btrfs: remove btrfs_end_io_wq
All reads bio that go through btrfs_map_bio need to be completed in
user context. And read I/Os are the most common and timing critical
in almost any file system workloads.
Embed a work_struct into struct btrfs_bio and use it to complete all
read bios submitted through btrfs_map, using the REQ_META flag to decide
which workqueue they are placed on.
This removes the need for a separate 128 byte allocation (typically
rounded up to 192 bytes by slab) for all reads with a size increase
of 24 bytes for struct btrfs_bio. Future patches will reorganize
struct btrfs_bio to make use of this extra space for writes as well.
(All sizes are based a on typical 64-bit non-debug build)
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 1e86c48..7973d11 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -371,6 +371,9 @@ struct btrfs_bio {
u8 csum_inline[BTRFS_BIO_INLINE_CSUM_SIZE];
struct bvec_iter iter;
+ /* For read end I/O handling */
+ struct work_struct end_io_work;
+
/*
* This member must come last, bio_alloc_bioset will allocate enough
* bytes for entire btrfs_bio but relies on bio being last.
