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ext4: avoid uneeded calls to ext4_mb_load_buddy() while reading mb_groups

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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>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Aditya Kali 2012-06-30 19:10:57 -04:00 committed by Theodore Ts'o
parent 6887a4131d
commit 1c8457cadc
1 changed files with 15 additions and 8 deletions
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23
fs/ext4/mballoc.c
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@ -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];
@ -2095,15 +2096,21 @@ 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);