On Thu 05-09-19 10:14:52, Joel Fernandes wrote: > On Thu, Sep 05, 2019 at 12:54:24PM +0200, Michal Hocko wrote: > > On Wed 04-09-19 12:28:08, Joel Fernandes wrote: > > > On Wed, Sep 4, 2019 at 11:38 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Wed 04-09-19 11:32:58, Joel Fernandes wrote: > > > > > On Wed, Sep 04, 2019 at 10:45:08AM +0200, Michal Hocko wrote: > > > > > > On Tue 03-09-19 16:09:05, Joel Fernandes (Google) wrote: > > > > > > > Useful to track how RSS is changing per TGID to detect spikes in RSS and > > > > > > > memory hogs. Several Android teams have been using this patch in various > > > > > > > kernel trees for half a year now. Many reported to me it is really > > > > > > > useful so I'm posting it upstream. > > > > > > > > > > > > > > Initial patch developed by Tim Murray. Changes I made from original patch: > > > > > > > o Prevent any additional space consumed by mm_struct. > > > > > > > o Keep overhead low by checking if tracing is enabled. > > > > > > > o Add some noise reduction and lower overhead by emitting only on > > > > > > > threshold changes. > > > > > > > > > > > > Does this have any pre-requisite? I do not see trace_rss_stat_enabled in > > > > > > the Linus tree (nor in linux-next). > > > > > > > > > > No, this is generated automatically by the tracepoint infrastructure when a > > > > > tracepoint is added. > > > > > > > > OK, I was not aware of that. > > > > > > > > > > Besides that why do we need batching in the first place. Does this have a > > > > > > measurable overhead? How does it differ from any other tracepoints that we > > > > > > have in other hotpaths (e.g. page allocator doesn't do any checks). > > > > > > > > > > We do need batching not only for overhead reduction, > > > > > > > > What is the overhead? > > > > > > The overhead is occasionally higher without the threshold (that is if we > > > trace every counter change). I would classify performance benefit to be > > > almost the same and within the noise. > > > > OK, so the additional code is not really justified. > > It is really justified. Did you read the whole of the last email? Of course I have. The information that numbers are in noise with some outliers (without any details about the underlying reason) is simply showing that you are optimizing something probably not worth it. I would recommend adding a simple tracepoint. That should be pretty non controversial. And if you want to add an optimization on top then provide data to justify it. -- Michal Hocko SUSE Labs
