Re: [PATCH v2] mm: memory: move mem_cgroup_charge() into alloc_anon_folio()

[Kefeng Wang]

On 2024/1/19 23:46, Michal Hocko wrote:
> On Fri 19-01-24 20:59:22, Kefeng Wang wrote:
> > > > > GFP_TRANSHUGE_LIGHT is more interesting though because those do not dive
> > > > > into the direct reclaim at all. With the current code they will reclaim
> > > > > charges to free up the space for the allocated THP page and that defeats
> > > > > the light mode. I have a vague recollection of preparing a patch to
> > > >
> > > > We are interesting to GFP_TRANSHUGE_LIGHT and _GFP_NORETRY as mentioned
> > > > above.
> > >
> > > if mTHP can be smaller than COSTLY_ORDER then you are correct and
> > > NORETRY makes a difference. Please mention that in the changelog as
> > > well.
> >
> > For memory cgroup charge, _GFP_NORETRY checked to make us directly skip
> > mem_cgroup_oom(), it has no concern with folio order or COSTLY_ORDER when
> > check _GFP_NORETRY in try_charge_memcg(), so I think NORETRY should
> > always make difference for all large order folio.
>
> we do not OOM on COSTLY_ORDER (see mem_cgroup_oom). So NORETRY really
> makes a difference for small orders.

I see what you mean, but we may describe the different processes, if
GFP_TRANSHUGE | __GFP_NORETRY returned from vma_thp_gfp_mask(),
then we never involved with mem_cgroup_oom(), since mem_cgroup_oom()
will be skipped in try_charge_memcg(), that is what I want to say,
and in this case, no oom for order < COSTLY_ORDER or order > 
COSTLY_ORDER. But if GFP is GFP_TRANHUGE, then we may enter 
mem_cgroup_oom(), and maybe oom if order < COSTLY_ORDER.

So Yes, NORETRY really makes a difference for small orders.