From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 81625249F9 for ; Thu, 25 Apr 2024 06:20:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714026021; cv=none; b=Lst7OgkhFeg5BRh+0oR77k2Oq26PIzwI0QJCwfzthhAz7w7aW28AloXckhK+gs/OotuKeXTmcz/SPsBDsof0qNXvZQcE+Puguv/pKiw3Rq+LjR55yYkLEv4oKs7lITjr8Zz8uA4+5SiZH1V3QDpTVa6siVwpF+zEPD87pGEuFUI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714026021; c=relaxed/simple; bh=b2FXiK/eZeX/I3Uy3/f2pyW186iYyxkPDAjw64klGrw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oxxvD3D+dWjomEOEAaK/YwENZh381ZEFbj0pACEqPr1mYjkCLZ2edrkxmPJg+bUk2i/KuymOFI7occW2XKojGdjfLezXEE3QtukeLQ7C1dWBKSeE2VaYvOFMi+g44AVJcEB2EXtmFjdi+r64nezs+CJ4ReQvOK9HXXug5ECevrI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=Hh21TI8L; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="Hh21TI8L" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1714026015; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=xrJ1UEBMRIsaPvWFfYlp/8GNV4xLZP2PW8psa9EgH/U=; b=Hh21TI8LrpI7VRPFizWQRIGXOefhfrcCAh6ENOjzB0vVhuih49X/Bs1WQ2iz9s3lc7HGGJ7BNiyfcvkB7Y6803t76lKHwoQ+IL7FvwfCHkV+2yTcqa5+dOI56rB9CKOnfFpuXDcULqrESsCI3LwEMgaKRdN3+a9t63S9n2qleG8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R331e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045046011;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0W5EQGGR_1714026012; Received: from 30.97.56.61(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W5EQGGR_1714026012) by smtp.aliyun-inc.com; Thu, 25 Apr 2024 14:20:13 +0800 Message-ID: <8c0d6358-3c16-4a57-822c-04b3b3403fe6@linux.alibaba.com> Date: Thu, 25 Apr 2024 14:20:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/5] add mTHP support for anonymous share pages To: Ryan Roberts , 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> <5b8b22e7-6355-4b08-b5b5-1e33ebae6f16@arm.com> <813fe7fd-3004-4e8b-801d-95c33559a025@linux.alibaba.com> <76f816dd-3bbf-48c9-a630-3787051cf289@arm.com> From: Baolin Wang In-Reply-To: <76f816dd-3bbf-48c9-a630-3787051cf289@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/4/24 22:20, Ryan Roberts wrote: > On 24/04/2024 14:49, Baolin Wang wrote: >> >> >> On 2024/4/24 18:01, Ryan Roberts wrote: >>> 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 >> >> IIUC, this global control will cause shmem_is_huge() to always return false, so >> no matter how '/mm/transparent_hugepage/hugepage-xxxkB/shmem_enabled' is set, >> anonymous shmem will not use mTHP. No? > > No, that's not how '/mm/transparent_hugepage/hugepage-xxxkB/enabled' works, and > I think '/mm/transparent_hugepage/hugepage-xxxkB/shmem_enabled' should follow > the established pattern. > > For anon-private, each size is controlled by its > /mm/transparent_hugepage/hugepage-xxxkB/enabled value. Unless that value is > "inherit", in which case the value in /mm/transparent_hugepage/enabled is used > for that size. > > That approach enables us to 1) maintain back-compat and 2) control each size > independently > > 1) is met because the default is that all sizes are initially set to "never", > except the PMD-size (e.g. /mm/transparent_hugepage/hugepage-2048kB/enabled) > which is initially set to inherit. So any mTHP unaware SW can still modify > /mm/transparent_hugepage/enabled and it will still only apply to PMD size. > > 2) is met because mTHP aware SW can come along and e.g. enable the 64K size > (echo always > /mm/transparent_hugepage/hugepage-64kB/enabled) without having to > modify the value in /mm/transparent_hugepage/enabled. Thanks for explanation. Initially, I want to make ‘/mm/transparent_hugepage/shmem_enabled’ be a global control for huge page, but I think it should follow the same strategy as anon mTHP as you said. >>> echo inherit > /mm/transparent_hugepage/hugepage-64kB/shmem_enabled >>> >>> What does that mean? > > So I think /mm/transparent_hugepage/hugepage-xxxkB/shmem_enabled will need to > support the deny and force values. When applied to non-PMD sizes, "deny" can > just be a noop for now, because there was no way to configure a tmpfs mount for > non-PMD size THP in the first place. But I'm not sure what to do with "force"? OK. And I also prefer that "force" should be a noop too, since anon shmem control should not configure tmpfs huge page allocation.