[PATCH v2 5/5] ext4: Defer inode reclaim if it has preallocations

[Jan Kara <jack@suse.cz>]

When we have to free preallocations during inode eviction, we need to
load block bitmaps and run transaction to modify them. This takes time
and also requires GFP_NOFAIL allocations. Mark inodes with preallocated
blocks as needing offloading of inode reclaim to a workqueue so that we
don't block reclaim for long and potentially deadlock MM subsystem.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/mballoc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 06171a11db12..4891f252105e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3115,6 +3115,13 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 	if (ac->ac_prefetch_nr)
 		ext4_mb_prefetch_fini(sb, ac->ac_prefetch_grp, ac->ac_prefetch_nr);
 
+	/*
+	 * Freeing preallocations requires loading bitmaps and running
+	 * transactions. Defer inode reclaim to a workqueue.
+	 */
+	if (!RB_EMPTY_ROOT(&EXT4_I(ac->ac_inode)->i_prealloc_node))
+		mark_inode_reclaim_deferred(ac->ac_inode);
+
 	return err;
 }
 
-- 
2.51.0