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Commit 1c8457ca authored by Aditya Kali's avatar Aditya Kali Committed by Theodore Ts'o
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ext4: avoid uneeded calls to ext4_mb_load_buddy() while reading mb_groups 



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: default avatarAditya Kali <adityakali@google.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 6887a413

fs/ext4/mballoc.c

+15 −8
Original line number Diff line number Diff line
@@ -2077,8 +2077,9 @@ 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];
@@ -2095,14 +2096,20 @@ 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);

	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;

		}

	ext4_lock_group(sb, group);

		buddy_loaded = 1;

	}



	memcpy(&sg, ext4_get_group_info(sb, group), i);

	ext4_unlock_group(sb, group);



	if (buddy_loaded)

		ext4_mb_unload_buddy(&e4b);



	seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,