On Tue, Nov 21, 2017 at 7:21 AM, Qu Wenruo <wqu@xxxxxxxx> wrote:
> [BUG]
> fstrim on some btrfs only trims the unallocated space, not trimming any
> space in existing block groups.
>
> [CAUSE]
> fstrim_range passed in by default fstrim will be:
>
> range->start = 0
> range->len = fs_size (which equals with super->total_bytes)
> range->min_len = 512
>
> However btrfs_trim_fs() following above parameter to search block groups
> to trim.
>
> While it's quite possible that all chunks start beyond
> super->total_bytes if the fs is balanced several times.
>
> In that case, btrfs will skip trimming block groups and only trim the
> unallocated space of each device.
>
> [FIX]
> For common full fs trimming range passed in, extent its len to (u64)-1
> so we will iterate all block groups.
>
> And for custom fs trimming range, due to the fact that the range will
> always be truncated by range [0, super->total_bytes), making custom fs
> trimming range useless.
>
> Just return -ENOTTY for custom fs trimming range.
>
> Reported-by: Chris Murphy <lists@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3a252d7af158..22bbcc8c4f6c 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -11024,12 +11024,31 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info, struct fstrim_range *range)
> int ret = 0;
>
> /*
> - * try to trim all FS space, our block group may start from non-zero.
> + * NOTE: Btrfs uses its own logical address space, where its first
> + * chunk can start anywhere if it wants.
> + * If we follow common start = 0 and len = fs_size from @range, we
> + * can end up without trimming any block groups, since it's highly
> + * possible all chunks start beyond that range.
> + *
> + * So if we want to trim the whole fs, extent the len to (u64)-1 to trim
> + * all block groups.
> + *
> + * Also, since @range will always be truncated to fs size, manually
> + * passing range to trim specified range doesn't make much sense.
> + * (No mean to trim any block group whose bytenr starts beyond
> + * @total_bytes)
> + * So in that case, return -ENOTTY directly to prevent any custom trim
> + * request.
> */
> - if (range->len == total_bytes)
> - cache = btrfs_lookup_first_block_group(fs_info, range->start);
> - else
> - cache = btrfs_lookup_block_group(fs_info, range->start);
> + if (range->start == 0 && range->len == total_bytes) {
> + range->len = (u64)-1;
After the fs_trim program gets the value for the range's length and
before it invokes the trim ioctl, the value might have changed,
resulting in returning the enotty error below.
> + } else {
> + btrfs_info(fs_info,
> + "trimming custom range is not supported due to the limitation of fstrim_range");
I can't understand this message, and I doubt the average user/admin can.
To me it seems this can be a lot more simple by ignoring the range,
that is, always considering [0, (u64)-1[. After all, due to the way
btrfs organizes space, the range does not make any sense and I doubt
users/programs will have all the necessary knowledge and willing to
compute a range that makes sense to btrfs based on the current block
group layout of the fs...
> + return -ENOTTY;
> + }
> +
> + cache = btrfs_lookup_first_block_group(fs_info, range->start);
>
> for (; cache; cache = next_block_group(fs_info, cache)) {
> if (cache->key.objectid >= (range->start + range->len)) {
> --
> 2.15.0
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
