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From:   Wen Yang <wenyang@linux.alibaba.com>
To:     tytso@mit.edu, Andreas Dilger <adilger.kernel@dilger.ca>
Cc:     Wen Yang <wenyang@linux.alibaba.com>,
        Baoyou Xie <baoyou.xie@alibaba-inc.com>,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] fs/ext4: remove redundant initialization of variable busy
Date:   Wed, 21 Apr 2021 23:54:55 +0800
Message-Id: <20210421155455.51725-1-wenyang@linux.alibaba.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The variable status is being initialized with a value that is never
read and it is being updated later with a new value. The initialization
is redundant and could be removed. Also put the variable declarations
into reverse christmas tree order. Finally, we add the log printing and
ext4_mb_show_pa() for troubleshooting, they are enabled only when
CONFIG_EXT4_DEBUG is set.

Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Baoyou Xie <baoyou.xie@alibaba-inc.com>
Cc: linux-ext4@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 fs/ext4/mballoc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a02fadf..1402b14 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -351,6 +351,8 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
 						ext4_group_t group);
 static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
 
+static inline void ext4_mb_show_pa(struct super_block *sb);
+
 /*
  * The algorithm using this percpu seq counter goes below:
  * 1. We sample the percpu discard_pa_seq counter before trying for block
@@ -4217,9 +4219,9 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
 	struct ext4_prealloc_space *pa, *tmp;
 	struct list_head list;
 	struct ext4_buddy e4b;
+	int free_total = 0;
+	int busy, free;
 	int err;
-	int busy = 0;
-	int free, free_total = 0;
 
 	mb_debug(sb, "discard preallocation for group %u\n", group);
 	if (list_empty(&grp->bb_prealloc_list))
@@ -4247,6 +4249,7 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
 
 	INIT_LIST_HEAD(&list);
 repeat:
+	busy = 0;
 	free = 0;
 	ext4_lock_group(sb, group);
 	list_for_each_entry_safe(pa, tmp,
@@ -4255,6 +4258,8 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
 		if (atomic_read(&pa->pa_count)) {
 			spin_unlock(&pa->pa_lock);
 			busy = 1;
+			mb_debug(sb, "used pa while discarding for group %u\n", group);
+			ext4_mb_show_pa(sb);
 			continue;
 		}
 		if (pa->pa_deleted) {
@@ -4300,7 +4305,6 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
 	if (free_total < needed && busy) {
 		ext4_unlock_group(sb, group);
 		cond_resched();
-		busy = 0;
 		goto repeat;
 	}
 	ext4_unlock_group(sb, group);
-- 
1.8.3.1