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from CAMSVWEXC02.scsc.local (2002:6a01:e348::6a01:e348) by CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Wed, 8 May 2024 15:28:51 +0100 Received: from CAMSVWEXC02.scsc.local ([::1]) by CAMSVWEXC02.scsc.local ([fe80::3c08:6c51:fa0a:6384%13]) with mapi id 15.00.1497.012; Wed, 8 May 2024 15:28:51 +0100 From: Daniel Gomez To: David Hildenbrand CC: Baolin Wang , "akpm@linux-foundation.org" , "hughd@google.com" , "willy@infradead.org" , "ioworker0@gmail.com" , "wangkefeng.wang@huawei.com" , "ying.huang@intel.com" , "21cnbao@gmail.com" <21cnbao@gmail.com>, "ryan.roberts@arm.com" , "shy828301@gmail.com" , "ziy@nvidia.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 0/8] add mTHP support for anonymous shmem Thread-Topic: [PATCH 0/8] add mTHP support for anonymous shmem Thread-Index: AQHaoTxlCSlVdbHh/EKIyyNA4DF787GNKsyAgAAqDYA= Date: Wed, 8 May 2024 14:28:50 +0000 Message-ID: In-Reply-To: Accept-Language: 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 wdIjzdaQ 5S34ilS0QH7JEj+UF0R5O6Uz/lbWOKt89zre2DGA2O9Ds+WZ3s6aDccDAQDe3OAW5XMHNNDSF3zoQ5QajMy6qmrPXGS3Cep+e71vLhYF9LslRNzElBpvnVohP0AcqqiUNZU1gaS23dYWXqIaSZQwGzuWneRZrnXj0aWgV 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: List-Subscribe: List-Unsubscribe: On Wed, May 08, 2024 at 01:58:19PM +0200, David Hildenbrand wrote: > On 08.05.24 13:39, Daniel Gomez wrote: > > On Mon, May 06, 2024 at 04:46:24PM +0800, Baolin Wang wrote: > > > Anonymous pages have already been supported for multi-size (mTHP) all= ocation > > > through commit 19eaf44954df, that can allow THP to be configured thro= ugh the > > > sysfs interface located at '/sys/kernel/mm/transparent_hugepage/hugep= age-XXkb/enabled'. > > >=20 > > > However, the anonymous shared pages will ignore the anonymous mTHP ru= le > > > configured through the sysfs interface, and can only use the PMD-mapp= ed > > > THP, that is not reasonable. Many implement anonymous page sharing th= rough > > > mmap(MAP_SHARED | MAP_ANONYMOUS), especially in database usage scenar= ios, > > > therefore, users expect to apply an unified mTHP strategy for anonymo= us pages, > > > also including the anonymous shared pages, in order to enjoy the bene= fits of > > > mTHP. For example, lower latency than PMD-mapped THP, smaller memory = bloat > > > than PMD-mapped THP, contiguous PTEs on ARM architecture to reduce TL= B miss etc. > > >=20 > > > The primary strategy is similar to supporting anonymous mTHP. Introdu= ce > > > a new interface '/mm/transparent_hugepage/hugepage-XXkb/shmem_enabled= ', > > > which can have all the same values as the top-level > > > '/sys/kernel/mm/transparent_hugepage/shmem_enabled', with adding a ne= w > > > additional "inherit" option. By default all sizes will be set to "nev= er" > > > except PMD size, which is set to "inherit". This ensures backward com= patibility > > > with the shmem enabled of the top level, meanwhile also allows indepe= ndent > > > control of shmem enabled for each mTHP. > >=20 > > I'm trying to understand the adoption of mTHP and how it fits into the = adoption > > of (large) folios that the kernel is moving towards. Can you, or anyone= involved > > here, explain this? How much do they overlap, and can we benefit from h= aving > > both? Is there any argument against the adoption of large folios here t= hat I > > might have missed? >=20 > mTHP are implemented using large folios, just like traditional PMD-sized = THP > are. (you really should explore the history of mTHP and how it all works > internally) I'll check more in deep the code. By any chance are any of you going to be = at LSFMM this year? I have this session [1] scheduled for Wednesday and it wou= ld be nice to get your feedback on it and if you see this working together wit= h mTHP/THP. [1] https://lore.kernel.org/all/4ktpayu66noklllpdpspa3vm5gbmb5boxskcj2q6qn7= md3pwwt@kvlu64pqwjzl/ >=20 > The biggest challenge with memory that cannot be evicted on memory pressu= re > to be reclaimed (in contrast to your ordinary files in the pagecache) is > memory waste, well, and placement of large chunks of memory in general, > during page faults. >=20 > In the worst case (no swap), you allocate a large chunk of memory once an= d > it will stick around until freed: no reclaim of that memory. I can see that path being triggered by some fstests but only for THP (where= we can actually reclaim memory). >=20 > That's the reason why THP for anonymous memory and SHMEM have toggles to > manually enable and configure them, in contrast to the pagecache. The sam= e > was done for mTHP for anonymous memory, and now (anon) shmem follows. >=20 > There are plans to have, at some point, have it all working automatically= , > but a lot for that for anonymous memory (and shmem similarly) is still > missing and unclear. Thanks. >=20 > --=20 > Cheers, >=20 > David / dhildenb > =