On Tue, 30 Mar 2010 20:36:17 +0800, jing zhang <zj.barak@xxxxxxxxx> wrote:
> From: Jing Zhang <zj.barak@xxxxxxxxx>
>
> Date: Tue Mar 30 20:35:22 2010
>
> With the added cache, better group locality may be earned when
> allocating blocks.
>
> Cc: Theodore Ts'o <tytso@xxxxxxx>
> Cc: Andreas Dilger <adilger@xxxxxxx>
> Cc: Dave Kleikamp <shaggy@xxxxxxxxxxxxxxxxxx>
> Cc: "Aneesh Kumar K. V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jing Zhang <zj.barak@xxxxxxxxx>
>
> ---
>
> --- linux-2.6.32/fs/ext4/mballoc.c 2009-12-03 11:51:22.000000000 +0800
> +++ ext4_mm_leak/mballoc-13.c 2010-03-30 20:28:08.000000000 +0800
> @@ -4183,12 +4183,20 @@ static int ext4_mb_discard_preallocation
> ext4_group_t i, ngroups = ext4_get_groups_count(sb);
> int ret;
> int freed = 0;
> + static ext4_group_t grp_cache = 0;
>
> trace_ext4_mb_discard_preallocations(sb, needed);
> - for (i = 0; i < ngroups && needed > 0; i++) {
> - ret = ext4_mb_discard_group_preallocations(sb, i, needed);
> + if (needed <= 0)
> + return freed;
> + for (i = 0; i < ngroups; i++) {
> + if (grp_cache >= ngroups)
> + grp_cache -= ngroups;
> + ret = ext4_mb_discard_group_preallocations(sb, grp_cache, needed);
> freed += ret;
> needed -= ret;
> + if (needed <= 0)
> + break;
> + grp_cache++;
> }
>
> return freed;
can you explain this further ?
-aneesh
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