Re: [PATCH v4] btrfs: zoned: don't force read-only on transient -EAGAIN from reloc merge

On Mon, Jun 22, 2026 at 9:27 AM Johannes Thumshirn
<[email protected]> wrote:
>
> On a zoned FS, btrfs_delayed_refs_rsv_refill() returns -EAGAIN whenever
> the over-committed metadata plus the zone_unusable bytes exceeds the
> usable size in a metadata block-group to avoid heavy over-commit of
> metadata and early ENOSPC in one transaction.
>
> If this happens while doing reclaim, the transaction is getting
> aborted.
>
> Treat -EAGAIN as a soft, retryable condition in case of block-group
> reclaim.
>
> Reported-by: Damien Le Moal <[email protected]>
> Fixes: 7bcb04de982f ("btrfs: zoned: cap delayed refs metadata reservation to avoid overcommit")
> Signed-off-by: Johannes Thumshirn <[email protected]>
> ---
> Changes to v3:
> - Don't ASSERT() for zoned in case of EAGAIN in
>   btrfs_reclaim_block_group but check for zoned
>
>  fs/btrfs/block-group.c | 10 +++++++-
>  fs/btrfs/relocation.c  | 52 ++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 57 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index ab76a5173272..1327fd526b06 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -2047,6 +2047,12 @@ static int btrfs_reclaim_block_group(struct btrfs_block_group *bg, int *reclaime
>
>         trace_btrfs_reclaim_block_group(bg);
>         ret = btrfs_relocate_chunk(fs_info, bg->start, false);
> +       if (btrfs_is_zoned(fs_info) && ret == -EAGAIN) {
> +               btrfs_dec_block_group_ro(bg);
> +               btrfs_debug(fs_info, "deferring reclaim of chunk %llu",
> +                           bg->start);
> +               return ret;
> +       }
>         if (ret) {
>                 btrfs_dec_block_group_ro(bg);
>                 btrfs_err(fs_info, "error relocating chunk %llu",
> @@ -2113,7 +2119,9 @@ void btrfs_reclaim_block_groups(struct btrfs_fs_info *fs_info, unsigned int limi
>                 spin_unlock(&fs_info->unused_bgs_lock);
>                 ret = btrfs_reclaim_block_group(bg, &reclaimed);
>
> -               if (ret && !READ_ONCE(space_info->periodic_reclaim))
> +               if (ret == -EAGAIN)
> +                       btrfs_link_bg_list(bg, &retry_list);
> +               else if (ret && !READ_ONCE(space_info->periodic_reclaim))
>                         btrfs_link_bg_list(bg, &retry_list);
>                 btrfs_put_block_group(bg);
>
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 1819d49d19c3..73d9948b5382 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1530,6 +1530,36 @@ static void clear_reloc_root(struct btrfs_root *root)
>         clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
>  }
>
> +/* Drop the reloc trees of a relocation that is being deferred and retried */

Same comment as in v3: always add punctuation to sentences, this is
our preferred style.

> +static void abort_reloc_roots(struct reloc_control *rc, struct list_head *list)
> +{
> +       struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
> +       struct btrfs_root *reloc_root, *tmp;
> +
> +       list_for_each_entry_safe(reloc_root, tmp, list, root_list) {
> +               struct btrfs_root *root;
> +
> +               root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset,
> +                                        false);
> +               if (!IS_ERR(root)) {
> +                       if (root->reloc_root == reloc_root) {
> +                               clear_reloc_root(root);
> +                               btrfs_put_root(reloc_root);
> +                       }
> +                       btrfs_put_root(root);
> +               }
> +
> +               btrfs_set_root_refs(&reloc_root->root_item, 0);
> +               memset(&reloc_root->root_item.drop_progress, 0,
> +                      sizeof(struct btrfs_disk_key));
> +               btrfs_set_root_drop_level(&reloc_root->root_item, 0);
> +
> +               list_del_init(&reloc_root->root_list);
> +               list_add_tail(&reloc_root->reloc_dirty_list,
> +                               &rc->dirty_subvol_roots);
> +       }
> +}
> +
>  static int clean_dirty_subvols(struct reloc_control *rc)
>  {
>         struct btrfs_root *root;
> @@ -1869,8 +1899,9 @@ int prepare_to_merge(struct reloc_control *rc, int err)
>         return err;
>  }
>
> +

Same comment as in v3: stray, accidental, new line.

>  static noinline_for_stack
> -void merge_reloc_roots(struct reloc_control *rc)
> +int merge_reloc_roots(struct reloc_control *rc)
>  {
>         struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
>         struct btrfs_root *root;
> @@ -1968,7 +1999,15 @@ void merge_reloc_roots(struct reloc_control *rc)
>                 goto again;
>         }
>  out:
> -       if (ret) {
> +       if (ret == -EAGAIN) {

As pointed in v3, missing an:    && (btrfs_is_zoned(fs_info)

> +               abort_reloc_roots(rc, &reloc_roots);
> +
> +               /* new reloc root may be added */

Same comment as in v3: always capitalize the first word and add
punctuation to sentences, this is our preferred style.

Otherwise it looks fine, thanks.

> +               mutex_lock(&fs_info->reloc_mutex);
> +               list_splice_init(&rc->reloc_roots, &reloc_roots);
> +               mutex_unlock(&fs_info->reloc_mutex);
> +               abort_reloc_roots(rc, &reloc_roots);
> +       } else if (ret) {
>                 btrfs_handle_fs_error(fs_info, ret, NULL);
>                 free_reloc_roots(&reloc_roots);
>
> @@ -1994,6 +2033,7 @@ void merge_reloc_roots(struct reloc_control *rc)
>          *
>          * The remaining nodes will be cleaned up by put_reloc_control().
>          */
> +       return ret;
>  }
>
>  static void free_block_list(struct rb_root *blocks)
> @@ -3723,7 +3763,9 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
>          */
>         err = prepare_to_merge(rc, err);
>
> -       merge_reloc_roots(rc);
> +       ret = merge_reloc_roots(rc);
> +       if (ret && !err)
> +               err = ret;
>
>         rc->merge_reloc_tree = false;
>         unset_reloc_control(rc);
> @@ -5692,7 +5734,9 @@ int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
>         if (ret)
>                 goto out_unset;
>
> -       merge_reloc_roots(rc);
> +       ret = merge_reloc_roots(rc);
> +       if (ret)
> +               goto out_unset;
>
>         unset_reloc_control(rc);
>
> --
> 2.54.0
>
>