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 A72BF18B49C; Fri, 23 Aug 2024 16:28:20 +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=1724430500; cv=none; b=WwCFZBzaNu0/l/ypwWGgSAXmSKEJAKoTc6CkFwtnHbcaj8ign28AVPLksnKvQ1uOkr+J+VxaxOdKRSGQ24qHMiEkpGizIdZZ6s1zswvvSzt6TTV5g87xnFxyGhW0QIowgLmlt4HEKeqvpBHkxjPVxjGo9spcn8BGQurLrVdALME= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724430500; c=relaxed/simple; bh=Fu4zYUmJgBcqoo3fJtRKVrGuO9BhONx3Z/G49nzToQw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jch7MadAFDVXzrxc8nMmT+/gfWqgIbQW6ljVGaToQHKDRXJDHP9nVrQiPz+w791tCOB50P5RiJO6mz21epoOk6FTJUFd+UVLRHzV9Ite6Oqz4j/RfOp88b1t87OhqFf4dmk9b//LRZJ17Lk8UpQke3U7ODm/1dRKEbTuqXYGnAE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IBd8AxYB; 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="IBd8AxYB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32BD0C32786; Fri, 23 Aug 2024 16:28:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724430500; bh=Fu4zYUmJgBcqoo3fJtRKVrGuO9BhONx3Z/G49nzToQw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IBd8AxYBTKrCLUyAyhzpDS8FlukESEFJTv3f2YOWiHpXBcemeHdns75+kq2Dvrf1p To1HylzD2NqADKx3FRArV6/1ATAA7RwZuIiMAE1daOD9tKwpQZIlc7wCu4cMjz7pz1 wyP85hqqo43AqocmM08Gx96/j1czPwXTdvtbxA33H4Kcd+RwN41hRQS5fEu+M/PZd/ RBjoJH0lc8Y7GnKbZRkoMlXq+TEWncf8NCuBu6olOs26i8b0bIlcVeAnJyZe3vhSOm B2eZncOpwzMqld7IyoOz1VoWFZWTO0ujW99CwU/1Di+hFECPH4g2VPuDQmPDYlXD6c H/2VglONz3cgw== Date: Fri, 23 Aug 2024 09:28:19 -0700 From: "Darrick J. Wong" To: John Garry Cc: chandan.babu@oracle.com, dchinner@redhat.com, hch@lst.de, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, catherine.hoang@oracle.com, martin.petersen@oracle.com Subject: Re: [PATCH v4 01/14] xfs: only allow minlen allocations when near ENOSPC Message-ID: <20240823162819.GB865349@frogsfrogsfrogs> References: <20240813163638.3751939-1-john.g.garry@oracle.com> <20240813163638.3751939-2-john.g.garry@oracle.com> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <20240813163638.3751939-2-john.g.garry@oracle.com> On Tue, Aug 13, 2024 at 04:36:25PM +0000, John Garry wrote: > From: Dave Chinner > > When we are near ENOSPC and don't have enough free > space for an args->maxlen allocation, xfs_alloc_space_available() > will trim args->maxlen to equal the available space. However, this > function has only checked that there is enough contiguous free space > for an aligned args->minlen allocation to succeed. Hence there is no > guarantee that an args->maxlen allocation will succeed, nor that the > available space will allow for correct alignment of an args->maxlen > allocation. > > Further, by trimming args->maxlen arbitrarily, it breaks an > assumption made in xfs_alloc_fix_len() that if the caller wants > aligned allocation, then args->maxlen will be set to an aligned > value. It then skips the tail alignment and so we end up with > extents that aren't aligned to extent size hint boundaries as we > approach ENOSPC. > > To avoid this problem, don't reduce args->maxlen by some random, > arbitrary amount. If args->maxlen is too large for the available > space, reduce the allocation to a minlen allocation as we know we > have contiguous free space available for this to succeed and always > be correctly aligned. > > Signed-off-by: Dave Chinner > Signed-off-by: John Garry Looks ok. I still have some misgivings about going straight to minlen, but that's a common tactic elsewhere in the allocator and at worst the performance is suboptimal. Reviewed-by: Darrick J. Wong --D > --- > fs/xfs/libxfs/xfs_alloc.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c > index 59326f84f6a5..d559d992c6ef 100644 > --- a/fs/xfs/libxfs/xfs_alloc.c > +++ b/fs/xfs/libxfs/xfs_alloc.c > @@ -2524,14 +2524,23 @@ xfs_alloc_space_available( > if (available < (int)max(args->total, alloc_len)) > return false; > > + if (flags & XFS_ALLOC_FLAG_CHECK) > + return true; > + > /* > - * Clamp maxlen to the amount of free space available for the actual > - * extent allocation. > + * If we can't do a maxlen allocation, then we must reduce the size of > + * the allocation to match the available free space. We know how big > + * the largest contiguous free space we can allocate is, so that's our > + * upper bound. However, we don't exaclty know what alignment/size > + * constraints have been placed on the allocation, so we can't > + * arbitrarily select some new max size. Hence make this a minlen > + * allocation as we know that will definitely succeed and match the > + * callers alignment constraints. > */ > - if (available < (int)args->maxlen && !(flags & XFS_ALLOC_FLAG_CHECK)) { > - args->maxlen = available; > + alloc_len = args->maxlen + (args->alignment - 1) + args->minalignslop; > + if (longest < alloc_len) { > + args->maxlen = args->minlen; > ASSERT(args->maxlen > 0); > - ASSERT(args->maxlen >= args->minlen); > } > > return true; > -- > 2.31.1 > >