On 3.12.18 г. 17:24 ч., Josef Bacik wrote:
> We could generate a lot of delayed refs in evict but never have any left
> over space from our block rsv to make up for that fact. So reserve some
> extra space and give it to the transaction so it can be used to refill
> the delayed refs rsv every loop through the truncate path.
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/inode.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 623a71d871d4..8ac7abe2ae9b 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5258,13 +5258,15 @@ static struct btrfs_trans_handle *evict_refill_and_join(struct btrfs_root *root,
> {
> struct btrfs_fs_info *fs_info = root->fs_info;
> struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
> + u64 delayed_refs_extra = btrfs_calc_trans_metadata_size(fs_info, 1);
> int failures = 0;
>
> for (;;) {
> struct btrfs_trans_handle *trans;
> int ret;
>
> - ret = btrfs_block_rsv_refill(root, rsv, rsv->size,
> + ret = btrfs_block_rsv_refill(root, rsv,
> + rsv->size + delayed_refs_extra,
> BTRFS_RESERVE_FLUSH_LIMIT);
Rather than having to play those tricks, why not just modify the call in
btrfs_evict_inode, from:
rsv->size = btrfs_calc_trunc_metadata_size(fs_info, 1);
to
rsv->size = btrfs_calc_trunc_metadata_size(fs_info, 2);
and add a comment what the number 2 means of course.
>
> if (ret && ++failures > 2) {
> @@ -5273,9 +5275,28 @@ static struct btrfs_trans_handle *evict_refill_and_join(struct btrfs_root *root,
> return ERR_PTR(-ENOSPC);
> }
>
> + /*
> + * Evict can generate a large amount of delayed refs without
> + * having a way to add space back since we exhaust our temporary
> + * block rsv. We aren't allowed to do FLUSH_ALL in this case
> + * because we could deadlock with so many things in the flushing
> + * code, so we have to try and hold some extra space to
> + * compensate for our delayed ref generation. If we can't get
> + * that space then we need see if we can steal our minimum from
> + * the global reserve. We will be ratelimited by the amount of
> + * space we have for the delayed refs rsv, so we'll end up
> + * committing and trying again.
> + */
> trans = btrfs_join_transaction(root);
> - if (IS_ERR(trans) || !ret)
> + if (IS_ERR(trans) || !ret) {
> + if (!IS_ERR(trans)) {
> + trans->block_rsv = &fs_info->trans_block_rsv;
This line is redundant since evict_refill_and_join is called before the
trans->block_rsv is modified.
> + trans->bytes_reserved = delayed_refs_extra;
Is this even correct, since we join a transaction it might have already
had some bytes reserved. So in anycase shouldn't the line here say:
trans->bytes_reserved += delayed_refs_extra ?
> + btrfs_block_rsv_migrate(rsv, trans->block_rsv,
> + delayed_refs_extra, 1);
> + }
> return trans;
> + }
>
> /*
> * Try to steal from the global reserve if there is space for
>
