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

From: Michal Hocko <mhocko@suse.com>
To: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	ryan.roberts@arm.com, Matthew Wilcox <willy@infradead.org>,
	David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v2] mm: memory: move mem_cgroup_charge() into alloc_anon_folio()
Date: Fri, 19 Jan 2024 16:46:07 +0100	[thread overview]
Message-ID: <ZaqZPxDUOuxRWB5l@tiehlicka> (raw)
In-Reply-To: <14ae628d-a9ef-42f3-9201-e90c5c88c133@huawei.com>

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.
-- 
Michal Hocko
SUSE Labs