linux-kernel - Re: [PATCH 0/2] hugetlb memcg accounting

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Message-ID: <20231001232730.GA11194@monkey>
Date:   Sun, 1 Oct 2023 16:27:30 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Johannes Weiner <hannes@...xchg.org>
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 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.
-- 
Mike Kravetz