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

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Message-ID: <20171109100920.f7ox4nc63dr44gva@dhcp22.suse.cz>
Date:   Thu, 9 Nov 2017 11:09:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     peter enderborg <peter.enderborg@...y.com>
Cc:     peter enderborg <peter.enderborg@...ymobile.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "yuwang.yuwang" <yuwang.yuwang@...baba-inc.com>
Subject: Re: [PATCH] mm: don't warn about allocations which stall for too long

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