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=-12.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 5BD9AC33CB2 for ; Tue, 14 Jan 2020 14:36:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 227EC24683 for ; Tue, 14 Jan 2020 14:36:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579012585; bh=6cgZGxZ4TavF4DzZ2Kn7H5hN65Uua64pqMp/PYHU7qQ=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=T94kZuf2QzsdCv+UY/d+VKbGhrrF+Iq5Ybe6D/xdKyUWYliv6JRrhjmq2o4Cu2z6Y 6+PWPkwaS9RelBuHpNZZYwIwlxRNOJLD8maCigYWL9sGBzwZfSHOfxLj/cG+k9nLcS bpjNBNuDQcgwgcSYICXzGfq3cmgXwcebdOXZ7Tsw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727289AbgANOgX (ORCPT ); Tue, 14 Jan 2020 09:36:23 -0500 Received: from mail.kernel.org ([198.145.29.99]:48010 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726115AbgANOgX (ORCPT ); Tue, 14 Jan 2020 09:36:23 -0500 Received: from mail-vs1-f47.google.com (mail-vs1-f47.google.com [209.85.217.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D121F2467D; Tue, 14 Jan 2020 14:36:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579012582; bh=6cgZGxZ4TavF4DzZ2Kn7H5hN65Uua64pqMp/PYHU7qQ=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=VNqABQjX0XGSMHpI5bSQIxKEmIpWrFy6DwKiPJzi4Zgfz4Shp+Cxj3rKhg6n8rkBd pZDcusaSChnZTu/qF88fWlzZzOtNq63rcU/BmcONtDBPYZmj0DU34baonUDyFRuZPK pRuz+WiixACDehrSmQ4O4GbZmW7uTWXdsxR8ILhA= Received: by mail-vs1-f47.google.com with SMTP id s16so8324696vsc.10; Tue, 14 Jan 2020 06:36:21 -0800 (PST) X-Gm-Message-State: APjAAAXve5RsNXbASpfYFc3N11A/Rm0Q5iRRMX77MCV9dnhBTG8SOYMh YkSD3a+czIpuMfoF144hlzFPdCSjoEiEK8dS1Ds= X-Google-Smtp-Source: APXvYqw3E77CcPD7PJWzNpgOU4PGzwiob4S3qlUZlRL7Ci+FJrSm/SBt/exsYZpF9EOTbroq1yuxIWfKwV7VO1Z9OF4= X-Received: by 2002:a67:8010:: with SMTP id b16mr1549481vsd.90.1579012580656; Tue, 14 Jan 2020 06:36:20 -0800 (PST) MIME-Version: 1.0 References: <20191216182656.15624-1-fdmanana@kernel.org> <20191216182656.15624-2-fdmanana@kernel.org> <20200107175739.GC472651@magnolia> <20200108161536.GC5552@magnolia> <20200109191201.GC8247@magnolia> In-Reply-To: <20200109191201.GC8247@magnolia> From: Filipe Manana Date: Tue, 14 Jan 2020 14:36:09 +0000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] fs: allow deduplication of eof block into the end of the destination file To: "Darrick J. Wong" Cc: linux-fsdevel , linux-btrfs , xfs , Filipe Manana , Alexander Viro Content-Type: text/plain; charset="UTF-8" Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Thu, Jan 9, 2020 at 7:12 PM Darrick J. Wong wrote: > > On Thu, Jan 09, 2020 at 07:00:09PM +0000, Filipe Manana wrote: > > On Wed, Jan 8, 2020 at 4:15 PM Darrick J. Wong wrote: > > > > > > On Wed, Jan 08, 2020 at 11:36:04AM +0000, Filipe Manana wrote: > > > > On Tue, Jan 7, 2020 at 5:57 PM Darrick J. Wong wrote: > > > > > > > > > > On Tue, Jan 07, 2020 at 04:23:15PM +0000, Filipe Manana wrote: > > > > > > On Mon, Dec 16, 2019 at 6:28 PM wrote: > > > > > > > > > > > > > > From: Filipe Manana > > > > > > > > > > > > > > We always round down, to a multiple of the filesystem's block size, the > > > > > > > length to deduplicate at generic_remap_check_len(). However this is only > > > > > > > needed if an attempt to deduplicate the last block into the middle of the > > > > > > > destination file is requested, since that leads into a corruption if the > > > > > > > length of the source file is not block size aligned. When an attempt to > > > > > > > deduplicate the last block into the end of the destination file is > > > > > > > requested, we should allow it because it is safe to do it - there's no > > > > > > > stale data exposure and we are prepared to compare the data ranges for > > > > > > > a length not aligned to the block (or page) size - in fact we even do > > > > > > > the data compare before adjusting the deduplication length. > > > > > > > > > > > > > > After btrfs was updated to use the generic helpers from VFS (by commit > > > > > > > 34a28e3d77535e ("Btrfs: use generic_remap_file_range_prep() for cloning > > > > > > > and deduplication")) we started to have user reports of deduplication > > > > > > > not reflinking the last block anymore, and whence users getting lower > > > > > > > deduplication scores. The main use case is deduplication of entire > > > > > > > files that have a size not aligned to the block size of the filesystem. > > > > > > > > > > > > > > We already allow cloning the last block to the end (and beyond) of the > > > > > > > destination file, so allow for deduplication as well. > > > > > > > > > > > > > > Link: https://lore.kernel.org/linux-btrfs/2019-1576167349.500456@svIo.N5dq.dFFD/ > > > > > > > Signed-off-by: Filipe Manana > > > > > > > > > > > > Darrick, Al, any feedback? > > > > > > > > > > Is there a fstest to check for correct operation of dedupe at or beyond > > > > > source and destfile EOF? Particularly if one range is /not/ at EOF? > > > > > > > > Such as what generic/158 does already? > > > > > > Urk, heh. :) > > > > > > > > And that an mmap read of the EOF block will see zeroes past EOF before > > > > > and after the dedupe operation? > > > > > > > > Can you elaborate a bit more? Why an mmap read and not a buffered or a > > > > direct IO read before and after deduplication? > > > > Is there anything special for the mmap reads on xfs, is that your > > > > concern? Or is the idea to deduplicate while the file is mmap'ed? > > > > > > I cite mmap reads past EOF specifically because unlike buffered/direct > > > reads where the VFS will stop reading exactly at EOF, a memory mapping > > > maps in an entire memory page, and the fs is supposed to ensure that the > > > bytes past EOF are zeroed. > > > > Ok, on btrfs we zero out the rest of the page both in for all reads. > > > > So, it's not problem: > > > > $ file_size=$((64 * 1024 + 500)) > > $ xfs_io -f -c "pwrite -S 0xba 0 $file_size" foo > > $ xfs_io -f -c "pwrite -S 0xba 0 $file_size" bar > > $ sync > > > > $ xfs_io -c "mmap 0 68K" -c "mread -v 0 68K" -c "dedupe bar 0 0 > > $file_size" -c "mread -v 0 68K" foo > > > > Both mreads returns exactly the same, eof is still the same and all > > bytes after it have a value of 0. > > > > This is the same as it is for cloning. > > Oh good. :) > > > > > > > Hm now that I look at g/158 it doesn't actually verify mmap reads. I > > > looked around and can't really see anything that checks mmap reads > > > before and after a dedupe operation at EOF. > > > > > > > > If I fallocate a 16k file, write 'X' into the first 5000 bytes, > > > > > write 'X' into the first 66,440 bytes (60k + 5000) of a second file, and > > > > > then try to dedupe (first file, 0-8k) with (second file, 60k-68k), > > > > > should that work? > > > > > > > > You haven't mentioned the size of the second file, nor if the first > > > > file has a size of 16K which I assume (instead of fallocate with the > > > > keep size flag). > > > > > > Er, sorry, yes. The first file is 16,384 bytes long; the second file is > > > 66,440 bytes. > > > > > > > Anyway, I assume you actually meant to dedupe the range 0 - 5000 from > > > > the first file into the range 60k - 60k + 5000 of the second file, and > > > > that the second file has a size of 60k + 5000. > > > > > > Nope, I meant to say to dedupe the range (offset: 0, length: 8192) from > > > the first file into the second file (offset: 61440, length: 8192). The > > > source range is entirely below EOF, and the dest range ends right at > > > EOF in the second file. > > > > The dedupe operations fails with -EINVAL, both before and after this patch, > > since the whenever one of ranges crosses eof, we must fail dedupe with -EINVAL. > > This happens at generic_remap_checks(), which called before > > generic_remap_check_len(). > > > > This is no different from the other existing tests in fstests, which > > cover this case already. > > Ah, ok. > > > > > If so, that fails with -EINVAL because the source range is not block > > > > size aligned, and we already have generic fstests that test attempt to > > > > duplication and clone non-aligned ranges that don't end at eof. > > > > This patch doesn't change that behaviour, it only aims to allow > > > > deduplication of the eof block of the source file into the eof of the > > > > destination file. > > > > > > > > > > > > > > > > > > I'm convinced that we could support dedupe to EOF when the ranges of the > > > > > two files both end at the respective file's EOF, but it's the weirder > > > > > corner cases that I worry about... > > > > > > > > Well, we used to do that in btrfs before migrating to the generic code. > > > > Since I discovered the corruption due to deduplication of the eof > > > > block into the middle of a file in 2018's summer, the btrfs fix > > > > allowed deduplication of the eof block only if the destination end > > > > offset matched the eof of the destination file: > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=de02b9f6bb65a6a1848f346f7a3617b7a9b930c0 > > > > > > > > Since then no issues were found nor users reported any problems so far. > > > > > > I'm ok with that one scenario, it's the "one range ends at eof, > > > the other doesn't" case that I'm picking on. :) > > > > > > (Another way to shut me up would be to run generic/52[12] with > > > TIME_FACTOR=1000 (i.e. 1 billion fsx ops) and see what comes exploding > > > out. :)) > > > > Well, it will take nearly 2 weeks to get those tests to complete with > > 1 billion ops, taking into > > account each takes around 500 seconds to run here (on xfs) with 1 > > million operations... > > I know. I probably should have clarified: every month or two I build a > kernel from tip, throw it in a VM, and let it run for however long it > goes until it dies, fixing whatever problems as I find them. > > *So far* no billionaire plutocrats have complained about the huge > compute bills that are probably racking up. ;) > > (FWIW I also tossed your patch onto another one of these VMs and it > hasn't died yet, so that's probably an ok sign) For 100 million ops, on 5.5-rc5 kernel with this patchset and on xfs: $ TIME_FACTOR=100 MKFS_OPTIONS="-m reflink=1,rmapbt=1" ./check generic/521 generic/522 FSTYP -- xfs (debug) PLATFORM -- Linux/x86_64 debian5 5.5.0-rc5-btrfs-next-67 #1 SMP PREEMPT Thu Jan 9 13:48:07 WET 2020 MKFS_OPTIONS -- -f -m reflink=1,rmapbt=1 /dev/sdc MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1 generic/521 482s ... 48961s generic/522 536s ... 54432s Ran: generic/521 generic/522 Passed all 2 tests Similar for btrfs, no problems found (yet at least). Thanks. > > > > > > > > Any other specific test you would like to see? > > > > > > No, just that. And mmap reads. :) > > > > Given that we allow cloning of eof into eof already (and that doesn't > > cause any known problems), > > I don't see why you are so concerned with allowing dedupe to behave the same. > > > > The only thing I can see it could be a problem would be comparing the > > contents of the last page beyond the eof position, > > but as stated on the changelog, it's not a problem since we call > > vfs_dedupe_file_range_compare() before we > > round down the length at generic_remap_check_len() - the data compare > > function already has the correct behaviour. > > > > --D > > > Thanks. > > > > > > > > --D > > > > > > > Thanks. > > > > > > > > > > > > > > --D > > > > > > > > > > > Thanks. > > > > > > > > > > > > > --- > > > > > > > fs/read_write.c | 10 ++++------ > > > > > > > 1 file changed, 4 insertions(+), 6 deletions(-) > > > > > > > > > > > > > > diff --git a/fs/read_write.c b/fs/read_write.c > > > > > > > index 5bbf587f5bc1..7458fccc59e1 100644 > > > > > > > --- a/fs/read_write.c > > > > > > > +++ b/fs/read_write.c > > > > > > > @@ -1777,10 +1777,9 @@ static int remap_verify_area(struct file *file, loff_t pos, loff_t len, > > > > > > > * else. Assume that the offsets have already been checked for block > > > > > > > * alignment. > > > > > > > * > > > > > > > - * For deduplication we always scale down to the previous block because we > > > > > > > - * can't meaningfully compare post-EOF contents. > > > > > > > - * > > > > > > > - * For clone we only link a partial EOF block above the destination file's EOF. > > > > > > > + * For clone we only link a partial EOF block above or at the destination file's > > > > > > > + * EOF. For deduplication we accept a partial EOF block only if it ends at the > > > > > > > + * destination file's EOF (can not link it into the middle of a file). > > > > > > > * > > > > > > > * Shorten the request if possible. > > > > > > > */ > > > > > > > @@ -1796,8 +1795,7 @@ static int generic_remap_check_len(struct inode *inode_in, > > > > > > > if ((*len & blkmask) == 0) > > > > > > > return 0; > > > > > > > > > > > > > > - if ((remap_flags & REMAP_FILE_DEDUP) || > > > > > > > - pos_out + *len < i_size_read(inode_out)) > > > > > > > + if (pos_out + *len < i_size_read(inode_out)) > > > > > > > new_len &= ~blkmask; > > > > > > > > > > > > > > if (new_len == *len) > > > > > > > -- > > > > > > > 2.11.0 > > > > > > >