Messages in this thread Patch in this message | | | Date | Thu, 12 Nov 2020 20:28:44 +0800 | From | Feng Tang <> | Subject | Re: [LKP] Re: [mm/memcg] bd0b230fe1: will-it-scale.per_process_ops -22.7% regression |
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Hi Michal,
On Wed, Nov 04, 2020 at 09:15:46AM +0100, Michal Hocko wrote: > > > > Hi Michal, > > > > > > > > We used the default configure of cgroups, not sure what configuration you > > > > want, > > > > could you give me more details? and here is the cgroup info of will-it-scale > > > > process: > > > > > > > > $ cat /proc/3042/cgroup > > > > 12:hugetlb:/ > > > > 11:memory:/system.slice/lkp-bootstrap.service > > > > > > OK, this means that memory controler is enabled and in use. Btw. do you > > > get the original performance if you add one phony page_counter after the > > > union? > > > > > I add one phony page_counter after the union and re-test, the regression > > reduced to -1.2%. It looks like the regression caused by the data structure > > layout change. > > Thanks for double checking. Could you try to cache align the > page_counter struct? If that helps then we should figure which counters > acks against each other by adding the alignement between the respective > counters.
We tried below patch to make the 'page_counter' aligned.
diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index bab7e57..9efa6f7 100644 --- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h @@ -26,7 +26,7 @@ struct page_counter { /* legacy */ unsigned long watermark; unsigned long failcnt; -}; +} ____cacheline_internodealigned_in_smp; and with it, the -22.7% peformance change turns to a small -1.7%, which confirms the performance bump is caused by the change to data alignment.
After the patch, size of 'page_counter' increases from 104 bytes to 128 bytes, and the size of 'mem_cgroup' increases from 2880 bytes to 3008 bytes(with our kernel config). Another major data structure which contains 'page_counter' is 'hugetlb_cgroup', whose size will change from 912B to 1024B. Should we make these page_counters aligned to reduce cacheline conflict?
Thanks, Feng
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