Re: [PATCH] mm: don't warn about allocations which stall for too long

From: Michal Hocko <mhocko@kernel.org>
To: peter enderborg <peter.enderborg@sony.com>
Cc: peter enderborg <peter.enderborg@sonymobile.com>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Mel Gorman <mgorman@suse.de>, Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>
Subject: Re: [PATCH] mm: don't warn about allocations which stall for too long
Date: Thu, 9 Nov 2017 11:09:20 +0100	[thread overview]
Message-ID: <20171109100920.f7ox4nc63dr44gva@dhcp22.suse.cz> (raw)
In-Reply-To: <ef81333e-0e19-c6f6-a960-093dc60fb75c@sony.com>

On Thu 09-11-17 10:34:46, peter enderborg wrote:
> On 11/09/2017 09:52 AM, Michal Hocko wrote:
> > I am not sure. I would rather see a tracepoint to mark the allocator
> > entry. This would allow both 1) measuring the allocation latency (to
> > compare it to the trace_mm_page_alloc and 2) check for stalls with
> > arbitrary user defined timeout (just print all allocations which haven't
> > passed trace_mm_page_alloc for the given amount of time).
> 
> Traces are not that expensive, but there are more than few in calls
> in this path. And Im trying to keep it as small that it can used for
> maintenance versions too.
>
> This is suggestion is a quick way of keeping the current solution for
> the ones that are interested the slow allocations. If we are going
> for a solution with a time-out parameter from the user what interface
> do you suggest to do this configuration. A filter parameter for the
> event?

I meant to do all that in postprocessing. So no specific API is needed,
just parse the output. Anyway, it seems that the printk will be put in
shape in a forseeable future so we might preserve the stall warning
after all. It is the show_mem part which is interesting during that
warning.

-- 
Michal Hocko
SUSE Labs

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