On Fri 30-12-16 09:11:17, Mel Gorman wrote: > 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;
I will work on improving some of them. E.g. I've dropped the change to free_hot_cold_page_list because that is indeed a hot path but other than that there shouldn't be any even medium hot path which should see any overhead I can see. If you are aware of any, please let me know and I will think about how to improve it. > Acked-by: Mel Gorman <[email protected]> Thanks! -- Michal Hocko SUSE Labs
