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

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Date:   Wed, 28 Dec 2016 16:30:25 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     <linux-mm@...ck.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 0/7] vm, vmscan: enahance vmscan tracepoints

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.

[1] http://lkml.kernel.org/r/20161215225702.GA27944@boerne.fritz.box
[2] http://lkml.kernel.org/r/20161223105157.GB23109@dhcp22.suse.cz