linux-kernel - Re: [RFC] scripts: Include postprocessing script for memory allocation tracing

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Date:   Fri, 23 Sep 2016 10:07:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Janani Ravichandran <janani.rvchndrn@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, riel@...riel.com,
        akpm@...ux-foundation.org, vdavydov@...tuozzo.com, vbabka@...e.cz,
        mgorman@...hsingularity.net, rostedt@...dmis.org
Subject: Re: [RFC] scripts: Include postprocessing script for memory
 allocation tracing

On Thu 22-09-16 11:30:36, Janani Ravichandran wrote:
> 
> > On Sep 19, 2016, at 5:42 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > On Tue 13-09-16 14:04:49, Janani Ravichandran wrote:
> >> 
> >>> On Sep 12, 2016, at 8:16 AM, Michal Hocko <mhocko@...nel.org> wrote:
> >> 
> >> I’m using the function graph tracer to see how long __alloc_pages_nodemask()
> >> took.
> > 
> > How can you map the function graph tracer to a specif context? Let's say
> > I would like to know why a particular allocation took so long. Would
> > that be possible?
> 
> Maybe not. If the latencies are due to direct reclaim or memory compaction, you
> get some information from the tracepoints (like mm_vmscan_direct_reclaim_begin,
> mm_compaction_begin, etc). But otherwise, you don’t get any context information. 
> Function graph only gives the time spent in alloc_pages_nodemask() in that case.

Then I really think that we need a starting trace point. I think that
having the full context information is really helpful in order to
understand latencies induced by allocations.
-- 
Michal Hocko
SUSE Labs