Patch "xfs: prevent quotacheck from overloading inode lru" has been added to the 4.9-stable tree

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

xfs: prevent quotacheck from overloading inode lru

to the 4.9-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-prevent-quotacheck-from-overloading-inode-lru.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Brian Foster <[email protected]>
Date: Thu, 26 Jan 2017 13:18:09 -0800
Subject: xfs: prevent quotacheck from overloading inode lru

From: Brian Foster <[email protected]>

commit e0d76fa4475ef2cf4b52d18588b8ce95153d021b upstream.

Quotacheck runs at mount time in situations where quota accounting must be recalculated. In doing so, it uses bulkstat to visit every inode in the filesystem. Historically, every inode processed during quotacheck was released and immediately tagged for reclaim because quotacheck runs before the superblock is marked active by the VFS. In other words, the final iput() lead to an immediate ->destroy_inode() call, which allowed the XFS background reclaim worker to start reclaiming inodes.

Commit 17c12bcd3 ("xfs: when replaying bmap operations, don't let unlinked inodes get reaped") marks the XFS superblock active sooner as part of the mount process to support caching inodes processed during log recovery. This occurs before quotacheck and thus means all inodes processed by quotacheck are inserted to the LRU on release. The s_umount lock is held until the mount has completed and thus prevents the shrinkers from operating on the sb. This means that quotacheck can excessively populate the inode LRU and lead to OOM conditions on systems without sufficient RAM.

Update the quotacheck bulkstat handler to set XFS_IGET_DONTCACHE on inodes processed by quotacheck. This causes ->drop_inode() to return 1 and in turn causes iput_final() to evict the inode. This preserves the original quotacheck behavior and prevents it from overloading the LRU and running out of memory.

---
 fs/xfs/xfs_qm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -1177,7 +1177,8 @@ xfs_qm_dqusage_adjust(
 	 * the case in all other instances. It's OK that we do this because
 	 * quotacheck is done only at mount time.
 	 */
-	error = xfs_iget(mp, NULL, ino, 0, XFS_ILOCK_EXCL, &ip);
+	error = xfs_iget(mp, NULL, ino, XFS_IGET_DONTCACHE, XFS_ILOCK_EXCL,
+			 &ip);
 	if (error) {
 		*res = BULKSTAT_RV_NOTHING;
 		return error;

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

queue-4.9/xfs-prevent-quotacheck-from-overloading-inode-lru.patch