a chance to test
> > > > side effects of serialization under OOM at linux-next.git. I call such attitude
> > > > "speculation" which you never accept.
> > >
> > > No I am rejecting abusing the lock for purpose it is not aimed for.
> >
> > Then, why adding a new lock (not oom_lock but warn_alloc_lock) is not acceptable?
> > Since warn_alloc_lock is aimed for avoiding messages by warn_alloc() getting
> > jumbled, there should be no reason you reject this lock.
> >
> > If you don't like locks, can you instead accept below one?
>
> No, seriously! Just think about what you are proposing. You are stalling
> and now you will stall _random_ tasks even more. Some of them for
> unbound amount of time because of inherent unfairness of cmpxchg.
The cause of stall when oom_lock is already held is that threads which failed to
hold oom_lock continue almost busy looping; schedule_timeout_uninterruptible(1) is
not sufficient when there are multiple threads doing the same thing, for direct
reclaim/compaction consumes a lot of CPU time.
What makes this situation worse is, since warn_alloc() periodically appends to
printk() buffer, the thread inside the OOM killer with oom_lock held can stall
forever due to cond_resched() from console_unlock() from printk().
Below change significantly reduces possibility of falling into printk() v.s. oom_lock
lockup problem, for the thread inside the OOM killer with oom_lock held no longer
blocks inside printk(). Though there still remains possibility of sleeping for
unexpectedly long at schedule_timeout_killable(1) with the oom_lock held.
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1051,8 +1051,10 @@ bool out_of_memory(struct oom_control *oc)
panic("Out of memory and no killable processes...\n");
}
if (oc->chosen && oc->chosen != (void *)-1UL) {
+ preempt_disable();
oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
"Memory cgroup out of memory");
+ preempt_enable_no_resched();
/*
* Give the killed process a good chance to exit before trying
* to allocate memory again.
I wish we could agree with applying this patch until printk-kthread can
work reliably...
>
> If there is a _real_ problem it should be debugged and fixed. If this
> is a limitation of what printk can handle then we should think how to
> throttle it even more (e.g. does it make much sense to dump_stack when
> it hasn't changed since the last time?). If this is about dump_stack
> taking too long then we should look into it but we definitely should add
> a more on top.
The real problem is lack of CPU time for reclaiming memory when allocating
threads failed to hold oom_lock. And you are refusing to allow allocating
threads give CPU time to the thread holding oom_lock.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-07-10 13:55 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-01 11:43 [PATCH] mm,page_alloc: Serialize warn_alloc() if schedulable Tetsuo Handa
2017-06-01 11:59 ` Michal Hocko
2017-06-01 13:11 ` Tetsuo Handa
2017-06-01 13:28 ` Michal Hocko
2017-06-01 22:10 ` Andrew Morton
2017-06-02 7:18 ` Michal Hocko
2017-06-02 11:13 ` Tetsuo Handa
2017-06-02 12:15 ` Michal Hocko
2017-06-02 17:13 ` Tetsuo Handa
2017-06-02 21:57 ` Cong Wang
2017-06-04 8:58 ` Tetsuo Handa
2017-06-04 15:05 ` Michal Hocko
2017-06-04 21:43 ` Tetsuo Handa
2017-06-05 5:37 ` Michal Hocko
2017-06-05 18:15 ` Cong Wang
2017-06-06 9:17 ` Michal Hocko
2017-06-05 18:25 ` Cong Wang
2017-06-22 10:35 ` Tetsuo Handa
2017-06-22 22:53 ` Cong Wang
2017-06-02 16:59 ` Cong Wang
2017-06-02 19:59 ` Andrew Morton
2017-06-03 2:57 ` Tetsuo Handa
2017-06-03 7:32 ` Michal Hocko
2017-06-03 8:36 ` Tetsuo Handa
2017-06-05 7:10 ` Sergey Senozhatsky
2017-06-05 9:36 ` Sergey Senozhatsky
2017-06-05 15:02 ` Tetsuo Handa
2017-06-03 13:21 ` Tetsuo Handa
2017-07-08 4:59 ` Tetsuo Handa
2017-07-10 13:21 ` Michal Hocko
2017-07-10 13:54 ` Tetsuo Handa [this message]
2017-07-10 14:14 ` Michal Hocko
2017-07-11 13:10 ` Tetsuo Handa
2017-07-11 13:49 ` Michal Hocko
2017-07-11 14:58 ` Petr Mladek
2017-07-11 22:06 ` Tetsuo Handa
2017-07-12 8:54 ` Michal Hocko
2017-07-12 12:23 ` Tetsuo Handa
2017-07-12 12:41 ` Michal Hocko
2017-07-14 12:30 ` Tetsuo Handa
2017-07-14 12:48 ` Michal Hocko
2017-08-09 6:14 ` Tetsuo Handa
2017-08-09 13:01 ` Tetsuo Handa
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=201707102254.ADA57090.SOFFOOMJFHQtVL@I-love.SAKURA.ne.jp \
--to=penguin-kernel@i-love.sakura.ne.jp \
--cc=akpm@linux-foundation.org \
--cc=dave.hansen@intel.com \
--cc=hannes@cmpxchg.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mhocko@suse.com \
--cc=vbabka@suse.cz \
--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).