[PATCH 8/8] inode: don't softlockup when evicting inodes

[Josef Bacik <jbacik@fb.com>]

On a box with a lot of ram (148gb) I can make the box softlockup after running
an fs_mark job that creates hundreds of millions of empty files.  This is
because we never generate enough memory pressure to keep the number of inodes on
our unused list low, so when we go to unmount we have to evict ~100 million
inodes.  This makes one processor a very unhappy person, so add a cond_resched()
in dispose_list() and cond_resched_lock() in the eviction isolation function to
combat this.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
---
 fs/inode.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index b961e5a..c58dbd3 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -574,6 +574,7 @@ static void dispose_list(struct list_head *head)
 		list_del_init(&inode->i_lru);
 
 		evict(inode);
+		cond_resched();
 	}
 }
 
@@ -592,6 +593,7 @@ void evict_inodes(struct super_block *sb)
 	LIST_HEAD(dispose);
 
 	spin_lock(&sb->s_inode_list_lock);
+again:
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
 		if (atomic_read(&inode->i_count))
 			continue;
@@ -606,6 +608,14 @@ void evict_inodes(struct super_block *sb)
 		inode_lru_list_del(inode);
 		spin_unlock(&inode->i_lock);
 		list_add(&inode->i_lru, &dispose);
+
+		/*
+		 * We can have a ton of inodes to evict at unmount time given
+		 * enough memory, check to see if we need to go to sleep for a
+		 * bit so we don't livelock.
+		 */
+		if (cond_resched_lock(&sb->s_inode_list_lock))
+			goto again;
 	}
 	spin_unlock(&sb->s_inode_list_lock);
 
-- 
1.8.3.1