Patch "xfs: perag initialization should only touch m_ag_max_usable for AG 0" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

xfs: perag initialization should only touch m_ag_max_usable for AG 0

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xfs-perag-initialization-should-only-touch-m_ag_max_usable-for-ag-0.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Darrick J. Wong" <[email protected]>
Date: Mon, 18 Sep 2017 09:42:09 -0700
Subject: xfs: perag initialization should only touch m_ag_max_usable for AG 0

From: Darrick J. Wong <[email protected]>

commit 9789dd9e1d939232e8ff4c50ef8e75aa6781b3fb upstream.

We call __xfs_ag_resv_init to make a per-AG reservation for each AG. This makes the reservation per-AG, not per-filesystem. Therefore, it is incorrect to adjust m_ag_max_usable for each AG. Adjust it only when we're reserving AG 0's blocks so that we only do it once per fs.

---
 fs/xfs/libxfs/xfs_ag_resv.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

@@ -156,7 +156,8 @@ __xfs_ag_resv_free(
 	trace_xfs_ag_resv_free(pag, type, 0);
 
 	resv = xfs_perag_resv(pag, type);
-	pag->pag_mount->m_ag_max_usable += resv->ar_asked;
+	if (pag->pag_agno == 0)
+		pag->pag_mount->m_ag_max_usable += resv->ar_asked;
 	/*
 	 * AGFL blocks are always considered "free", so whatever
 	 * was reserved at mount time must be given back at umount.

@@ -216,7 +217,14 @@ __xfs_ag_resv_init(
 		return error;
 	}
 
-	mp->m_ag_max_usable -= ask;
+	/*
+	 * Reduce the maximum per-AG allocation length by however much we're
+	 * trying to reserve for an AG.  Since this is a filesystem-wide
+	 * counter, we only make the adjustment for AG 0.  This assumes that
+	 * there aren't any AGs hungrier for per-AG reservation than AG 0.
+	 */
+	if (pag->pag_agno == 0)
+		mp->m_ag_max_usable -= ask;
 
 	resv = xfs_perag_resv(pag, type);
 	resv->ar_asked = ask;

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/xfs-don-t-unconditionally-clear-the-reflink-flag-on-zero-block-files.patch queue-4.13/xfs-move-two-more-rt-specific-functions-into-config_xfs_rt.patch queue-4.13/xfs-cancel-dirty-pages-on-invalidation.patch queue-4.13/xfs-reinit-btree-pointer-on-attr-tree-inactivation-walk.patch queue-4.13/xfs-report-zeroed-or-not-correctly-in-xfs_zero_range.patch queue-4.13/xfs-move-more-rt-specific-code-under-config_xfs_rt.patch queue-4.13/xfs-don-t-change-inode-mode-if-acl-update-fails.patch queue-4.13/xfs-handle-error-if-xfs_btree_get_bufs-fails.patch queue-4.13/iomap_dio_rw-allocate-aio-completion-queue-before-submitting-dio.patch queue-4.13/xfs-update-i_size-after-unwritten-conversion-in-dio-completion.patch queue-4.13/xfs-trim-writepage-mapping-to-within-eof.patch queue-4.13/xfs-handle-racy-aio-in-xfs_reflink_end_cow.patch queue-4.13/xfs-evict-cow-fork-extents-when-performing-finsert-fcollapse.patch queue-4.13/xfs-capture-state-of-the-right-inode-in-xfs_iflush_done.patch queue-4.13/fs-xfs-use-ps-printk-format-for-direct-addresses.patch queue-4.13/xfs-perag-initialization-should-only-touch-m_ag_max_usable-for-ag-0.patch queue-4.13/xfs-always-swap-the-cow-forks-when-swapping-extents.patch queue-4.13/xfs-don-t-log-uninitialised-fields-in-inode-structures.patch