Re: [PATCH] Set the initial TRIM information as TRIMMED

Eric Sandeen
2011-12-01T22:07:09Z

On 12/1/11 1:00 AM, Kyungmin Park wrote:
> From: Kyungmin Park <kyungmin.park@samsung.com>
>
> Now trim information doesn't stored at disk so every boot time. it's cleared.
> and do the trim all disk groups.
> But assume that it's already trimmed at previous time so don't need to trim it again. So set the intial state as trimmed.
>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index e2d8be8..97ef342 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -1098,6 +1098,12 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
> goto err;
> }
> mark_page_accessed(page);
> +
> + /*
> + * TRIM information is not stored at disk so set the initial
> + * state as trimmed. Since previous time it's already trimmed all
> + */
> + EXT4_MB_GRP_SET_TRIMMED(this_grp);

Hm, so if there were freed but un-trimmed blocks at this point, we will
never trim them until we free _another_ block in the group, right? That
might be a reasonable tradeoff, but it is somewhat surprising behavior.

i.e. say we do:

mount /mnt
rm -rf /mnt/very_big_file
umount /mnt

mount /mnt
fitrim /mnt

then we won't trim anything at all, right, despite there being many
new free blocks? Which would be rather unexpected.

If we don't store the trimmed state on disk, I think we should
probably stick with the slower first-time trim, and the more obvious
behavior (all free blocks are always trimmed whenever a trim
command is issued).

-Eric

> err:
> ext4_mb_put_buddy_page_lock(&e4b);
> return ret;
> --
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