From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) (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 4F39E2110E for ; Tue, 22 Oct 2024 03:34:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729568062; cv=none; b=C4TvG39g+mEjn1aysS8dI2NtFfqMVkOrtCxOyZKFnFA09TKtAqDd8pvnm2PFVA2OXtGcSn5kgfDgdCFDrtyObzKFOjq+4MpmsCJdDQySi6avPxyfptMPmBgMKjlDFtILz1Osk8tChpaULIq8DyDFs7ClNJ2PZXU78syeG+L0+5M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729568062; c=relaxed/simple; bh=NvFcoLdO5B5977/kT1+5tyV9WhPQYWvFCEpuTO+c70s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=R0d4xfhAwSI1hHEmQvaPiW7kPZO8KcDEClisZ0qoPq+sqH8m5yy5wyN6EidgMZr8yv1joYAhVfEQWg8L3Rncm1Zfi9VQJFzZSWFgFh9MWmlNvCq4SwoHGbhZ71Jk6gMumRAwTvWMz8F1joLUKT36tlMPSdYcrDCc9mQPahrDMdQ= 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=iyqrztnD; arc=none smtp.client-ip=115.124.30.124 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="iyqrztnD" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1729568057; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=+mCA/Ku9P9aJGHHaHesY9FGYchTbxDumxyCuDvQcJT4=; b=iyqrztnDCklLE8nmSupMzvQI36oAdAjmyey3vqAD7oPsKsGodnP+DlrT9M22UFEhS4RIRH2w7pizOVo7QnVPLa9wm6XBQqmgwWaEaGFlb+M3xTe5XqPytXvMHMbI9pDbXPGTpKimvFxIBJKW4J0iS7h1OgnDZOWjwuc/JGaEpc0= Received: from 30.74.144.133(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WHgRv3t_1729568054 cluster:ay36) by smtp.aliyun-inc.com; Tue, 22 Oct 2024 11:34:15 +0800 Message-ID: <2c6b7456-8846-44b0-8e58-158c480aaead@linux.alibaba.com> Date: Tue, 22 Oct 2024 11:34:14 +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 v3 0/4] Support large folios for tmpfs To: "Kirill A. Shutemov" Cc: Matthew Wilcox , akpm@linux-foundation.org, hughd@google.com, david@redhat.com, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ryan.roberts@arm.com, ioworker0@gmail.com, da.gomez@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" References: <6dohx7zna7x6hxzo4cwnwarep3a7rohx4qxubds3uujfb7gp3c@2xaubczl2n6d> <8e48cf24-83e1-486e-b89c-41edb7eeff3e@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/10/21 16:54, Kirill A. Shutemov wrote: > On Mon, Oct 21, 2024 at 02:24:18PM +0800, Baolin Wang wrote: >> >> >> On 2024/10/17 19:26, Kirill A. Shutemov wrote: >>> On Thu, Oct 17, 2024 at 05:34:15PM +0800, Baolin Wang wrote: >>>> + Kirill >>>> >>>> On 2024/10/16 22:06, Matthew Wilcox wrote: >>>>> On Thu, Oct 10, 2024 at 05:58:10PM +0800, Baolin Wang wrote: >>>>>> Considering that tmpfs already has the 'huge=' option to control the THP >>>>>> allocation, it is necessary to maintain compatibility with the 'huge=' >>>>>> option, as well as considering the 'deny' and 'force' option controlled >>>>>> by '/sys/kernel/mm/transparent_hugepage/shmem_enabled'. >>>>> >>>>> No, it's not. No other filesystem honours these settings. tmpfs would >>>>> not have had these settings if it were written today. It should simply >>>>> ignore them, the way that NFS ignores the "intr" mount option now that >>>>> we have a better solution to the original problem. >>>>> >>>>> To reiterate my position: >>>>> >>>>> - When using tmpfs as a filesystem, it should behave like other >>>>> filesystems. >>>>> - When using tmpfs to implement MAP_ANONYMOUS | MAP_SHARED, it should >>>>> behave like anonymous memory. >>>> >>>> I do agree with your point to some extent, but the ‘huge=’ option has >>>> existed for nearly 8 years, and the huge orders based on write size may not >>>> achieve the performance of PMD-sized THP in some scenarios, such as when the >>>> write length is consistently 4K. So, I am still concerned that ignoring the >>>> 'huge' option could lead to compatibility issues. >>> >>> Yeah, I don't think we are there yet to ignore the mount option. >> >> OK. >> >>> Maybe we need to get a new generic interface to request the semantics >>> tmpfs has with huge= on per-inode level on any fs. Like a set of FADV_* >>> handles to make kernel allocate PMD-size folio on any allocation or on >>> allocations within i_size. I think this behaviour is useful beyond tmpfs. >>> >>> Then huge= implementation for tmpfs can be re-defined to set these >>> per-inode FADV_ flags by default. This way we can keep tmpfs compatible >>> with current deployments and less special comparing to rest of >>> filesystems on kernel side. >> >> I did a quick search, and I didn't find any other fs that require PMD-sized >> huge pages, so I am not sure if FADV_* is useful for filesystems other than >> tmpfs. Please correct me if I missed something. > > What do you mean by "require"? THPs are always opportunistic. > > IIUC, we don't have a way to hint kernel to use huge pages for a file on > read from backing storage. Readahead is not always the right way. IIUC, most file systems use method similar to iomap buffered IO (see iomap_get_folio()) to allocate huge pages. What I mean is that, it would be better to have a real use case to add a hint for allocating THP (other than tmpfs). >>> If huge= is not set, tmpfs would behave the same way as the rest of >>> filesystems. >> >> So if 'huge=' is not set, tmpfs write()/fallocate() can still allocate large >> folios based on the write size? If yes, that means it will change the >> default huge behavior for tmpfs. Because previously having 'huge=' is not >> set means the huge option is 'SHMEM_HUGE_NEVER', which is similar to what I >> mentioned: >> "Another possible choice is to make the huge pages allocation based on write >> size as the *default* behavior for tmpfs, ..." > > I am more worried about breaking existing users of huge pages. So changing > behaviour of users who don't specify huge is okay to me. OK. Good.