From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 DD9982236F7; Thu, 6 Feb 2025 21:50:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738878616; cv=none; b=rvWfPzunZLbUyCaJm1axp5Chkl1gNtFIYJCb0xy7tiA2BNL/Vbp1fMJblhSUepX20afFDYNXqkYqxCBY/l5UXcspMGH65UrNBm2Kb/9w5pF2FY7i2gdqPhQMbVcrzTIOC26vkXm7qLjKvapjEoy/bZbRFEr6+GTG3f7WdLu3hcY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738878616; c=relaxed/simple; bh=Ubxei8U3JTtyPTNq58vGjWgHxVoG/GGbarYbPV1Eqqw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=d/iu1UTnC5g/RSoV3I0oj0Wqs0H31Eylao7JUDSocD9vDEHqVYmyE2A8VzzzsHB/fbXu7GhZf4gCEAyot60S1usf+/vVji59c4Y8SzMSB97+h1dTZQaysTITHR8YzOZxTaswRY+/wzIf/b3QVecyBOTFGBWm27VHp33DWYb/30A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LLjXNQud; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LLjXNQud" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4274FC4CEDD; Thu, 6 Feb 2025 21:50:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738878615; bh=Ubxei8U3JTtyPTNq58vGjWgHxVoG/GGbarYbPV1Eqqw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LLjXNQudWmRjzfBSwc4V2vNciIDjiWTgym/xxrkSUx0PajM4zQfwNO3sPCj2e3kPv mbPlZA3sYP4zhYB4fPgF4ilwbXAJ+31UiUX+R9GJxPa3erQ0niWdbag42TrrdtBozI fbEXaO8qOOPelaJT1I2By94VKWmKnI/uS4WTlm/OGco7dJrk5T69cNXj3C6lev7oFR M/8rc2SDu9GwzqmCPR0fM6H0skenlwxYJmZ4rASwmiCJ8xl/8VxsTjGJB2YM104rkr m9jUz96wviU8qFJGQm2ioKub6QoJ2SIUftJYbATiJnWkxouJTus1AY+XY3ssZjjYmB Hzm5EczVw5kCA== Date: Thu, 6 Feb 2025 13:50:14 -0800 From: "Darrick J. Wong" To: John Garry Cc: brauner@kernel.org, cem@kernel.org, dchinner@redhat.com, hch@lst.de, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ojaswin@linux.ibm.com, ritesh.list@gmail.com, martin.petersen@oracle.com Subject: Re: [PATCH RFC 08/10] xfs: Commit CoW-based atomic writes atomically Message-ID: <20250206215014.GX21808@frogsfrogsfrogs> References: <20250204120127.2396727-1-john.g.garry@oracle.com> <20250204120127.2396727-9-john.g.garry@oracle.com> <20250205194740.GW21808@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Feb 06, 2025 at 10:27:45AM +0000, John Garry wrote: > On 05/02/2025 19:47, Darrick J. Wong wrote: > > On Tue, Feb 04, 2025 at 12:01:25PM +0000, John Garry wrote: > > > When completing a CoW-based write, each extent range mapping update is > > > covered by a separate transaction. > > > > > > For a CoW-based atomic write, all mappings must be changed at once, so > > > change to use a single transaction. > > > > > > Signed-off-by: John Garry > > > --- > > > fs/xfs/xfs_file.c | 5 ++++- > > > fs/xfs/xfs_reflink.c | 48 ++++++++++++++++++++++++++++++++++++++++++++ > > > fs/xfs/xfs_reflink.h | 3 +++ > > > 3 files changed, 55 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > > index 12af5cdc3094..170d7891f90d 100644 > > > --- a/fs/xfs/xfs_file.c > > > +++ b/fs/xfs/xfs_file.c > > > @@ -527,7 +527,10 @@ xfs_dio_write_end_io( > > > nofs_flag = memalloc_nofs_save(); > > > if (flags & IOMAP_DIO_COW) { > > > - error = xfs_reflink_end_cow(ip, offset, size); > > > + if (iocb->ki_flags & IOCB_ATOMIC) > > > + error = xfs_reflink_end_atomic_cow(ip, offset, size); > > > + else > > > + error = xfs_reflink_end_cow(ip, offset, size); > > > if (error) > > > goto out; > > > } > > > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > > > index dbce333b60eb..60c986300faa 100644 > > > --- a/fs/xfs/xfs_reflink.c > > > +++ b/fs/xfs/xfs_reflink.c > > > @@ -990,6 +990,54 @@ xfs_reflink_end_cow( > > > trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_); > > > return error; > > > } > > > +int > > > +xfs_reflink_end_atomic_cow( > > > + struct xfs_inode *ip, > > > + xfs_off_t offset, > > > + xfs_off_t count) > > > +{ > > > + xfs_fileoff_t offset_fsb; > > > + xfs_fileoff_t end_fsb; > > > + int error = 0; > > > + struct xfs_mount *mp = ip->i_mount; > > > + struct xfs_trans *tp; > > > + unsigned int resblks; > > > + bool commit = false; > > > + > > > + trace_xfs_reflink_end_cow(ip, offset, count); > > > + > > > + offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset); > > > + end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count); > > > + > > > + resblks = XFS_NEXTENTADD_SPACE_RES(ip->i_mount, > > > + (unsigned int)(end_fsb - offset_fsb), > > > + XFS_DATA_FORK); > > > + > > > + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, > > > > xfs gained reflink support for realtime volumes in 6.14-rc1, so you now > > have to calculate for that in here too. > > > > > + XFS_TRANS_RESERVE, &tp); > > > + if (error) > > > + return error; > > > + > > > + xfs_ilock(ip, XFS_ILOCK_EXCL); > > > + xfs_trans_ijoin(tp, ip, 0); > > > + > > > + while (end_fsb > offset_fsb && !error) > > > + error = xfs_reflink_end_cow_extent_locked(ip, &offset_fsb, > > > + end_fsb, tp, &commit); > > > > Hmm. Attaching intent items to a transaction consumes space in that > > transaction, so we probably ought to limit the amount that we try to do > > here. Do you know what that limit is? I don't, > > nor do I ... > > > but it's roughly > > tr_logres divided by the average size of a log intent item. > > So you have a ballpark figure on the average size of a log intent item, or > an idea on how to get it? You could add up the size of struct xfs_{bui,rmap,refcount,efi}_log_format structures and add 20%, that will give you a ballpark figure of the worst case per-block requirements. My guess is that 64 blocks is ok provided resblks is big enough. But I guess we could estimate it (very conservatively) dynamically too. (also note tr_itruncate declares more logres) > > This means we need to restrict the size of an untorn write to a > > double-digit number of fsblocks for safety. > > Sure, but won't we also still be liable to suffer the same issue which was > fixed in commit d6f215f359637? Yeah, come to think of it, you need to reserve the worst case space reservation, i.e. each of the blocks between offset_fsb and end_fsb becomes a separate btree update. resblks = (end_fsb - offset_fsb) * XFS_NEXTENTADD_SPACE_RES(mp, 1, XFS_DATA_FORK); --D > > > > The logic in here looks reasonable though. > > > > Thanks, > John > > > --D > > > > > + > > > + if (error || !commit) > > > + goto out_cancel; > > > + > > > + if (error) > > > + trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_); > > > + error = xfs_trans_commit(tp); > > > + xfs_iunlock(ip, XFS_ILOCK_EXCL); > > > + return error; > > > +out_cancel: > > > + xfs_trans_cancel(tp); > > > + xfs_iunlock(ip, XFS_ILOCK_EXCL); > > > + return error; > > > +} > > > /* > > > * Free all CoW staging blocks that are still referenced by the ondisk refcount > > > diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h > > > index ef5c8b2398d8..2c3b096c1386 100644 > > > --- a/fs/xfs/xfs_reflink.h > > > +++ b/fs/xfs/xfs_reflink.h > > > @@ -45,6 +45,9 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset, > > > xfs_off_t count, bool cancel_real); > > > extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset, > > > xfs_off_t count); > > > + int > > > +xfs_reflink_end_atomic_cow(struct xfs_inode *ip, xfs_off_t offset, > > > + xfs_off_t count); > > > extern int xfs_reflink_recover_cow(struct xfs_mount *mp); > > > extern loff_t xfs_reflink_remap_range(struct file *file_in, loff_t pos_in, > > > struct file *file_out, loff_t pos_out, loff_t len, > > > -- > > > 2.31.1 > > > > > > > >