ext4-use-percpu-data-for-lg_prealloc_list

   1 ext4: use percpu data structures for lg_prealloc_list
   2
   3 From: Eric Sandeen <sandeen@redhat.com>
   4
   5 lg_prealloc_list seems to cry out for a per-cpu data structure; on a large
   6 smp system I think this should be better.  I've lightly tested this change
   7 on a 4-cpu system.
   8
   9 Signed-off-by: Eric Sandeen <sandeen@redhat.com>
  10 Acked-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
  11 ---
  12
  13  mballoc.c |   13 +++++--------
  14  1 file changed, 5 insertions(+), 8 deletions(-)
  15
  16 Index: linux-2.6/fs/ext4/mballoc.c
  17 ===================================================================
  18 --- linux-2.6.orig/fs/ext4/mballoc.c    2008-08-04 15:30:30.000000000 -0500
  19 +++ linux-2.6/fs/ext4/mballoc.c 2008-08-13 13:48:33.224165751 -0500
  20 @@ -2540,17 +2540,16 @@ int ext4_mb_init(struct super_block *sb,
  21         sbi->s_mb_history_filter = EXT4_MB_HISTORY_DEFAULT;
  22         sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
  23
  24 -       i = sizeof(struct ext4_locality_group) * nr_cpu_ids;
  25 -       sbi->s_locality_groups = kmalloc(i, GFP_KERNEL);
  26 +       sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
  27         if (sbi->s_locality_groups == NULL) {
  28                 clear_opt(sbi->s_mount_opt, MBALLOC);
  29                 kfree(sbi->s_mb_offsets);
  30                 kfree(sbi->s_mb_maxs);
  31                 return -ENOMEM;
  32         }
  33 -       for (i = 0; i < nr_cpu_ids; i++) {
  34 +       for_each_possible_cpu(i) {
  35                 struct ext4_locality_group *lg;
  36 -               lg = &sbi->s_locality_groups[i];
  37 +               lg = per_cpu_ptr(sbi->s_locality_groups, i);
  38                 mutex_init(&lg->lg_mutex);
  39                 for (j = 0; j < PREALLOC_TB_SIZE; j++)
  40                         INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
  41 @@ -2647,8 +2646,7 @@ int ext4_mb_release(struct super_block *
  42                                 atomic_read(&sbi->s_mb_discarded));
  43         }
  44
  45 -       kfree(sbi->s_locality_groups);
  46 -
  47 +       free_percpu(sbi->s_locality_groups);
  48         ext4_mb_history_release(sb);
  49         ext4_mb_destroy_per_dev_proc(sb);
  50
  51 @@ -4055,8 +4053,7 @@ static void ext4_mb_group_or_file(struct
  52          * per cpu locality group is to reduce the contention between block
  53          * request from multiple CPUs.
  54          */
  55 -       ac->ac_lg = &sbi->s_locality_groups[get_cpu()];
  56 -       put_cpu();
  57 +       ac->ac_lg = per_cpu_ptr(sbi->s_locality_groups, raw_smp_processor_id());
  58
  59         /* we're going to use group allocation */
  60         ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;
  61