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Shutemov" To: Hugh Dickins Cc: Andrew Morton , Shakeel Butt , "Kirill A. Shutemov" , Yang Shi , Miaohe Lin , Mike Kravetz , Michal Hocko , Rik van Riel , Christoph Hellwig , Matthew Wilcox , "Eric W. Biederman" , Alexey Gladkov , Chris Wilson , Matthew Auld , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 07/16] memfd: memfd_create(name, MFD_HUGEPAGE) for shmem huge pages Message-ID: <20210804140341.m3ptxesrxwivqjmk@box.shutemov.name> References: <2862852d-badd-7486-3a8e-c5ea9666d6fb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B201F3008A9B Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=shutemov-name.20150623.gappssmtp.com header.s=20150623 header.b=cwWoGqnB; dmarc=none; spf=none (imf08.hostedemail.com: domain of kirill@shutemov.name has no SPF policy when checking 209.85.167.49) smtp.mailfrom=kirill@shutemov.name X-Stat-Signature: ek7kgupyotzoyuqim6f1a7ynjsrmxi4h X-HE-Tag: 1628085818-601651 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jul 30, 2021 at 12:45:49AM -0700, Hugh Dickins wrote: > Commit 749df87bd7be ("mm/shmem: add hugetlbfs support to memfd_create()") > in 4.14 added the MFD_HUGETLB flag to memfd_create(), to use hugetlbfs > pages instead of tmpfs pages: now add the MFD_HUGEPAGE flag, to use tmpfs > Transparent Huge Pages when they can be allocated (flag named to follow > the precedent of madvise's MADV_HUGEPAGE for THPs). I don't like the interface. THP supposed to be transparent, not yet another hugetlbs. > /sys/kernel/mm/transparent_hugepage/shmem_enabled "always" or "force" > already made this possible: but that is much too blunt an instrument, > affecting all the very different kinds of files on the internal shmem > mount, and was intended just for ease of testing hugepage loads. I wounder if your tried "always" in production? What breaks? Maybe we can make it work with a heuristic? This would speed up adoption. If a tunable needed, I would rather go with fadvise(). It would operate on a couple of bits per struct file and they get translated into VM_HUGEPAGE and VM_NOHUGEPAGE on mmap(). Later if needed fadvise() implementation may be extended to track requested ranges. But initially it can be simple. -- Kirill A. Shutemov