linux-kernel - Re: [PATCH 0/7] vm, vmscan: enahance vmscan tracepoints

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Date:   Fri, 30 Dec 2016 09:11:17 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] vm, vmscan: enahance vmscan tracepoints

On Wed, Dec 28, 2016 at 04:30:25PM +0100, Michal Hocko wrote:
> Hi,
> while debugging [1] I've realized that there is some room for
> improvements in the tracepoints set we offer currently. I had hard times
> to make any conclusion from the existing ones. The resulting problem
> turned out to be active list aging [2] and we are missing at least two
> tracepoints to debug such a problem.
> 
> Some existing tracepoints could export more information to see _why_ the
> reclaim progress cannot be made not only _how much_ we could reclaim.
> The later could be seen quite reasonably from the vmstat counters
> already. It can be argued that we are showing too many implementation
> details in those tracepoints but I consider them way too lowlevel
> already to be usable by any kernel independent userspace. I would be
> _really_ surprised if anything but debugging tools have used them.
> 
> Any feedback is highly appreciated.
> 

There is some minor overhead introduced in some paths regardless of
whether the tracepoints are active or not but I suspect it's negligible
in the context of the overhead of reclaim in general so;

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs