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

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Date:   Thu, 27 Oct 2016 11:42:35 -0400
From:   Janani Ravichandran <janani.rvchndrn@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Janani Ravichandran <janani.rvchndrn@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] scripts: Include postprocessing script for memory allocation tracing

> On Oct 21, 2016, at 3:08 AM, Michal Hocko <mhocko@...nel.org> wrote:
> 
> Interesting.
> $ cat /debug/tracing/available_tracers 
> function_graph preemptirqsoff preemptoff irqsoff function nop
> 
> Do I have to configure anything specially? And if I do why isn't it any
> better to simply add a start tracepoint and make this available also to
> older kernels?

Well, you just need to enable the function_graph tracer in the tracing directory:
echo function_graph > current_tracer,

set funcgraph-proc in trace_options to get process information:
echo funcgraph-proc > trace_options,

set funcgraph-abstime in trace_options to get timestamp,
echo funcgraph-abstime > trace_options

set all the functions we’d like to observe as filters. For e.g.
echo __alloc_pages_nodemask > set_ftrace_filter

and enable the tracepoints we would like to get information from.

I didn’t add a begin tracepoint for this as Steven Rostedt had suggested
using function graph instead of begin/end tracepoints (we already have
a tracepoint in __alloc_pages_nodemask - trace_mm_page_alloc to get 
some information about the allocation and we can just use function graph 
to see how long __alloc_pages_nodemask() takes).

Janani

> -- 
> Michal Hocko
> SUSE Labs