On Mon 31-08-15 17:46:24, Zhang Zhen wrote:
> In ext4_mb_discard_group_preallocations(), if free is always less than needed,
> and some PAs are always used in every loop, it will be endless loop.
>
> Here we pick a random value to limit the max number of loop.
Were you able to trigger this in practice or is it just a theoretical
concern?
My slight concern is that in theory we could prematurely declare ENOSPC
with this patch since ext4_mb_discard_preallocations() doesn't reliably
discard all the preallocations anymore. But probably that's acceptable.
But we should add a comment before ext4_mb_discard_group_preallocations()
saying that the functions needn't free all the preallocations.
Honza
>
> Signed-off-by: Zhang Zhen <zhenzhang.zhang@xxxxxxxxxx>
> ---
> fs/ext4/mballoc.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 34b610e..553fbde 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3836,6 +3836,7 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
> int err;
> int busy = 0;
> int free = 0;
> + int tried = 0;
>
> mb_debug(1, "discard preallocation for group %u\n", group);
>
> @@ -3886,9 +3887,11 @@ repeat:
> list_add(&pa->u.pa_tmp_list, &list);
> }
>
> - /* if we still need more blocks and some PAs were used, try again */
> - if (free < needed && busy) {
> + /* if we still need more blocks and some PAs were used, try again,
> + here 20 is a ramdon value. */
> + if (free < needed && busy && tried < 20) {
> busy = 0;
> + tried++;
> ext4_unlock_group(sb, group);
> cond_resched();
> goto repeat;
> --
> 1.9.1
>
>
> .
>
>
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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