linux-kernel - Re: [PATCH] mm, hugepages: fix size in hugetlb mremap() test

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Message-ID: <6ebcffe2-9513-cbea-a206-15ba927416c7@oracle.com>
Date:   Tue, 23 Nov 2021 17:08:02 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mina Almasry <almasrymina@...gle.com>
Subject: Re: [PATCH] mm, hugepages: fix size in hugetlb mremap() test

On 11/23/21 12:46, Yosry Ahmed wrote:
> The hugetlb vma mremap() test mentions in the header comment that it
> uses 10MB worth of huge pages, when it actually uses 1GB. This causes
> the test to fail on devices with smaller memories.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
>  tools/testing/selftests/vm/hugepage-mremap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I'll let Mina comment, but I think I know what happened.

The original version of the test did indeed use 10MB.  However, the mremap
code must 'unshare' and shared pmd mappings before remapping.  Since sharing
requires mappings of at least 1GB, the size was changed to make sure unsharing
worked.

In the end, I believe I suggested adding hugepage-mremap to run_vmtests.sh.
The script does not try to configure a GB worth of huge pages.  And, I think
it is somewhat unreasonable to suggest users gave a spare GB to run the test.

I'm OK with restoring the original value.

Acked-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz