percpu_counter: new function percpu_counter_sum_and_set

Delayed allocation need to check free blocks at every write time.
percpu_counter_read_positive() is not quit accurate. delayed
allocation need a more accurate accounting, but using
percpu_counter_sum_positive() is frequently is quite expensive.

This patch added a new function to update center counter when sum
per-cpu counter, to increase the accurate rate for next
percpu_counter_read() and require less calling expensive
percpu_counter_sum().

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 25f63d8c1b3d..6369bacf0dcb 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -1621,7 +1621,7 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
 #ifdef CONFIG_SMP
         if (free_blocks - root_blocks < FBC_BATCH)
                 free_blocks =
-                        percpu_counter_sum_positive(&sbi->s_freeblocks_counter);
+                        percpu_counter_sum_and_set(&sbi->s_freeblocks_counter);
 #endif
         if (free_blocks - root_blocks < nblocks)
                 return free_blocks - root_blocks;