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Message-ID: <20231002144250.GA4414@cmpxchg.org>
Date: Mon, 2 Oct 2023 10:42:50 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Michal Hocko <mhocko@...e.com>, Nhat Pham <nphamcs@...il.com>,
akpm@...ux-foundation.org, riel@...riel.com,
roman.gushchin@...ux.dev, shakeelb@...gle.com,
muchun.song@...ux.dev, tj@...nel.org, lizefan.x@...edance.com,
shuah@...nel.org, yosryahmed@...gle.com, linux-mm@...ck.org,
kernel-team@...a.com, linux-kernel@...r.kernel.org,
cgroups@...r.kernel.org
Subject: Re: [PATCH 0/2] hugetlb memcg accounting
On Sun, Oct 01, 2023 at 04:27:30PM -0700, Mike Kravetz wrote:
> On 09/27/23 14:47, Johannes Weiner wrote:
> > On Wed, Sep 27, 2023 at 01:21:20PM +0200, Michal Hocko wrote:
> > > On Tue 26-09-23 12:49:47, Nhat Pham wrote:
> >
> > So that if you use 80% hugetlb, the other memory is forced to stay in
> > the remaining 20%, or it OOMs; and that if you don't use hugetlb, the
> > group is still allowed to use the full 100% of its host memory
> > allowance, without requiring some outside agent continuously
> > monitoring and adjusting the container limits.
>
> Jumping in late here as I was traveling last week. In addition, I want
> to state my limited cgroup knowledge up front.
>
> I was thinking of your scenario above a little differently. Suppose a
> group is up and running at almost 100% memory usage. However, the majority
> of that memory is reclaimable. Now, someone wants to allocate a 2M hugetlb
> page. There is not 2MB free, but we could easily reclaim 2MB to make room
> for the hugetlb page. I may be missing something, but I do not see how that
> is going to happen. It seems like we would really want that behavior.
But that is actually what it does, no?
alloc_hugetlb_folio
mem_cgroup_hugetlb_charge_folio
charge_memcg
try_charge
!page_counter_try_charge ?
!try_to_free_mem_cgroup_pages ?
mem_cgroup_oom
So it does reclaim when the hugetlb hits the cgroup limit. And if that
fails to make room, it OOMs the cgroup.
Or maybe I'm missing something?
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