commit 85c8f176a6111ecde9c158109989dbd445a0e59a
Author: Andrew Perepechko <andrew.perepechko@seagate.com>
AuthorDate: Sun Apr 30 00:46:35 2017 -0400
Commit: Theodore Ts'o <tytso@mit.edu>
CommitDate: Sun Apr 30 00:46:35 2017 -0400
ext4: preload block group descriptors

With enabled meta_bg option block group descriptors
reading IO is not sequential and requires optimization.

Signed-off-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Index: fs/ext4/super.c
===================================================================
--- linux-stage/fs/ext4/super.c.orig
+++ linux-stage.orig/fs/ext4/super.c
@@ -3918,6 +3919,12 @@ static int ext4_fill_super(struct super_
 
 	bgl_lock_init(sbi->s_blockgroup_lock);
 
+	/* Pre-read the descriptors into the buffer cache */
+	for (i = 0; i < db_count; i++) {
+		block = descriptor_loc(sb, logical_sb_block, i);
+		sb_breadahead(sb, block);
+	}
+
 	for (i = 0; i < db_count; i++) {
 		block = descriptor_loc(sb, logical_sb_block, i);
 		sbi->s_group_desc[i] = sb_bread(sb, block);