All of lore.kernel.org
 help / color / mirror / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
	hannes@cmpxchg.org, mgorman@suse.de,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: warn about allocations which stall for too long
Date: Fri, 23 Sep 2016 17:02:34 +0200	[thread overview]
Message-ID: <20160923150234.GV4478@dhcp22.suse.cz> (raw)
In-Reply-To: <201609232336.FIH57364.FOVHtMFQLFSJOO@I-love.SAKURA.ne.jp>

On Fri 23-09-16 23:36:22, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > @@ -3659,6 +3661,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >  	else
> >  		no_progress_loops++;
> >  
> > +	/* Make sure we know about allocations which stall for too long */
> > +	if (!(gfp_mask & __GFP_NOWARN) && time_after(jiffies, alloc_start + stall_timeout)) {
> 
> Should we check !__GFP_NOWARN ? I think __GFP_NOWARN is likely used with
> __GFP_NORETRY, and __GFP_NORETRY is already checked by now.
> 
> I think printing warning regardless of __GFP_NOWARN is better because
> this check is similar to hungtask warning.

Well, if the user said to not warn we should really obey that. Why would
that matter?
 
> > +		pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
> > +				current->comm, jiffies_to_msecs(jiffies-alloc_start),
> > +				order, gfp_mask, &gfp_mask);
> > +		stall_timeout += 10 * HZ;
> > +		dump_stack();
> 
> Can we move this pr_warn() + dump_stack() to a separate function like
> 
> static void __warn_memalloc_stall(unsigned int order, gfp_t gfp_mask, unsigned long alloc_start)
> {
> 	pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
> 		current->comm, jiffies_to_msecs(jiffies-alloc_start),
> 		order, gfp_mask, &gfp_mask);
> 	dump_stack();
> }
> 
> in order to allow SystemTap scripts to perform additional actions by name (e.g.
> 
> # stap -g -e 'probe kernel.function("__warn_memalloc_stall").return { panic(); }

I find this reasoning and the use case really _absurd_, seriously! Pulling
the warning into a separate function might be reasonable regardless,
though. It matches warn_alloc_failed. Also if we find out we need some
rate limitting or more checks it might just turn out being easier to
follow rather than in the middle of an already complicated allocation
slow path. I just do not like that the stall_timeout would have to stay
in the original place or have it an in/out parameter.

> ) rather than by line number, and surround __warn_memalloc_stall() call with
> mutex in order to serialize warning messages because it is possible that
> multiple allocation requests are stalling?

we do not use any lock in warn_alloc_failed so why this should be any
different?

-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID
From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
	hannes@cmpxchg.org, mgorman@suse.de,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: warn about allocations which stall for too long
Date: Fri, 23 Sep 2016 17:02:34 +0200	[thread overview]
Message-ID: <20160923150234.GV4478@dhcp22.suse.cz> (raw)
In-Reply-To: <201609232336.FIH57364.FOVHtMFQLFSJOO@I-love.SAKURA.ne.jp>

On Fri 23-09-16 23:36:22, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > @@ -3659,6 +3661,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >  	else
> >  		no_progress_loops++;
> >  
> > +	/* Make sure we know about allocations which stall for too long */
> > +	if (!(gfp_mask & __GFP_NOWARN) && time_after(jiffies, alloc_start + stall_timeout)) {
> 
> Should we check !__GFP_NOWARN ? I think __GFP_NOWARN is likely used with
> __GFP_NORETRY, and __GFP_NORETRY is already checked by now.
> 
> I think printing warning regardless of __GFP_NOWARN is better because
> this check is similar to hungtask warning.

Well, if the user said to not warn we should really obey that. Why would
that matter?
 
> > +		pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
> > +				current->comm, jiffies_to_msecs(jiffies-alloc_start),
> > +				order, gfp_mask, &gfp_mask);
> > +		stall_timeout += 10 * HZ;
> > +		dump_stack();
> 
> Can we move this pr_warn() + dump_stack() to a separate function like
> 
> static void __warn_memalloc_stall(unsigned int order, gfp_t gfp_mask, unsigned long alloc_start)
> {
> 	pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
> 		current->comm, jiffies_to_msecs(jiffies-alloc_start),
> 		order, gfp_mask, &gfp_mask);
> 	dump_stack();
> }
> 
> in order to allow SystemTap scripts to perform additional actions by name (e.g.
> 
> # stap -g -e 'probe kernel.function("__warn_memalloc_stall").return { panic(); }

I find this reasoning and the use case really _absurd_, seriously! Pulling
the warning into a separate function might be reasonable regardless,
though. It matches warn_alloc_failed. Also if we find out we need some
rate limitting or more checks it might just turn out being easier to
follow rather than in the middle of an already complicated allocation
slow path. I just do not like that the stall_timeout would have to stay
in the original place or have it an in/out parameter.

> ) rather than by line number, and surround __warn_memalloc_stall() call with
> mutex in order to serialize warning messages because it is possible that
> multiple allocation requests are stalling?

we do not use any lock in warn_alloc_failed so why this should be any
different?

-- 
Michal Hocko
SUSE Labs

--
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>

  reply	other threads:[~2016-09-23 15:02 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-23  8:15 Michal Hocko
2016-09-23  8:15 ` Michal Hocko
2016-09-23  8:29 ` Hillf Danton
2016-09-23  8:29   ` Hillf Danton
2016-09-23  8:32   ` Michal Hocko
2016-09-23  8:32     ` Michal Hocko
2016-09-23  8:44     ` Hillf Danton
2016-09-23  8:44       ` Hillf Danton
2016-09-23  9:15       ` Michal Hocko
2016-09-23  9:15         ` Michal Hocko
2016-09-23 14:36 ` Tetsuo Handa
2016-09-23 14:36   ` Tetsuo Handa
2016-09-23 15:02   ` Michal Hocko [this message]
2016-09-23 15:02     ` Michal Hocko
2016-09-24  3:00     ` Tetsuo Handa
2016-09-24  3:00       ` Tetsuo Handa
2016-09-26  8:17       ` Michal Hocko
2016-09-26  8:17         ` Michal Hocko
2016-09-27 12:57         ` Tetsuo Handa
2016-09-27 12:57           ` Tetsuo Handa
2016-09-29  8:48           ` Michal Hocko
2016-09-29  8:48             ` Michal Hocko
2016-09-23 17:34 ` Dave Hansen
2016-09-23 17:34   ` Dave Hansen
2016-09-24 13:19   ` Balbir Singh
2016-09-24 13:19     ` Balbir Singh
2016-09-26  8:13     ` Michal Hocko
2016-09-26  8:13       ` Michal Hocko
2016-09-26  8:12   ` Michal Hocko
2016-09-26  8:12     ` Michal Hocko
2016-09-29  8:44 ` [PATCH 0/2] " Michal Hocko
2016-09-29  8:44   ` Michal Hocko
2016-09-29  8:44   ` [PATCH 1/2] mm: consolidate warn_alloc_failed users Michal Hocko
2016-09-29  8:44     ` Michal Hocko
2016-09-29  9:23     ` Vlastimil Babka
2016-09-29  9:23       ` Vlastimil Babka
2016-09-29  8:44   ` [PATCH 2/2] mm: warn about allocations which stall for too long Michal Hocko
2016-09-29  8:44     ` Michal Hocko
2016-09-29  9:02     ` Tetsuo Handa
2016-09-29  9:02       ` Tetsuo Handa
2016-09-29  9:10       ` Michal Hocko
2016-09-29  9:10         ` 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=20160923150234.GV4478@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=hannes@cmpxchg.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@suse.de \
    --cc=penguin-kernel@I-love.SAKURA.ne.jp \
    --subject='Re: [PATCH] mm: warn about allocations which stall for too long' \
    /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

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.