[PATCH] ext4: Avoid unnecessary calls to ext4_mb_load_buddy while reading mb_groups proc file

[PATCH] ext4: Avoid unnecessary calls to ext4_mb_load_buddy while reading mb_groups proc file

[Aditya Kali]

Currently ext4_mb_load_buddy is called for every group, irrespective
of whether the group info is already in memory, while reading
/proc/fs/ext4/<partition>/mb_groups proc file. For the purpose of
mb_groups proc file, it is unnecessary to load the file group info
from disk if it was loaded in past. These calls to ext4_mb_load_buddy
make reading the mb_groups proc file expensive.
Also, the locks around ext4_get_group_info are not required.
This patch modifies the code to call ext4_mb_load_buddy only if the
group info had never been loaded into memory in past. It also removes
the mb group locking around ext4_get_group_info call.

Signed-off-by: Aditya Kali <adityakali@google.com>
---
 fs/ext4/mballoc.c |   23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 851f49b..5738082 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2171,8 +2171,9 @@ static int ext4_mb_seq_groups_show(struct
seq_file *seq, void *v)
 	struct super_block *sb = seq->private;
 	ext4_group_t group = (ext4_group_t) ((unsigned long) v);
 	int i;
-	int err;
+	int err, buddy_loaded = 0;
 	struct ext4_buddy e4b;
+	struct ext4_group_info *grinfo;
 	struct sg {
 		struct ext4_group_info info;
 		ext4_grpblk_t counters[16];
@@ -2189,15 +2190,21 @@ static int ext4_mb_seq_groups_show(struct
seq_file *seq, void *v)

 	i = (sb->s_blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
 		sizeof(struct ext4_group_info);
-	err = ext4_mb_load_buddy(sb, group, &e4b);
-	if (err) {
-		seq_printf(seq, "#%-5u: I/O error\n", group);
-		return 0;
+	grinfo = ext4_get_group_info(sb, group);
+	/* Load the group info in memory only if not already loaded. */
+	if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
+		err = ext4_mb_load_buddy(sb, group, &e4b);
+		if (err) {
+			seq_printf(seq, "#%-5u: I/O error\n", group);
+			return 0;
+		}
+		buddy_loaded = 1;
 	}
-	ext4_lock_group(sb, group);
+
 	memcpy(&sg, ext4_get_group_info(sb, group), i);
-	ext4_unlock_group(sb, group);
-	ext4_mb_unload_buddy(&e4b);
+
+	if (buddy_loaded)
+		ext4_mb_unload_buddy(&e4b);

 	seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
 			sg.info.bb_fragments, sg.info.bb_first_free);
-- 
1.7.3.1

Re: [PATCH] ext4: Avoid unnecessary calls to ext4_mb_load_buddy while reading mb_groups proc file

[Ted Ts'o]

On Fri, Jan 14, 2011 at 02:05:15PM -0800, Aditya Kali wrote:
> Currently ext4_mb_load_buddy is called for every group, irrespective
> of whether the group info is already in memory, while reading
> /proc/fs/ext4/<partition>/mb_groups proc file. For the purpose of
> mb_groups proc file, it is unnecessary to load the file group info
> from disk if it was loaded in past. These calls to ext4_mb_load_buddy
> make reading the mb_groups proc file expensive.
> Also, the locks around ext4_get_group_info are not required.
> This patch modifies the code to call ext4_mb_load_buddy only if the
> group info had never been loaded into memory in past. It also removes
> the mb group locking around ext4_get_group_info call.
> 
> Signed-off-by: Aditya Kali <adityakali@google.com>

I realized that this had dropped through the cracks.  Sorry!

I've queued this for the next merge window.

     	    	     	      	    - Ted