Re: [PATCH 3/3] mm/memcg: add next_mz back if not reclaimed yet

Michal Hocko
2022-03-10T08:54:03Z

On Thu 10-03-22 01:13:50, Wei Yang wrote:
> On Wed, Mar 09, 2022 at 02:48:45PM +0100, Michal Hocko wrote:
> >[Cc Tim - the patch is http://lkml.kernel.org/r/20220308012047.26638-3-richard.weiyang@gmail.com]
> >
> >On Wed 09-03-22 00:46:20, Wei Yang wrote:
> >> On Tue, Mar 08, 2022 at 09:17:58AM +0100, Michal Hocko wrote:
> >> >On Tue 08-03-22 01:20:47, Wei Yang wrote:
> >> >> next_mz is removed from rb_tree, let's add it back if no reclaim has
> >> >> been tried.
> >> >
> >> >Could you elaborate more why we need/want this?
> >> >
> >>
> >> Per my understanding, we add back the right most node even reclaim makes no
> >> progress, so it is reasonable to add back a node if we didn't get a chance to
> >> do reclaim on it.
> >
> >Your patch sounded familiar and I can remember now. The same fix has
> >been posted by Tim last year
> >https://lore.kernel.org/linux-mm/8d35206601ccf0e1fe021d24405b2a0c2f4e052f.1613584277.git.tim.c.chen@linux.intel.com/
> >It was posted with other changes to the soft limit code which I didn't
> >like but I have acked this particular one. Not sure what has happened
> >with it afterwards.
>
> Because of this ?
> 4f09feb8bf: vm-scalability.throughput -4.3% regression
> https://lore.kernel.org/linux-mm/20210302062521.GB23892@xsang-OptiPlex-9020/

That was a regression for a different patch in the series AFAICS:
: FYI, we noticed a -4.3% regression of vm-scalability.throughput due to commit:
:
: commit: 4f09feb8bf083be3834080ddf3782aee12a7c3f7 ("mm: Force update of mem cgroup soft limit tree on usage excess")

That patch has played with how often memcg_check_events is called and
that can lead to a visible performance difference.
--
Michal Hocko
SUSE Labs