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 AD64416A927; Fri, 21 Jun 2024 20:04:09 +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=1719000249; cv=none; b=WUk3xw7bJTZWb9IUy5cuTDnJAA9VfyZXUSZACtImzJKo6VKeb+eW9oGEj6FGfFlA/PWdN/EEyusMgX/zwyIRMUNlZ9ABP/BPNcJZH2UO0j0Zr/cakdSQ4OU7thGh0vw6sFqaY6p2OfWeN8RmQvSJOxOQ9LPUj4uRKgsog3BsgvE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719000249; c=relaxed/simple; bh=g1gIkh1N7dpwladx/+giHa5C+3qDTtIwQQCFFklKWwo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=THH/rYaAAxFbWYiuiebmCBOKaqbuOAl778QH00wucvoWl1MOgBm88fZYs/xi88QwaJ5XJkE4hRKhkweDT/UeBEuIQD0ryY0DWDT6RRSNBm5+k0IB+6ZB8FwP3Nzp/wwyX2czIShs6pJSQmygIxS/TrVRTn/eOKbe33HT/d+O9xY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OJ1sMRLZ; 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="OJ1sMRLZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 27B01C2BBFC; Fri, 21 Jun 2024 20:04:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719000249; bh=g1gIkh1N7dpwladx/+giHa5C+3qDTtIwQQCFFklKWwo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OJ1sMRLZ4WzWNLmbaZ3AcgUCaOKrV0yT4+JpzN9hMhj4m1eNv31fGmCGTzG7No0vo ef8aa/lU2ERbrgaIMqv/gNmBsOfLkJ7jlSCaV1FW0r7peC/xGAYRICYEOgnBgatmgo 5QIc1Y5PYD+MVbW7Zw8Ag0WoNEVU1lJfcGabPwRJDwRo2JaAbsNTne5O2mSLgNHqYM 5Uh3tejy9VUI/o8ifogC1yI2srTWsRGbyX8tD3dR09m7/XzRxwt1xL1zL3F6n3Psz9 CO+BnNIo+lx7e6VDcoYO2dpewL/xRawV6lFjo7Oyz+VnshxPZvGVNUptMtjoM+PZX8 HiYeRhcPV4UCw== Date: Fri, 21 Jun 2024 13:04:08 -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 01/13] xfs: only allow minlen allocations when near ENOSPC Message-ID: <20240621200408.GA103014@frogsfrogsfrogs> References: <20240621100540.2976618-1-john.g.garry@oracle.com> <20240621100540.2976618-2-john.g.garry@oracle.com> <20240621194225.GR3058325@frogsfrogsfrogs> 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: <20240621194225.GR3058325@frogsfrogsfrogs> On Fri, Jun 21, 2024 at 12:42:25PM -0700, Darrick J. Wong wrote: > On Fri, Jun 21, 2024 at 10:05:28AM +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 > > --- > > 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 6c55a6e88eba..5855a21d4864 100644 > > --- a/fs/xfs/libxfs/xfs_alloc.c > > +++ b/fs/xfs/libxfs/xfs_alloc.c > > @@ -2409,14 +2409,23 @@ 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; > > Didn't we already calculate alloc_len identically under "do we have > enough contiguous free space for the allocation?"? AFAICT we haven't > alter anything in @args since then, right? Oops, the first computation uses minlen, whereas this one uses maxlen. Disregard this question, please. --D > > + if (longest < alloc_len) { > > + args->maxlen = args->minlen; > > Is it possible to reduce maxlen the largest multiple of the alignment > that is still less than @longest? > > --D > > > ASSERT(args->maxlen > 0); > > - ASSERT(args->maxlen >= args->minlen); > > } > > > > return true; > > -- > > 2.31.1 > > > > >