[PATCH] use percpu data for lg_prealloc_list

[Eric Sandeen <sandeen@redhat.com>]

lg_prealloc_list seems to cry out for a per-cpu data structure; on a large
smp system I think this should be better.  I've lightly tested this change
on a 4-cpu system.  Comments welcome...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

ndex: linux-2.6/fs/ext4/mballoc.c
===================================================================
--- linux-2.6.orig/fs/ext4/mballoc.c	2008-08-04 15:30:30.000000000 -0500
+++ linux-2.6/fs/ext4/mballoc.c	2008-08-13 13:48:33.224165751 -0500
@@ -2540,17 +2540,16 @@ int ext4_mb_init(struct super_block *sb,
 	sbi->s_mb_history_filter = EXT4_MB_HISTORY_DEFAULT;
 	sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
 
-	i = sizeof(struct ext4_locality_group) * nr_cpu_ids;
-	sbi->s_locality_groups = kmalloc(i, GFP_KERNEL);
+	sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
 	if (sbi->s_locality_groups == NULL) {
 		clear_opt(sbi->s_mount_opt, MBALLOC);
 		kfree(sbi->s_mb_offsets);
 		kfree(sbi->s_mb_maxs);
 		return -ENOMEM;
 	}
-	for (i = 0; i < nr_cpu_ids; i++) {
+	for_each_possible_cpu(i) {
 		struct ext4_locality_group *lg;
-		lg = &sbi->s_locality_groups[i];
+		lg = per_cpu_ptr(sbi->s_locality_groups, i);
 		mutex_init(&lg->lg_mutex);
 		for (j = 0; j < PREALLOC_TB_SIZE; j++)
 			INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
@@ -2647,8 +2646,7 @@ int ext4_mb_release(struct super_block *
 				atomic_read(&sbi->s_mb_discarded));
 	}
 
-	kfree(sbi->s_locality_groups);