On 16.08.19 г. 18:20 ч., Josef Bacik wrote:
> It made sense to have the global reserve set at 16M in the past, but
> since it is used less nowadays set the minimum size to the number of
> items we'll need to update the main trees we update during a transaction
> commit, plus some slop area so we can do unlinks if we need to.
>
> In practice this doesn't affect normal file systems, but for xfstests
> where we do things like fill up a fs and then rm * it can fall over in
> weird ways. This enables us for more sane behavior at extremely small
> file system sizes.
>
> Signed-off-by: Josef Bacik <[email protected]>
> ---
> fs/btrfs/block-rsv.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
> index c64b460a4301..657675eef443 100644
> --- a/fs/btrfs/block-rsv.c
> +++ b/fs/btrfs/block-rsv.c
> @@ -258,6 +258,7 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info
> *fs_info)
> struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
> struct btrfs_space_info *sinfo = block_rsv->space_info;
> u64 num_bytes;
> + unsigned min_items;
>
> /*
> * The global block rsv is based on the size of the extent tree, the
> @@ -267,7 +268,26 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info
> *fs_info)
> num_bytes = btrfs_root_used(&fs_info->extent_root->root_item) +
> btrfs_root_used(&fs_info->csum_root->root_item) +
> btrfs_root_used(&fs_info->tree_root->root_item);
> - num_bytes = max_t(u64, num_bytes, SZ_16M);
> +
> + /*
> + * We at a minimum are going to modify the csum root, the tree root, and
> + * the extent root.
> + */
> + min_items = 3;
> +
> + /*
> + * But we also want to reserve enough space so we can do the fallback
> + * global reserve for an unlink, which is an additional 5 items (see the
> + * comment in __unlink_start_trans for what we're modifying.)
> + *
> + * But we also need space for the delayed ref updates from the unlink,
> + * so its 10, 5 for the actual operation, and 5 for the delayed ref
> + * updates.
> + */
> + min_items += 10;
> +
> + num_bytes = max_t(u64, num_bytes,
> + btrfs_calc_insert_metadata_size(fs_info, min_items));
For ordinary, 16k nodesize filesystem, btrfs_calc_insert_metadata_size
will really return 3.4m -> 16 * 8 * 2 * 13 * 1024 = 3407872 bytes . In
those cases I expect that the code will always be doing num_bytes =
num_bytes.
>
> spin_lock(&sinfo->lock);
> spin_lock(&block_rsv->lock);
>
