On 3.12.18 г. 17:24 ч., Josef Bacik wrote:
> With severe fragmentation we can end up with our inode rsv size being
> huge during writeout, which would cause us to need to make very large
> metadata reservations. However we may not actually need that much once
The sentence beginning with "However" needs more information, why might
we not need that much once writeout is complete?
> writeout is complete. So instead try to make our reservation, and if we
> couldn't make it re-calculate our new reservation size and try again.
Why do you think that recalculating the requested bytes will be
different the 2nd time ?
> If our reservation size doesn't change between tries then we know we are
> actually out of space and can error out.
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 58 +++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 43 insertions(+), 15 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 0ee77a98f867..0e1a499035ac 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -5787,6 +5787,21 @@ int btrfs_block_rsv_refill(struct btrfs_root *root,
> return ret;
> }
>
> +static inline void __get_refill_bytes(struct btrfs_block_rsv *block_rsv,
> + u64 *metadata_bytes, u64 *qgroup_bytes)
This function needs a better name. Something like calc_required_bytes or
calc_refill_bytes
> +{
> + *metadata_bytes = 0;
> + *qgroup_bytes = 0;
> +
> + spin_lock(&block_rsv->lock);
> + if (block_rsv->reserved < block_rsv->size)
> + *metadata_bytes = block_rsv->size - block_rsv->reserved;
> + if (block_rsv->qgroup_rsv_reserved < block_rsv->qgroup_rsv_size)
> + *qgroup_bytes = block_rsv->qgroup_rsv_size -
> + block_rsv->qgroup_rsv_reserved;
> + spin_unlock(&block_rsv->lock);
> +}
> +
> /**
> * btrfs_inode_rsv_refill - refill the inode block rsv.
> * @inode - the inode we are refilling.
> @@ -5802,25 +5817,39 @@ static int btrfs_inode_rsv_refill(struct btrfs_inode *inode,
> {
> struct btrfs_root *root = inode->root;
> struct btrfs_block_rsv *block_rsv = &inode->block_rsv;
> - u64 num_bytes = 0;
> + u64 num_bytes = 0, last = 0;
> u64 qgroup_num_bytes = 0;
> int ret = -ENOSPC;
>
> - spin_lock(&block_rsv->lock);
> - if (block_rsv->reserved < block_rsv->size)
> - num_bytes = block_rsv->size - block_rsv->reserved;
> - if (block_rsv->qgroup_rsv_reserved < block_rsv->qgroup_rsv_size)
> - qgroup_num_bytes = block_rsv->qgroup_rsv_size -
> - block_rsv->qgroup_rsv_reserved;
> - spin_unlock(&block_rsv->lock);
> -
> + __get_refill_bytes(block_rsv, &num_bytes, &qgroup_num_bytes);
> if (num_bytes == 0)
> return 0;
>
> - ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_num_bytes, true);
> - if (ret)
> - return ret;
> - ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
> + do {
> + ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_num_bytes, true);
> + if (ret)
> + return ret;
> + ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
> + if (ret) {
> + btrfs_qgroup_free_meta_prealloc(root, qgroup_num_bytes);
> + last = num_bytes;
> + /*
> + * If we are fragmented we can end up with a lot of
> + * outstanding extents which will make our size be much
> + * larger than our reserved amount. If we happen to
> + * try to do a reservation here that may result in us
> + * trying to do a pretty hefty reservation, which we may
> + * not need once delalloc flushing happens. If this is
The "If we happen" sentence needs to be reworded because it's -ENOPARSE.
Perhaps one of the "to do a reservation" should go away?
> + * the case try and do the reserve again.
> + */
> + if (flush == BTRFS_RESERVE_FLUSH_ALL)
> + __get_refill_bytes(block_rsv, &num_bytes,
> + &qgroup_num_bytes);
> + if (num_bytes == 0)
> + return 0;
> + }
> + } while (ret && last != num_bytes);
> +
> if (!ret) {
> block_rsv_add_bytes(block_rsv, num_bytes, false);
> trace_btrfs_space_reservation(root->fs_info, "delalloc",
> @@ -5830,8 +5859,7 @@ static int btrfs_inode_rsv_refill(struct btrfs_inode *inode,
> spin_lock(&block_rsv->lock);
> block_rsv->qgroup_rsv_reserved += qgroup_num_bytes;
> spin_unlock(&block_rsv->lock);
> - } else
> - btrfs_qgroup_free_meta_prealloc(root, qgroup_num_bytes);
> + }
> return ret;
> }
>
>
