linux-kernel - Re: [PATCH] Add slowpath enter/exit trace events

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Date:   Thu, 23 Nov 2017 22:00:04 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     peter.enderborg@...y.com, Michal Hocko <mhocko@...e.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Harry Wentland <Harry.Wentland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tony Cheng <Tony.Cheng@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>
Subject: Re: [PATCH] Add slowpath enter/exit trace events

On 2017/11/23 19:43, peter.enderborg@...y.com wrote:
> The warning of slow allocation has been removed, this is
> a other way to fetch that information. But you need
> to enable the trace. The exit function also returns
> information about the number of retries, how long
> it was stalled and failure reason if that happened.

However, the fast path (I mean, get_page_from_freelist() at
"/* First allocation attempt */" label) might be slow, for it is
allowed to call node_reclaim() which can take uncontrollable
duration. I think that you need to add hooks like
http://lkml.kernel.org/r/1510833448-19918-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp does. ;-)