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s=arc-20220608; d=hostedemail.com; t=1713947213; a=rsa-sha256; cv=none; b=zGTqtG39G9DhobX6Iem9yBgSC63ge/dSN35DLEYaWFgZZqPK0NJf9+tlwGETqIKuNo3q2s zbKbHe2KLec8rgmZF4dvx1tXNu9eGiVzDQTjZrCq9daMckW5HUvqqKDmlZiJaGtfQaG6OY YMGitMJngxVkVpBJpn8h1DtnehtUSD0= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=none; spf=pass (imf26.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E9A8D339; Wed, 24 Apr 2024 01:27:19 -0700 (PDT) Received: from [10.57.74.127] (unknown [10.57.74.127]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 95F6C3F64C; Wed, 24 Apr 2024 01:26:50 -0700 (PDT) Message-ID: <80b5f87e-c156-4ccc-98f0-96f1fd864273@arm.com> Date: Wed, 24 Apr 2024 09:26:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/5] add mTHP support for anonymous share pages Content-Language: en-GB To: Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ying.huang@intel.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <4b998e7d-153f-48cc-a9bb-8c84bb675581@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 45F7E140025 X-Rspam-User: X-Stat-Signature: n1f3bxjdxpsxs874z145ogzieh4jjnnm X-HE-Tag: 1713947213-826405 X-HE-Meta: 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 F7ztXxvT UIQodKqm8zuh21GhiHarElqG2y+R1tbcYZf5aW2w8uUkycspBpKtzhRgn7Ra53IrMaVYgtdCZNJNWxkkvN+xr6kWMHdHVWM3+zdQlrhlmx9jIi6SO5hKkQipv+B6iX0r2VHGc+ADuhpdLtNkBncP9TpFHqnQkBKgIwFSIZYsGE50bWIzH0/n2uSqv3wQmsAEXdGko 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 24/04/2024 07:55, Baolin Wang wrote: > > > On 2024/4/23 18:41, Ryan Roberts wrote: >> On 22/04/2024 08:02, Baolin Wang wrote: >>> Anonymous pages have already been supported for multi-size (mTHP) allocation >>> through commit 19eaf44954df, that can allow THP to be configured through the >>> sysfs interface located at >>> '/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled'. >>> >>> However, the anonymous shared pages will ignore the anonymous mTHP rule >>> configured through the sysfs interface, and can only use the PMD-mapped >>> THP, that is not reasonable. Many implement anonymous page sharing through >>> mmap(MAP_SHARED | MAP_ANONYMOUS), especially in database usage scenarios, >>> therefore, users expect to apply an unified mTHP strategy for anonymous pages, >>> also including the anonymous shared pages, in order to enjoy the benefits of >>> mTHP. For example, lower latency than PMD-mapped THP, smaller memory bloat >>> than PMD-mapped THP, contiguous PTEs on ARM architecture to reduce TLB miss etc. >> >> This sounds like a very useful addition! >> >> Out of interest, can you point me at any workloads (and off-the-shelf benchmarks >> for those workloads) that predominantly use shared anon memory? > > As far as I know, some database related workloads make extensive use of shared > anonymous page, such as PolarDB[1] in our Alibaba fleet, or MySQL likely also > uses shared anonymous memory. And I still need to do some investigation to > measure the performance. > > [1] https://github.com/ApsaraDB/PolarDB-for-PostgreSQL Thanks for the pointer! > >>> The primary strategy is that, the use of huge pages for anonymous shared pages >>> still follows the global control determined by the mount option "huge=" >>> parameter >>> or the sysfs interface at '/sys/kernel/mm/transparent_hugepage/shmem_enabled'. >>> The utilization of mTHP is allowed only when the global 'huge' switch is >>> enabled. >>> Subsequently, the mTHP sysfs interface >>> (/sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled) >>> is checked to determine the mTHP size that can be used for large folio >>> allocation >>> for these anonymous shared pages. >> >> I'm not sure about this proposed control mechanism; won't it break >> compatibility? I could be wrong, but I don't think shmem's use of THP used to >> depend upon the value of /sys/kernel/mm/transparent_hugepage/enabled? So it > > Yes, I realized this after more testing. > >> doesn't make sense to me that we now depend upon the >> /sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled values (which by >> default disables all sizes except 2M, which is set to "inherit" from >> /sys/kernel/mm/transparent_hugepage/enabled). >> >> The other problem is that shmem_enabled has a different set of options >> (always/never/within_size/advise/deny/force) to enabled (always/madvise/never) >> >> Perhaps it would be cleaner to do the same trick we did for enabled; Introduce >> /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, >> plus the additional "inherit" option. By default all sizes will be set to >> "never" except 2M, which is set to "inherit". > > Sounds good to me. But I do not want to copy all same values from top-level > '/sys/kernel/mm/transparent_hugepage/shmem_enabled': > always within_size advise never deny force > > For mTHP's shmem_enabled interface, we can just keep below values: > always within_size advise never > > Cause when checking if mTHP can be used for anon shmem, 'deny' is equal to > 'never', and 'force' is equal to 'always'. I'll admit it wasn't completely clear to me after reading the docs, but my rough understanding is: - /sys/kernel/mm/transparent_hugepage/shmem_enabled controls mmap(SHARED|ANON) allocations (mostly; see rule 3) - huge=... controls tmpfs allocations - deny and force in shmem_enabled are equivalent to never and always for mmap(SHARED|ANON) but additionally override all tmpfs mounts so they act as if they were mounted with huge=never or huge=always Is that correct? If so, then I think it still makes sense to support per-size deny/force. Certainly if a per-size control is set to "inherit" and the top-level control is set to deny or force, you would need that to mean something. > >> Of course the huge= mount option would also need to take a per-size option in >> this case. e.g. huge=2048kB:advise,64kB:always > > IMO, I do not want to change the global 'huge=' mount option, which can control > both anon shmem and tmpfs, but mTHP now is only applied for anon shmem. So let's How does huge= control anon shmem? I thought it was only for mounted filesystems; so tmpfs? Perhaps my mental model for how this works is broken... > keep it be same with the global sysfs interface: > /sys/kernel/mm/transparent_hugepage/shmem_enabled. > > For tmpfs large folio strategy, I plan to address it later, and we may need more > discussion to determine if it should follow the file large folio strategy or not > (no investigation now). OK. But until you get to tmpfs, you'll need an interim definition for what it means if a per-size control is set to "inherit" and the top-level control is set to deny/force. > > Thanks for reviewing. No problem! Thanks for doing the work! > >>> TODO: >>>   - More testing and provide some performance data. >>>   - Need more discussion about the large folio allocation strategy for a >>> 'regular >>> file' operation created by memfd_create(), for example using ftruncate(fd) to >>> specify >>> the 'file' size, which need to follow the anonymous mTHP rule too? >>>   - Do not split the large folio when share memory swap out. >>>   - Can swap in a large folio for share memory. >>> >>> Baolin Wang (5): >>>    mm: memory: extend finish_fault() to support large folio >>>    mm: shmem: add an 'order' parameter for shmem_alloc_hugefolio() >>>    mm: shmem: add THP validation for PMD-mapped THP related statistics >>>    mm: shmem: add mTHP support for anonymous share pages >>>    mm: shmem: add anonymous share mTHP counters >>> >>>   include/linux/huge_mm.h |   4 +- >>>   mm/huge_memory.c        |   8 ++- >>>   mm/memory.c             |  25 +++++++--- >>>   mm/shmem.c              | 107 ++++++++++++++++++++++++++++++---------- >>>   4 files changed, 108 insertions(+), 36 deletions(-) >>>