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

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Message-ID: <de5fa614-65c2-43d4-8c3c-549eeeaa5683@kernel.org>
Date: Sun, 21 Dec 2025 10:52:08 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Li Wang <liwang@...hat.com>
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 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.

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.

I know the reservation of hugetlb folios can take a rather long time in 
some environments, though.

-- 
Cheers

David