From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-100.freemail.mail.aliyun.com (out30-100.freemail.mail.aliyun.com [115.124.30.100]) (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 1B714152186 for ; Fri, 31 May 2024 10:13:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.100 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717150391; cv=none; b=rK1QkXQghiADCqQQci/PJcKm3szqkwKZ8AKOomwfGv+iIIaj1++Xkg2bLsg54vp7tW7nA8jy3iS8wTW8DTJqOj0TSXa46S1Xrlga33M+jncitqIac4dQe2Wo0O4ycgYFGHNgWPEsRswl4NvJwSNvc9yn9fkgz88W6iitm6RsIiI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717150391; c=relaxed/simple; bh=QCtHZZ14X/rB1pYgsmDPVD/uninqZ3pM1vj5fz8+dkk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MX23Y+4hMyB+1a770H+WAcOLn/kfAcnaAmsfCpiAgOO9wzLHNoinurvtAglePpumIoYLOoKsRQhReuccMMOlaAUqZtQrcXKj1bbQrkKugqMSRogJOrzqxUtjAtaxztshOpVSqKeQUbsEvmvUOu/f8v7VUK01r8KM9/2fRWAMe1k= 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=J3sf852S; arc=none smtp.client-ip=115.124.30.100 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="J3sf852S" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1717150386; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=4u3Py3hl45dIuxCPAqHpFkSudYL9AInU3+rNe13UhMI=; b=J3sf852S7ea4wzm7ZgAG6FZwUAoGgAbnIuB8ryGPJ3djmRK4bZP78Av4vetAl3v4b1cDNN6pHi+GpSFbyr9Es+toLgLAX0yupIwfnbIZAb556q8ki6gpmeX9EyerxQpefZGqUqXrB5IeB79mItVUuziKG6jzYrMxMBYOUZDsSB8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037067113;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=15;SR=0;TI=SMTPD_---0W7ZXhau_1717150384; Received: from 30.97.56.62(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W7ZXhau_1717150384) by smtp.aliyun-inc.com; Fri, 31 May 2024 18:13:04 +0800 Message-ID: Date: Fri, 31 May 2024 18:13:03 +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: [PATCH v3 0/6] add mTHP support for anonymous shmem To: David Hildenbrand , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, ryan.roberts@arm.com, shy828301@gmail.com, ziy@nvidia.com, ioworker0@gmail.com, da.gomez@samsung.com, p.raghav@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/5/31 17:35, David Hildenbrand wrote: > On 30.05.24 04:04, 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 shmem 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. >> >> The primary strategy is similar to supporting anonymous mTHP. Introduce >> 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 new >> additional "inherit" option. By default all sizes will be set to "never" >> except PMD size, which is set to "inherit". This ensures backward >> compatibility >> with the anonymous shmem enabled of the top level, meanwhile also allows >> independent control of anonymous shmem enabled for each mTHP. >> >> Use the page fault latency tool to measure the performance of 1G >> anonymous shmem >> with 32 threads on my machine environment with: ARM64 Architecture, 32 >> cores, >> 125G memory: >> base: mm-unstable >> user-time    sys_time    faults_per_sec_per_cpu     faults_per_sec >> 0.04s        3.10s         83516.416                  2669684.890 >> >> mm-unstable + patchset, anon shmem mTHP disabled >> user-time    sys_time    faults_per_sec_per_cpu     faults_per_sec >> 0.02s        3.14s         82936.359                  2630746.027 >> >> mm-unstable + patchset, anon shmem 64K mTHP enabled >> user-time    sys_time    faults_per_sec_per_cpu     faults_per_sec >> 0.08s        0.31s         678630.231                 17082522.495 >> >>  From the data above, it is observed that the patchset has a minimal >> impact when >> mTHP is not enabled (some fluctuations observed during testing). When >> enabling 64K >> mTHP, there is a significant improvement of the page fault latency. > > Let me summarize the takeaway from the bi-weekly MM meeting as I > understood it, that includes Hugh's feedback on per-block tracking vs. Thanks David for the summarization. > mTHP: > > (1) Per-block tracking > > Per-block tracking is currently considered unwarranted complexity in > shmem.c. We should try to get it done without that. For any test cases > that fail, we should consider if they are actually valid for shmem. > > To optimize FALLOC_FL_PUNCH_HOLE for the cases where splitting+freeing > is not possible at fallcoate() time, detecting zeropages later and > retrying to split+free might be an option, without per-block tracking. > > (2) mTHP controls > > As a default, we should not be using large folios / mTHP for any shmem, > just like we did with THP via shmem_enabled. This is what this series > currently does, and is aprt of the whole mTHP user-space interface design. > > Further, the mTHP controls should control all of shmem, not only > "anonymous shmem". Yes, that's what I thought and in my TODO list. > > Also, we should properly fallback within the configured sizes, and not > jump "over" configured sizes. Unless there is a good reason. > > (3) khugepaged > > khugepaged needs to handle larger folios properly as well. Until fixed, > using smaller THP sizes as fallback might prohibit collapsing a > PMD-sized THP later. But really, khugepaged needs to be fixed to handle > that. > > (4) force/disable > > These settings are rather testing artifacts from the old ages. We should > not add them to the per-size toggles. We might "inherit" it from the > global one, though. Sorry, I missed this. So I thould remove the 'force' and 'deny' option for each mTHP, right? > > "within_size" might have value, and especially for consistency, we > should have them per size. > > > > So, this series only tackles anonymous shmem, which is a good starting > point. Ideally, we'd get support for other shmem (especially during > fault time) soon afterwards, because we won't be adding separate toggles > for that from the interface POV, and having inconsistent behavior > between kernel versions would be a bit unfortunate. > > > @Baolin, this series likely does not consider (4) yet. And I suggest we > have to take a lot of the "anonymous thp" terminology out of this > series, especially when it comes to documentation. Sure. I will remove the "anonymous thp" terminology from the documentation, but want to still keep it in the commit message, cause I want to start from the anonymous shmem. > > @Daniel, Pankaj, what are your plans regarding that? It would be great > if we could get an understanding on the next steps on !anon shmem. >