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s=arc-20220608; d=hostedemail.com; t=1713952875; a=rsa-sha256; cv=none; b=XaNlF3KlHiRiKHhMrG+9ePU3gqfQxCCOPMeuOQJ/RPPR4HxBDlcQc+XpP1wS9qm2oANTKQ cTOq1BYokaCQ39Bb9V2i8QDK/yIeZfQ7+jVrCademcJHLEHWOwpX+70QTQuPRrZzFVnc47 H5vFscWzWgSNIvTBfKA97/oSExDRMXU= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=none; spf=pass (imf19.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 DBE94339; Wed, 24 Apr 2024 03:01:41 -0700 (PDT) Received: from [10.1.25.156] (unknown [10.1.25.156]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BFE533F73F; Wed, 24 Apr 2024 03:01:12 -0700 (PDT) Message-ID: <5b8b22e7-6355-4b08-b5b5-1e33ebae6f16@arm.com> Date: Wed, 24 Apr 2024 11:01:11 +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> <80b5f87e-c156-4ccc-98f0-96f1fd864273@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 40D021A000C X-Stat-Signature: i1cpofj55b5abtgb8zq4bqonp6qchk6q X-HE-Tag: 1713952875-184895 X-HE-Meta: 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 Z6vjsrks waKfvunEW275pPuRW6brB+BjrJkFOL7vFdSe5uo5bF6DOlEj81me9DwD0GXk5exYTD3lq8raXnTPzfJzf+QZRGLIImANbDXA7eWz2HgjZAKlBTo6zsMIARlWuMWfXDnrAcK+vdeEHBeelVPKes2UTJHSghr0x6IGny7klshDZzA7skqk= 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 10:55, Baolin Wang wrote: > > > On 2024/4/24 16:26, Ryan Roberts wrote: >> 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 > > Correct. > >> 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. > > IMHO, the '/mm/transparent_hugepage/hugepage-XXkb/shmem_enabled' interface > should only control the anonymous shmem. And 'huge=' controls tmpfs allocation, > so we should not use anonymous control to override tmpfs control, which seems a > little mess? I agree it would be cleaner to only handle mmap(SHARED|ANON) here, and leave the tmpfs stuff for another time. But my point is that /mm/transparent_hugepage/shmem_enabled already interferes with tmpfs if the value is deny or force. So if you have: echo deny > /mm/transparent_hugepage/shmem_enabled echo inherit > /mm/transparent_hugepage/hugepage-64kB/shmem_enabled What does that mean? > >>>> 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... > > Sorry for noise, you are right. So this is still the reason I don't want to > change the semantics of 'huge=', which is used to control tmpfs. > >>> 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(-) >>>>>