From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-118.freemail.mail.aliyun.com (out30-118.freemail.mail.aliyun.com [115.124.30.118]) (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 2DE3613A87C for ; Tue, 22 Oct 2024 03:41:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.118 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729568484; cv=none; b=RXVgrSg4KplEHLuUk08rjKCsrR8fGGIJ53SLXp/tZkWZ51RvyI0gSIUkJBp6pt8moojoRx+Efs1ijbs6V5D8tXK5DNBrOsDEEgqnG21cWJRI7Wbv9vdslOhkqsyEJT6kQa8tuP+gqge4BSXgZusxe2MRjTw1W/9mrIoElyeJYag= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729568484; c=relaxed/simple; bh=maImKSs5V0zrt3tR8/oK0L6o2lpOfcXOPtCYebmGRB4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LEKmUjFlAXabytyOeOmo+pWXRWY//q/3EJDhUxdTgXZFOsuuQt7Pdq67hFoV7QfgMQfHvd/YAaqkT8vgYIQMiUTWrCIjXOlC2CBQtaltqZ3RQoI8b/NsyEXvkKj7u5wC24sSFV+oH6nHnaxIPvsVY+Zubl8jzUwU1I1EkkuW6ak= 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=ipcqEc6V; arc=none smtp.client-ip=115.124.30.118 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="ipcqEc6V" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1729568471; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=PObwzHJJIeFT+P4LK3JrB627zhyrly0VUYXDLNen+YQ=; b=ipcqEc6VJ5C8SPJdJu6KbIjTPxNFCQXcKogyH8oyNegwtq8+vX8qJnXO48sreyZkFqlgOnvVHLUVLWsp986rBEZyUCgXNc7Q7UK0TREWTyPOdWmi9Vhlvv+tud7FgltHcVIOAnCcRah5Z31QWbq0DqEflbY4U1WFVpE0sYGB8H8= Received: from 30.74.144.133(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WHgJnN7_1729568469 cluster:ay36) by smtp.aliyun-inc.com; Tue, 22 Oct 2024 11:41:09 +0800 Message-ID: Date: Tue, 22 Oct 2024 11:41:08 +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: Daniel Gomez , "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, 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 21:34, Daniel Gomez wrote: > On Mon Oct 21, 2024 at 10:54 AM CEST, 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. >> >>>> 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. > > I think moving tmpfs to allocate large folios opportunistically by > default (as it was proposed initially) doesn't necessary conflict with > the default behaviour (huge=never). We just need to clarify that in > the documentation. > > However, and IIRC, one of the requests from Hugh was to have a way to > disable large folios which is something other FS do not have control > of as of today. Ryan sent a proposal to actually control that globally > but I think it didn't move forward. So, what are we missing to go back > to implement large folios in tmpfs in the default case, as any other fs > leveraging large folios? IMHO, as I discussed with Kirill, we still need maintain compatibility with the 'huge=' mount option. This means that if 'huge=never' is set for tmpfs, huge page allocation will still be prohibited (which can address Hugh's request?). However, if 'huge=' is not set, we can allocate large folios based on the write size.