[PATCH 1/4] ext4: use stream-alloc when mb_group_prealloc set to zero

[PATCH 1/4] ext4: use stream-alloc when mb_group_prealloc set to zero

[Robin Dong]

From: Robin Dong <sanbai@taobao.com>

The kernel will crash on 

ext4_mb_mark_diskspace_used:
	BUG_ON(ac->ac_b_ex.fe_len <= 0);

after we set /sys/fs/ext4/sda/mb_group_prealloc to zero and create new files in an ext4 filesystem.

The reason is: ac_b_ex.fe_len also set to zero(mb_group_prealloc) in ext4_mb_normalize_group_request
because the ac_flags contains EXT4_MB_HINT_GROUP_ALLOC.

I think when someone set mb_group_prealloc to zero, it means DO NOT USE GROUP PREALLOCATION,
so we should set alloc-strategy to STREAM in this case.

Signed-off-by: Robin Dong <sanbai@taobao.com>
---
 fs/ext4/mballoc.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 17a5a57..6b58247 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3969,6 +3969,11 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
 		return;
 	}
 
+	if (sbi->s_mb_group_prealloc <= 0) {
+		ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
+		return;
+	}
+
 	/* don't use group allocation for large files */
 	size = max(size, isize);
 	if (size > sbi->s_mb_stream_request) {
-- 
1.7.4.1

[PATCH 2/4] ext4: remove unused argument in ext4_mb_generate_from_pa

[Robin Dong]

From: Robin Dong <sanbai@taobao.com>

The argument 'count' in function ext4_mb_generate_from_pa looks useless,
so clean it.

Signed-off-by: Robin Dong <sanbai@taobao.com>
---
 fs/ext4/mballoc.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 6b58247..d0fc76e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3312,7 +3312,6 @@ void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
 	ext4_group_t groupnr;
 	ext4_grpblk_t start;
 	int preallocated = 0;
-	int count = 0;
 	int len;
 
 	/* all form of preallocation discards first load group,
@@ -3335,7 +3334,6 @@ void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
 		BUG_ON(groupnr != group);
 		ext4_set_bits(bitmap, start, len);
 		preallocated += len;
-		count++;
 	}
 	mb_debug(1, "prellocated %u for group %u\n", preallocated, group);
 }
-- 
1.7.4.1

[PATCH 3/4] ext4: remove unused argument in mb_find_extent

[Robin Dong]

From: Robin Dong <sanbai@taobao.com>

The argument 'ord' in function mb_find_extent is redundant,
so remove it.

Signed-off-by: Robin Dong <sanbai@taobao.com>
---
 fs/ext4/mballoc.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d0fc76e..99d123a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1390,7 +1390,6 @@ static int mb_find_extent(struct ext4_buddy *e4b, int order, int block,
 {
 	int next = block;
 	int max;
-	int ord;
 	void *buddy;
 
 	assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
@@ -1432,9 +1431,8 @@ static int mb_find_extent(struct ext4_buddy *e4b, int order, int block,
 		if (mb_test_bit(next, EXT4_MB_BITMAP(e4b)))
 			break;
 
-		ord = mb_find_order_for_block(e4b, next);
+		order = mb_find_order_for_block(e4b, next);
 
-		order = ord;
 		block = next >> order;
 		ex->fe_len += 1 << order;
 	}
-- 
1.7.4.1

[PATCH 4/4] ext4: fix a wrong comment in __mb_check_buddy

[Robin Dong]

From: Robin Dong <sanbai@taobao.com>

The comment says the bit should be 0, but the after code assert the bit to be 1.
This makes people confused, so fix it.

Signed-off-by: Robin Dong <sanbai@taobao.com>
---
 fs/ext4/mballoc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 99d123a..0b3d0ee 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -580,7 +580,7 @@ static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
 				continue;
 			}
 
-			/* both bits in buddy2 must be 0 */
+			/* both bits in buddy2 must be 1 */
 			MB_CHECK_ASSERT(mb_test_bit(i << 1, buddy2));
 			MB_CHECK_ASSERT(mb_test_bit((i << 1) + 1, buddy2));
 
-- 
1.7.4.1

Re: [PATCH 1/4] ext4: use stream-alloc when mb_group_prealloc set to zero

[Ted Ts'o]

On Thu, Sep 15, 2011 at 03:09:37PM +0800, Robin Dong wrote:
> From: Robin Dong <sanbai@taobao.com>
> 
> The kernel will crash on 
> 
> ext4_mb_mark_diskspace_used:
> 	BUG_ON(ac->ac_b_ex.fe_len <= 0);
> 
> after we set /sys/fs/ext4/sda/mb_group_prealloc to zero and create new files in an ext4 filesystem.
> 
> The reason is: ac_b_ex.fe_len also set to zero(mb_group_prealloc) in ext4_mb_normalize_group_request
> because the ac_flags contains EXT4_MB_HINT_GROUP_ALLOC.
> 
> I think when someone set mb_group_prealloc to zero, it means DO NOT USE GROUP PREALLOCATION,
> so we should set alloc-strategy to STREAM in this case.
> 
> Signed-off-by: Robin Dong <sanbai@taobao.com>

Thanks, applied.

						- Ted

Re: [PATCH 2/4] ext4: remove unused argument in ext4_mb_generate_from_pa

[Ted Ts'o]

On Thu, Sep 15, 2011 at 03:09:38PM +0800, Robin Dong wrote:
> From: Robin Dong <sanbai@taobao.com>
> 
> The argument 'count' in function ext4_mb_generate_from_pa looks useless,
> so clean it.
> 
> Signed-off-by: Robin Dong <sanbai@taobao.com>

Thanks, applied.

					- Ted

Re: [PATCH 3/4] ext4: remove unused argument in mb_find_extent

[Ted Ts'o]

On Thu, Sep 15, 2011 at 03:09:39PM +0800, Robin Dong wrote:
> From: Robin Dong <sanbai@taobao.com>
> 
> The argument 'ord' in function mb_find_extent is redundant,
> so remove it.
> 
> Signed-off-by: Robin Dong <sanbai@taobao.com>

Thanks, applied.

In both this and the previous patch, I changed "argument" to
"variable" for clarity/correctness in the git commit log.

	       			      	  - Ted

Re: [PATCH 4/4] ext4: fix a wrong comment in __mb_check_buddy

[Ted Ts'o]

On Thu, Sep 15, 2011 at 03:09:40PM +0800, Robin Dong wrote:
> From: Robin Dong <sanbai@taobao.com>
> 
> The comment says the bit should be 0, but the after code assert the bit to be 1.
> This makes people confused, so fix it.
> 
> Signed-off-by: Robin Dong <sanbai@taobao.com>

Thanks, applied.

						- Ted