On 21.11.18 г. 21:03 ч., Josef Bacik wrote:
> With my change to no longer take into account the global reserve for
> metadata allocation chunks we have this side-effect for mixed block
> group fs'es where we are no longer allocating enough chunks for the
> data/metadata requirements. To deal with this add a ALLOC_CHUNK_FORCE
> step to the flushing state machine. This will only get used if we've
> already made a full loop through the flushing machinery and tried
> committing the transaction. If we have then we can try and force a
> chunk allocation since we likely need it to make progress. This
> resolves the issues I was seeing with the mixed bg tests in xfstests
> with my previous patch.
>
> Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
Still, my observation is that the metadata reclaim code is increasing in
complexity for rather niche use cases or the details become way too subtle.
> ---
> fs/btrfs/ctree.h | 3 ++-
> fs/btrfs/extent-tree.c | 18 +++++++++++++++++-
> include/trace/events/btrfs.h | 1 +
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 0c6d589c8ce4..8ccc5019172b 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2750,7 +2750,8 @@ enum btrfs_flush_state {
> FLUSH_DELALLOC = 5,
> FLUSH_DELALLOC_WAIT = 6,
> ALLOC_CHUNK = 7,
> - COMMIT_TRANS = 8,
> + ALLOC_CHUNK_FORCE = 8,
> + COMMIT_TRANS = 9,
> };
>
> int btrfs_alloc_data_chunk_ondemand(struct btrfs_inode *inode, u64 bytes);
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index a91b3183dcae..e6bb6ce23c84 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4927,6 +4927,7 @@ static void flush_space(struct btrfs_fs_info *fs_info,
> btrfs_end_transaction(trans);
> break;
> case ALLOC_CHUNK:
> + case ALLOC_CHUNK_FORCE:
> trans = btrfs_join_transaction(root);
> if (IS_ERR(trans)) {
> ret = PTR_ERR(trans);
> @@ -4934,7 +4935,9 @@ static void flush_space(struct btrfs_fs_info *fs_info,
> }
> ret = do_chunk_alloc(trans,
> btrfs_metadata_alloc_profile(fs_info),
> - CHUNK_ALLOC_NO_FORCE);
> + (state == ALLOC_CHUNK) ?
> + CHUNK_ALLOC_NO_FORCE :
> + CHUNK_ALLOC_FORCE);
> btrfs_end_transaction(trans);
> if (ret > 0 || ret == -ENOSPC)
> ret = 0;
> @@ -5070,6 +5073,19 @@ static void btrfs_async_reclaim_metadata_space(struct
> work_struct *work)
> commit_cycles--;
> }
>
> + /*
> + * We don't want to force a chunk allocation until we've tried
> + * pretty hard to reclaim space. Think of the case where we
> + * free'd up a bunch of space and so have a lot of pinned space
> + * to reclaim. We would rather use that than possibly create a
> + * underutilized metadata chunk. So if this is our first run
> + * through the flushing state machine skip ALLOC_CHUNK_FORCE and
> + * commit the transaction. If nothing has changed the next go
> + * around then we can force a chunk allocation.
> + */
> + if (flush_state == ALLOC_CHUNK_FORCE && !commit_cycles)
> + flush_state++;
> +
> if (flush_state > COMMIT_TRANS) {
> commit_cycles++;
> if (commit_cycles > 2) {
> diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
> index 63d1f9d8b8c7..dd0e6f8d6b6e 100644
> --- a/include/trace/events/btrfs.h
> +++ b/include/trace/events/btrfs.h
> @@ -1051,6 +1051,7 @@ TRACE_EVENT(btrfs_trigger_flush,
> { FLUSH_DELAYED_REFS_NR, "FLUSH_DELAYED_REFS_NR"},
> \
> { FLUSH_DELAYED_REFS, "FLUSH_ELAYED_REFS"},
> \
> { ALLOC_CHUNK, "ALLOC_CHUNK"},
> \
> + { ALLOC_CHUNK_FORCE, "ALLOC_CHUNK_FORCE"},
> \
> { COMMIT_TRANS, "COMMIT_TRANS"})
>
> TRACE_EVENT(btrfs_flush_space,
>
