linux-kernel - [PATCH 3.2 067/110] ext4: replace open coded nofail allocation in ext4_free

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Message-ID: <lsq.1439201551.39439454@decadent.org.uk>
Date:	Mon, 10 Aug 2015 12:12:31 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Michal Hocko" <mhocko@...e.cz>,
	"Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3.2 067/110] ext4: replace open coded nofail allocation in
 ext4_free_blocks()

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@...e.cz>

commit 7444a072c387a93ebee7066e8aee776954ab0e41 upstream.

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@...e.cz>
Signed-off-by: Theodore Ts'o <tytso@....edu>
[bwh: Backported to 3.2:
 - Adjust context
 - s/ext4_free_data_cachep/ext4_free_ext_cachep/]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/mballoc.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4720,18 +4720,12 @@ do_more:
 		/*
 		 * 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_ext_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_ext_cachep,
+				GFP_NOFS|__GFP_NOFAIL);
 		new_entry->start_cluster = bit;
 		new_entry->group  = block_group;
 		new_entry->count = count_clusters;

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