Re: [PATCH] mm: memcontrol: skip propagate percpu vmstat values to current memcg

[Michal Hocko]

On Tue 19-01-21 11:58:42, Johannes Weiner wrote:
> On Tue, Jan 19, 2021 at 01:27:44PM +0800, Muchun Song wrote:
> > The current memcg will be freed soon, so updating it's vmstat and
> > vmevent values is pointless. Just skip updating it.
> > 
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> 
> Oof, that's pretty subtle! Somebody trying to refactor that code for
> other purposes may not immediately notice that optimization and add
> potentially tedious bugs.

Absolutely agreed!

> How much does this save? Cgroup creation and deletion isn't really
> considered a hot path. It takes global locks and such...

This is not the first time when an (micro)optimization is posted without
any data showing benefit or otherwise appealing justification. Sigh.

-- 
Michal Hocko
SUSE Labs