linux-kernel - Re: [PATCH v2 2/3] selftests/mm/charge_reserved_hugetlb.sh: add waits with timeout helper

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Message-ID: <CAEemH2cbnTwPFBYqnMB4nysUQ06FtCPBrVj1GYYGCyhseXPDpQ@mail.gmail.com>
Date: Sun, 21 Dec 2025 18:08:21 +0800
From: Li Wang <liwang@...hat.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: akpm@...ux-foundation.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Mark Brown <broonie@...nel.org>, Shuah Khan <shuah@...nel.org>, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v2 2/3] selftests/mm/charge_reserved_hugetlb.sh: add waits
 with timeout helper

On Sun, Dec 21, 2025 at 5:52 PM David Hildenbrand (Red Hat)
<david@...nel.org> wrote:
>
> On 12/21/25 10:35, Li Wang wrote:
> > David Hildenbrand (Red Hat) <david@...nel.org> wrote:
> >
> >> On 12/21/25 09:58, Li Wang wrote:
> >>> The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
> >>> unbounded and could hang forever if the expected cgroup file value never
> >>> appears (e.g. due to bugs, timing issues, or unexpected behavior).
> >>
> >> Did you actually hit that in practice? Just wondering.
> >
> > Yes.
> >
> > On an aarch64 64k setup with 512MB hugepages, the test failed earlier
> > (hugetlbfs got mounted with an effective size of 0 due to size=256M), so
> > write_to_hugetlbfs couldn’t allocate the expected pages. After that, the
> > script’s wait loops never observed the target value, so they spun forever.
>
> Okay, so essentially what you fix in patch #3, correct?
>
> It might make sense to reorder #2 and #3, and likely current #3 should
> get a Fixes: tag.

+1

> Then you can just briefly describe here that this was previously hit due
> to other tests issues. Although I wonder how much value this patch here
> as after #3 is in. But it looks like a cleanup and the timeout of 60s
> sounds reasonable.

The reason is that I improved the infinite loop before debugging the #3 issue.
But your suggestion makes sense, and I will reorder patch #2 and #3.

-- 
Regards,
Li Wang