Re: [RFC PATCH] mm: have kswapd only reclaiming use min protection on memcg

[Michal Hocko]

On Wed 27-10-21 15:46:19, Zhaoyang Huang wrote:
> On Wed, Oct 27, 2021 at 3:20 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
> >
> > On Wed 27-10-21 15:01:50, Huangzhaoyang wrote:
> > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > >
> > > For the kswapd only reclaiming, there is no chance to try again on
> > > this group while direct reclaim has. fix it by judging gfp flag.
> >
> > There is no problem description (same as in your last submissions. Have
> > you looked at the patch submission documentation as recommended
> > previously?).
> >
> > Also this patch doesn't make any sense. Both direct reclaim and kswapd
> > use a gfp mask which contains __GFP_DIRECT_RECLAIM (see balance_pgdat
> > for the kswapd part)..
> ok, but how does the reclaiming try with memcg's min protection on the
> alloc without __GFP_DIRECT_RECLAIM?

I do not follow. There is no need to protect memcg if the allocation
request doesn't have __GFP_DIRECT_RECLAIM because that would fail the
charge if a hard limit is reached, see try_charge_memcg and
gfpflags_allow_blocking check.

Background reclaim, on the other hand never breaches reclaim protection.

What is the actual problem you want to solve?

-- 
Michal Hocko
SUSE Labs