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On 6/11/15 11:20 AM, jeffm@xxxxxxxx wrote:
> From: Jeff Mahoney <jeffm@xxxxxxxx>
>
> Btrfs doesn't track superblocks with extent records so there is
> nothing persistent on-disk to indicate that those blocks are in
> use. We track the superblocks in memory to ensure they don't get
> used by removing them from the free space cache when we load a
> block group from disk. Prior to 47ab2a6c6a (Btrfs: remove empty
> block groups automatically), that was fine since the block group
> would never be reclaimed so the superblock was always safe. Once
> we started removing the empty block groups, we were protected by
> the fact that discards weren't being properly issued for unused
> space either via FITRIM or -odiscard. The block groups were still
> being released, but the blocks remained on disk.
>
> In order to properly discard unused block groups, we need to filter
> out the superblocks from the discard range. Superblocks are
> located at fixed locations on each device, so it makes sense to
> filter them out in btrfs_issue_discard, which is used by both
> -odiscard and FITRIM.
>
> Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx> ---
> fs/btrfs/extent-tree.c | 50
> ++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed,
> 44 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index
> 0ec3acd..75d0226 100644 --- a/fs/btrfs/extent-tree.c +++
> b/fs/btrfs/extent-tree.c @@ -1884,10 +1884,47 @@ static int
> remove_extent_backref(struct btrfs_trans_handle *trans, return
> ret; }
>
> -static int btrfs_issue_discard(struct block_device *bdev, - u64
> start, u64 len) +#define in_range(b, first, len) ((b) >= (first) &&
> (b) < (first) + (len)) +static int btrfs_issue_discard(struct
> block_device *bdev, u64 start, u64 len, + u64
> *discarded_bytes) { - return blkdev_issue_discard(bdev, start >> 9,
> len >> 9, GFP_NOFS, 0); + u64 skipped = 0; + u64 bytes_left = len;
> + int ret = 0 , j; + + *discarded_bytes = 0; + + /* Skip any
> superblocks on this device. */ + for (j = 0; j <
> BTRFS_SUPER_MIRROR_MAX; j++) { + u64 sb_offset =
> btrfs_sb_offset(j); + u64 size = sb_offset - start; + + if
> (!in_range(sb_offset, start, bytes_left)) + continue; + + if
> (size) { + ret = blkdev_issue_discard(bdev, start >> 9, size >>
> 9, + GFP_NOFS, 0); + if (!ret) + *discarded_bytes +=
> size; + else if (ret != -EOPNOTSUPP) + return ret; + } + +
> start = sb_offset + BTRFS_SUPER_INFO_SIZE; + if (start > len) +
> start = len; + bytes_left = len - start; + skipped +=
> BTRFS_SUPER_INFO_SIZE;
Whoops. This is an unused artifact from an earlier version.
- -Jeff
> + } + + if (bytes_left) { + ret = blkdev_issue_discard(bdev, start
> >> 9, bytes_left >> 9, + GFP_NOFS, 0); + if (!ret) +
> *discarded_bytes += bytes_left; + } + return ret; }
>
> int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr, @@
> -1906,16 +1943,17 @@ int btrfs_discard_extent(struct btrfs_root
> *root, u64 bytenr, struct btrfs_bio_stripe *stripe =
> bbio->stripes; int i;
>
> - for (i = 0; i < bbio->num_stripes; i++, stripe++) { + u64
> bytes; + if (!stripe->dev->can_discard) continue;
>
> ret = btrfs_issue_discard(stripe->dev->bdev, stripe->physical, -
> stripe->length); + stripe->length, &bytes); if (!ret) -
> discarded_bytes += stripe->length; + discarded_bytes += bytes;
> else if (ret != -EOPNOTSUPP) break; /* Logic errors or -ENOMEM, or
> -EIO but I don't know how that could happen JDM */
>
>
- --
Jeff Mahoney
SUSE Labs
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