From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) (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 71B50203706 for ; Tue, 8 Jul 2025 07:54:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751961245; cv=none; b=Zsste9PJUT1COZ7XyUANM18FagdGgpBlZCLgg/cRL3FP1zY0dU9n+55BkxP/X//ZTn/M/ohoW4VognAX6XG07nIm47iRINfMNVxToYs9gvo7GOV2lh9YaMHvUTgBl9CfBrJwE7bcknk7T2w4Dmcb+GC4O6B4xnA9meNV3JYNGaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751961245; c=relaxed/simple; bh=Y0uxjOZKAIehwxOwZRu+r+eyUc2ebvQ/3q0wvD36E0Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z8fAokGBZL8BC8hJc2ltDz0mLc/JjrrW1lppwux2DzLT//XC/CgrgVfXnTspgjAxDYILqHlvF8ocAZwqjjAusQjT8+WyWSxuqJT/ON86kVN3IIqhN6S3tLBV0E+fuBspNFc2pvqFun/RZu3QRIm064OvGyorimgylM+jeGcfc/I= 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=mNy2f5P5; arc=none smtp.client-ip=115.124.30.112 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="mNy2f5P5" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1751961239; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=DNfi3XvvaPQFWN6RIuvca87fevIPOyq+CtUUka0qa+g=; b=mNy2f5P5NEUV540Ng+TQkuzQdtWSBcfol28wgWsfSADKf6T3629medG5kJhQIS5da+aBv3UQs6LrC7zFMz1bCPn+qSkhusiPcAju07BK+apr3ftVCHxwR+XJEtcB5hYw5WXOv3ZVLzJU+OB/Pf8Dw0CkzNGI3Z8oKG1D4WPJX60= Received: from 30.74.144.119(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WiLpkEF_1751961236 cluster:ay36) by smtp.aliyun-inc.com; Tue, 08 Jul 2025 15:53:57 +0800 Message-ID: <23f1c3ab-16ca-41db-b008-22448d9e08f2@linux.alibaba.com> Date: Tue, 8 Jul 2025 15:53:56 +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 v2] mm: fault in complete folios instead of individual pages for tmpfs To: Lorenzo Stoakes Cc: Andrew Morton , hughd@google.com, david@redhat.com, ziy@nvidia.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <440940e78aeb7430c5cc8b6d2088ae98265b9809.1751599072.git.baolin.wang@linux.alibaba.com> <20250704151858.73d35a24b4c2f53bdb0c1b85@linux-foundation.org> <4c055849-d7dd-4b9f-9666-fcb0bccf8681@linux.alibaba.com> <007c4a94-c94a-418e-9907-7510422f8ca4@lucifer.local> From: Baolin Wang In-Reply-To: <007c4a94-c94a-418e-9907-7510422f8ca4@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/7/7 21:33, Lorenzo Stoakes wrote: > On Sun, Jul 06, 2025 at 10:02:35AM +0800, Baolin Wang wrote: >> >> >> On 2025/7/5 06:18, Andrew Morton wrote: >>> On Fri, 4 Jul 2025 11:19:26 +0800 Baolin Wang wrote: >>> >>>> After commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs"), >>>> tmpfs can also support large folio allocation (not just PMD-sized large >>>> folios). >>>> >>>> However, when accessing tmpfs via mmap(), although tmpfs supports large folios, >>>> we still establish mappings at the base page granularity, which is unreasonable. >>>> >>>> We can map multiple consecutive pages of a tmpfs folios at once according to >>>> the size of the large folio. On one hand, this can reduce the overhead of page >>>> faults; on the other hand, it can leverage hardware architecture optimizations >>>> to reduce TLB misses, such as contiguous PTEs on the ARM architecture. >>>> >>>> Moreover, tmpfs mount will use the 'huge=' option to control large folio >>>> allocation explicitly. So it can be understood that the process's RSS statistics >>>> might increase, and I think this will not cause any obvious effects for users. >>>> >>>> Performance test: >>>> I created a 1G tmpfs file, populated with 64K large folios, and write-accessed it >>>> sequentially via mmap(). I observed a significant performance improvement: >>> >>> That doesn't sound like a crazy thing to do. >>> >>>> Before the patch: >>>> real 0m0.158s >>>> user 0m0.008s >>>> sys 0m0.150s >>>> >>>> After the patch: >>>> real 0m0.021s >>>> user 0m0.004s >>>> sys 0m0.017s >>> >>> And look at that. >>> >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index 0f9b32a20e5b..9944380e947d 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>>> @@ -5383,10 +5383,10 @@ vm_fault_t finish_fault(struct vm_fault *vmf) >>>> /* >>>> * Using per-page fault to maintain the uffd semantics, and same >>>> - * approach also applies to non-anonymous-shmem faults to avoid >>>> + * approach also applies to non shmem/tmpfs faults to avoid >>>> * inflating the RSS of the process. >>>> */ >>>> - if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma)) || >>>> + if (!vma_is_shmem(vma) || unlikely(userfaultfd_armed(vma)) || >>>> unlikely(needs_fallback)) { >>>> nr_pages = 1; >>>> } else if (nr_pages > 1) { >>> >>> and that's it? >>> >>> I'm itching to get this into -stable, really. What LTS user wouldn't >>> want this? >> >> This is an improvement rather than a bugfix, so I don't think it needs to go >> into LTS. >> >> Could it be viewed as correcting an oversight in >>> acd7ccb284b8? >> >> Yes, I should have added this optimization in the series of the commit >> acd7ccb284b8. But obviously, I missed this :(. > > Buuut if this was an oversight for that patch that causes an unnecessary > perf degradation, surely this should have fixes tag + cc stable no? IMO, this commit acd7ccb284b8 won't cause perf degradation, instead it is used to introduce a new feature, while the current patch is a further reasonable optimization. As I mentioned, this is an improvement, not a bugfix or a patch to address performance regression.