From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0F7AA3876C3 for ; Fri, 14 Aug 2026 23:57:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786751871; cv=none; b=TFlJpetAuyyKmkemoQ4KqD7hXqpsWSgReCOSPV5bxPDfJTcynZ/jAqYOL9v0HhnvTI8w6fDT2acwLPDO3iphSlh8wAQCMDnXv6Wmy1K7GtUvtjHKxO6Nuqkfq6DqI1/+Pf7nPgh1h4NBmMtHGOXnn2H/VxHkMQqgCLVcCYh9Vy0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786751871; c=relaxed/simple; bh=YBPzphVfMkdDGwg+LQlXCCDYbiFBcSrrrA0KMeSrbUY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lTlaQP3vtapxUDnEhVHOpF6mH+6SCE6v25lycqGI1r3iCJOBRo7HrbxSCwPxms7QzzaHqYufinPusmeAtQDwAaJYUXdBf+XM6tkTfqA4Ns20g9N7AoXhoAUKMalWYK3rbUnw09SKLVlYtYRKxjkg1qTLPAncdSwNquua8bxpc9w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=okUOpX6T; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="okUOpX6T" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 748F51F000E9; Fri, 14 Aug 2026 23:57:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786751869; bh=E40ZYS0CNG7+plkUMGHEuMKFBUe7hxR4KdHrT7fvO6Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=okUOpX6Tl5ksLdh9gX1gsARN/4H2yjV3lh1Z5MrtqrGlBnT7xI2k98iKs2eD8NaL0 UzNeqElDdIjKtWgh7AsNx3UYOv1ziIIrbFSq7GBoxnuud0f0BSbT8GxsSfw6+2st/4 n+coAsv0AIuMi0AmQahct8vpQRx82sNkpve1mG1VEyL4dwtNb/yDXM/r2X99EGqXtT aepjGu1j70z9tYptFWHWERdaM4foFdub64M3nPHe9JlOVNcPX4dI8tEiAion46LR/f EGQDIk0gzNPukwFuXTfT3aWU5xOi5qYX5D8fuD7ARn5br38YM/DwGzJvp33nIjZYQ1 SIY+suHeNKlgg== Date: Fri, 14 Aug 2026 16:57:48 -0700 From: "Darrick J. Wong" To: Brian Foster Cc: linux-xfs@vger.kernel.org, Matt Fleming Subject: Re: [PATCH v2 3/3] xfs: incorporate increased AGFL min requirement for minleft allocs Message-ID: <20260814235748.GL3556460@frogsfrogsfrogs> References: <20260814132239.271492-1-bfoster@redhat.com> <20260814132239.271492-4-bfoster@redhat.com> 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: <20260814132239.271492-4-bfoster@redhat.com> On Fri, Aug 14, 2026 at 09:22:39AM -0400, Brian Foster wrote: > Matt Fleming reports a filesystem shutdown due to inobt block > allocation failure during sparse chunk allocation. Inode creation > can involve multiple allocations in a transaction: the initial chunk > allocation and inode btree blocks via inobt record insertion. This > is expected to be safe by using the minleft parameter on the chunk > allocation to guarantee the selected AG has blocks available for > a followup inobt insertion. > > The sequence that leads to this failure is that the alloc and inode > btrees are all full (require a full split on next insertion) and the > AG has just enough free space to satisfy a sparse chunk allocation > with minleft set (i.e. 7 blocks in this example). The chunk > allocation splits a free extent, triggers full allocbt splits, and > consumes 4 free blocks for the chunk and 4 AGFL blocks for the > btrees. > > Next, the inobt record insertion triggers an inobt split. The AG has > enough free blocks, but the allocbt splits caused by the chunk > allocation have increased the min AGFL requirement for the AG due to > btree level increases. The AGFL requirement as calculated by > xfs_alloc_fix_freelist() is: > > free + AGFL - res - minfree - minleft = avail > > This evaluates to the following on initial chunk allocation: > > 2514 + 8 - 2505 - 8 - 2 = 7 > > ... and then after the chunk allocation but before the inobt block > allocation: > > 2510 + 4 - 2505 - 12 - 0 = -3 > > This causes the inobt alloc to fail despite minleft being set in the > first allocation. The error path cancels the dirty transaction and > shuts down the fs. > > The problem here is that while minleft ensures free blocks are > available for the inobt insert, it is not sufficient to cover the > increase of the AGFL min free requirement. To address this, create a > variant of the AGFL min free calculation for minleft allocations > that incorporates an additional allocbt level increase. > > We do not add the additional blocks directly to min_free because > this would lead to spurious AGFL block allocations and frees in the > common case (i.e. no btree splits). Instead, add the surplus block > requirement to the minleft value used to select the AG. This ensures > the AG has enough blocks for the caller's minleft value plus the > worst case increase in the AGFL. In the example above, the initial > calculation now evaluates to 3 blocks available instead of 7 and the > sparse inode allocation fails gracefully with -ENOSPC. Hrmm. So if I'm understanding this correctly, you're adding to minleft (if one has been set) enough space to handle an AGFL expansion resulting from the free space / rmap btrees expanding in height? And you're effectively saying that we'd rather fail creation and writes with ENOSPC a little earlier to handle that, than risk a shutdown? --D > Reported-by: Matt Fleming > Assisted-by: LLM > Signed-off-by: Brian Foster > --- > fs/xfs/libxfs/xfs_alloc.c | 29 ++++++++++++++++++++++++++++- > fs/xfs/libxfs/xfs_alloc.h | 2 ++ > fs/xfs/libxfs/xfs_bmap.c | 2 +- > 3 files changed, 31 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c > index dbb85fb6314b..74c5b587c87b 100644 > --- a/fs/xfs/libxfs/xfs_alloc.c > +++ b/fs/xfs/libxfs/xfs_alloc.c > @@ -2500,6 +2500,20 @@ xfs_alloc_min_freelist( > return __xfs_alloc_min_freelist(mp, pag, 0); > } > > +/* > + * Return the minimum freelist requirement considering a potential allocbt split > + * from the current allocation. Use this when computing longest free extent for > + * allocations with minleft set to ensure that the available extent length > + * accounts for the subsequent allocation's increased AGFL requirement. > + */ > +unsigned int > +xfs_alloc_min_freelist_minleft( > + struct xfs_mount *mp, > + struct xfs_perag *pag) > +{ > + return __xfs_alloc_min_freelist(mp, pag, 1); > +} > + > /* > * Check if the operation we are fixing up the freelist for should go ahead or > * not. If we are freeing blocks, we always allow it, otherwise the allocation > @@ -2517,6 +2531,7 @@ xfs_alloc_space_available( > xfs_extlen_t reservation; /* blocks that are still reserved */ > int available; > xfs_extlen_t agflcount; > + xfs_extlen_t minleft; > > if (flags & XFS_ALLOC_FLAG_FREEING) > return true; > @@ -2533,10 +2548,22 @@ xfs_alloc_space_available( > * Do we have enough free space remaining for the allocation? Don't > * account extra agfl blocks because we are about to defer free them, > * making them unavailable until the current transaction commits. > + * > + * If minleft is set, this allocation might cause an allocbt split that > + * increases the AGFL minimum for the next allocation in the > + * transaction. Reserve that space from the available block count > + * (without prematurely growing the AGFL) to prevent the subsequent > + * allocation from failing due to an increased min_free requirement. > */ > + minleft = args->minleft; > + if (minleft) { > + minleft += xfs_alloc_min_freelist_minleft(args->mp, pag) - > + min_free; > + } > + > agflcount = min_t(xfs_extlen_t, pag->pagf_flcount, min_free); > available = (int)(pag->pagf_freeblks + agflcount - > - reservation - min_free - args->minleft); > + reservation - min_free - minleft); > if (available < (int)max(args->total, alloc_len)) > return false; > > diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h > index 50ef79a1ed41..026b61a63994 100644 > --- a/fs/xfs/libxfs/xfs_alloc.h > +++ b/fs/xfs/libxfs/xfs_alloc.h > @@ -73,6 +73,8 @@ xfs_extlen_t xfs_alloc_longest_free_extent(struct xfs_perag *pag, > xfs_extlen_t need, xfs_extlen_t reserved); > unsigned int xfs_alloc_min_freelist(struct xfs_mount *mp, > struct xfs_perag *pag); > +unsigned int xfs_alloc_min_freelist_minleft(struct xfs_mount *mp, > + struct xfs_perag *pag); > int xfs_alloc_get_freelist(struct xfs_perag *pag, struct xfs_trans *tp, > struct xfs_buf *agfbp, xfs_agblock_t *bnop, int btreeblk); > int xfs_alloc_put_freelist(struct xfs_perag *pag, struct xfs_trans *tp, > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c > index d64defeda645..f396df864cf4 100644 > --- a/fs/xfs/libxfs/xfs_bmap.c > +++ b/fs/xfs/libxfs/xfs_bmap.c > @@ -3160,7 +3160,7 @@ xfs_bmap_longest_free_extent( > } > > longest = xfs_alloc_longest_free_extent(pag, > - xfs_alloc_min_freelist(pag_mount(pag), pag), > + xfs_alloc_min_freelist_minleft(pag_mount(pag), pag), > xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE)); > if (*blen < longest) > *blen = longest; > -- > 2.55.0 > >