linux-kernel - Re: [RFC PATCH 1/3] mm: enable MADV

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Date:   Wed, 26 Jan 2022 19:19:15 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...e.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/3] mm: enable MADV_DONTNEED for hugetlb mappings

On 1/26/22 18:58, Naoya Horiguchi wrote:
> On Thu, Jan 13, 2022 at 10:03:06AM -0800, Mike Kravetz wrote:
>> MADV_DONTNEED is currently disabled for hugetlb mappings.  This
>> certainly makes sense in shared file mappings as the pagecache maintains
>> a reference to the page and it will never be freed.  However, it could
>> be useful to unmap and free pages in private mappings.
>>
>> The only thing preventing MADV_DONTNEED (and MADV_FREE) from working on
>> hugetlb mappings is a check in can_madv_lru_vma().  To allow support for
>> hugetlb mappings create and use a new routine madvise_dontneed_valid_vma()
>> that will allow hugetlb mappings.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> I briefly tested the patch and it seems that when calling madvise(MADV_DONTNEED)
> with the range unaligned to hugepage size (like 4kB) triggered the following crash.
> Could you double check around the address range issue?

Thanks Naoya!  My bad for not considering this and doing more testing.
-- 
Mike Kravetz