[PATCH] ext4: replace open coded nofail allocation

[PATCH] ext4: replace open coded nofail allocation

[Michal Hocko]

ext4_free_blocks is looping around the allocation request and mimics
__GFP_NOFAIL behavior without any allocation fallback strategy. Let's
remove the open coded loop and replace it with __GFP_NOFAIL. Without
the flag the allocator has no way to find out never-fail requirement
and cannot help in any way.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---

Hi Ted,
I am sorry for seding these changes one at the time but I haven't found
a proper way to find all of them automatically. So I am discovering
them as I check the code due to other reasons.

Thanks!

 fs/ext4/mballoc.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8d1e60214ef0..41260489d3bc 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4800,18 +4800,12 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 		/*
 		 * blocks being freed are metadata. these blocks shouldn't
 		 * be used until this transaction is committed
+		 *
+		 * We use __GFP_NOFAIL because ext4_free_blocks() is not allowed
+		 * to fail.
 		 */
-	retry:
-		new_entry = kmem_cache_alloc(ext4_free_data_cachep, GFP_NOFS);
-		if (!new_entry) {
-			/*
-			 * We use a retry loop because
-			 * ext4_free_blocks() is not allowed to fail.
-			 */
-			cond_resched();
-			congestion_wait(BLK_RW_ASYNC, HZ/50);
-			goto retry;
-		}
+		new_entry = kmem_cache_alloc(ext4_free_data_cachep,
+				GFP_NOFS|__GFP_NOFAIL);
 		new_entry->efd_start_cluster = bit;
 		new_entry->efd_group = block_group;
 		new_entry->efd_count = count_clusters;
-- 
2.1.4

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Re: [PATCH] ext4: replace open coded nofail allocation

[Theodore Ts'o]

On Tue, Jun 23, 2015 at 11:50:37AM +0200, Michal Hocko wrote:
> ext4_free_blocks is looping around the allocation request and mimics
> __GFP_NOFAIL behavior without any allocation fallback strategy. Let's
> remove the open coded loop and replace it with __GFP_NOFAIL. Without
> the flag the allocator has no way to find out never-fail requirement
> and cannot help in any way.
> 
> Signed-off-by: Michal Hocko <mhocko@suse.cz>

Thanks, applied.

					- Ted

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