From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C26DFC433E1 for ; Fri, 21 Aug 2020 02:59:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 73A642076E for ; Fri, 21 Aug 2020 02:59:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73A642076E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BCDAD8D0030; Thu, 20 Aug 2020 22:59:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B58148D002F; Thu, 20 Aug 2020 22:59:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9D1858D0030; Thu, 20 Aug 2020 22:59:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0066.hostedemail.com [216.40.44.66]) by kanga.kvack.org (Postfix) with ESMTP id 847AB8D002F for ; Thu, 20 Aug 2020 22:59:16 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 34F6A2AAE for ; Fri, 21 Aug 2020 02:59:16 +0000 (UTC) X-FDA: 77173069512.15.feast76_060ce2827035 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 090771814B0C1 for ; Fri, 21 Aug 2020 02:59:16 +0000 (UTC) X-HE-Tag: feast76_060ce2827035 X-Filterd-Recvd-Size: 6447 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by imf06.hostedemail.com (Postfix) with ESMTP for ; Fri, 21 Aug 2020 02:59:14 +0000 (UTC) IronPort-SDR: LMVqJTzWZB2pdpdR+rgUZ6kNckn2RS0ZL2NEyqFvKtVY3Ls6bJhtfZdoVFgGysm0tGeAEIs5mC b/5u6/DTGo3w== X-IronPort-AV: E=McAfee;i="6000,8403,9719"; a="240268648" X-IronPort-AV: E=Sophos;i="5.76,335,1592895600"; d="scan'208";a="240268648" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Aug 2020 19:59:13 -0700 IronPort-SDR: HsHkPk12FpU091H67hyVGHN+fyXnU1tcswRmp+L1e70WC0Lg2cctbfTvjmT+Ak6sDZ/MBN7emc G75NVWkkyjmA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.76,335,1592895600"; d="scan'208";a="293693132" Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.164]) by orsmga003.jf.intel.com with ESMTP; 20 Aug 2020 19:59:09 -0700 From: "Huang\, Ying" To: Dave Chinner Cc: Gao Xiang , Andrew Morton , , , Carlos Maiolino , Eric Sandeen , Yang Shi , Rafael Aquini , stable Subject: Re: [PATCH v2] mm, THP, swap: fix allocating cluster for swapfile by mistake References: <20200820045323.7809-1-hsiangkao@redhat.com> <20200820233446.GB7728@dread.disaster.area> <20200821002145.GA28298@xiangao.remote.csb> <20200821010330.GC7728@dread.disaster.area> Date: Fri, 21 Aug 2020 10:59:08 +0800 In-Reply-To: <20200821010330.GC7728@dread.disaster.area> (Dave Chinner's message of "Fri, 21 Aug 2020 11:03:30 +1000") Message-ID: <87mu2ovh4z.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: 090771814B0C1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Dave Chinner writes: > On Fri, Aug 21, 2020 at 08:21:45AM +0800, Gao Xiang wrote: >> Hi Dave, >> >> On Fri, Aug 21, 2020 at 09:34:46AM +1000, Dave Chinner wrote: >> > On Thu, Aug 20, 2020 at 12:53:23PM +0800, Gao Xiang wrote: >> > > SWP_FS is used to make swap_{read,write}page() go through >> > > the filesystem, and it's only used for swap files over >> > > NFS. So, !SWP_FS means non NFS for now, it could be either >> > > file backed or device backed. Something similar goes with >> > > legacy SWP_FILE. >> > > >> > > So in order to achieve the goal of the original patch, >> > > SWP_BLKDEV should be used instead. >> > > >> > > FS corruption can be observed with SSD device + XFS + >> > > fragmented swapfile due to CONFIG_THP_SWAP=y. >> > > >> > > I reproduced the issue with the following details: >> > > >> > > Environment: >> > > QEMU + upstream kernel + buildroot + NVMe (2 GB) >> > > >> > > Kernel config: >> > > CONFIG_BLK_DEV_NVME=y >> > > CONFIG_THP_SWAP=y >> > >> > Ok, so at it's core this is a swap file extent versus THP swap >> > cluster alignment issue? >> >> I think yes. >> >> > >> > > diff --git a/mm/swapfile.c b/mm/swapfile.c >> > > index 6c26916e95fd..2937daf3ca02 100644 >> > > --- a/mm/swapfile.c >> > > +++ b/mm/swapfile.c >> > > @@ -1074,7 +1074,7 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size) >> > > goto nextsi; >> > > } >> > > if (size == SWAPFILE_CLUSTER) { >> > > - if (!(si->flags & SWP_FS)) >> > > + if (si->flags & SWP_BLKDEV) >> > > n_ret = swap_alloc_cluster(si, swp_entries); >> > > } else >> > > n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE, >> > >> > IOWs, if you don't make this change, does the corruption problem go >> > away if you align swap extents in iomap_swapfile_add_extent() to >> > (SWAPFILE_CLUSTER * PAGE_SIZE) instead of just PAGE_SIZE? >> > >> > I.e. if the swapfile extents are aligned correctly to huge page swap >> > cluster size and alignment, does the swap clustering optimisations >> > for swapping THP pages work correctly? And, if so, is there any >> > performance benefit we get from enabling proper THP swap clustering >> > on swapfiles? >> > >> >> Yeah, I once think about some similiar thing as well. My thought for now is >> >> - First, SWAP THP doesn't claim to support such swapfile for now. >> And the original author tried to explicitly avoid the whole thing in >> >> f0eea189e8e9 ("mm, THP, swap: Don't allocate huge cluster for file backed swap device") >> >> So such thing would be considered as some new feature and need >> more testing at least. But for now I think we just need a quick >> fix to fix the commit f0eea189e8e9 to avoid regression and for >> backport use. > > Sure, a quick fix is fine for the current issue. I'm asking > questions about the design/architecture of how THP_SWAP is supposed > to work and whether swapfiles are violating some other undocumented > assumption about swapping THP files... The main requirement for THP_SWAP is that the swap cluster need to be mapped to the continuous block device space. So Yes. In theory, it's possible to support THP_SWAP for swapfile. But I don't know whether people need it or not. Best Regards, Huang, Ying >> - It is hard for users to control swapfile in >> SWAPFILE_CLUSTER * PAGE_SIZE extents, especially users' >> disk are fragmented or have some on-disk metadata limitation or >> something. It's very hard for users to utilize this and arrange >> their swapfile physical addr alignment and fragments for now. > > This isn't something users control. The swapfile extent mapping code > rounds the swap extents inwards so that the parts of the on-disk > extents that are not aligned or cannot hold a full page are > omitted from the ranges of the file that can be swapped to. > > i.e. a file that extents aligned to 4kB is fine for a 4KB page size > machine, but needs additional alignment to allow swapping to work on > a 64kB page size machine. Hence the swap code rounds the file > extents inwards to PAGE_SIZE to align them correctly. We really > should be doing this for THP page size rather than PAGE_SIZE if > THP_SWAP is enabled, regardless of whether swap clustering is > enabled or not... > > Cheers, > > Dave.