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

From: Mel Gorman
Date: Fri Dec 30 2016 - 04:11:27 EST

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@xxxxxxx>

Mel Gorman