btrfs: replace btrfs_io_context::raid_map with a fixed u64 value

In btrfs_io_context structure, we have a pointer raid_map, which
indicates the logical bytenr for each stripe.

But considering we always call sort_parity_stripes(), the result
raid_map[] is always sorted, thus raid_map[0] is always the logical
bytenr of the full stripe.

So why we waste the space and time (for sorting) for raid_map?

This patch will replace btrfs_io_context::raid_map with a single u64
number, full_stripe_start, by:

- Replace btrfs_io_context::raid_map with full_stripe_start

- Replace call sites using raid_map[0] to use full_stripe_start

- Replace call sites using raid_map[i] to compare with nr_data_stripes.

The benefits are:

- Less memory wasted on raid_map
  It's sizeof(u64) * num_stripes vs sizeof(u64).
  It'll always save at least one u64, and the benefit grows larger with
  num_stripes.

- No more weird alloc_btrfs_io_context() behavior
  As there is only one fixed size + one variable length array.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index 75d7d22c3a27..8ea9cea9bfeb 100644
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -2422,7 +2422,7 @@ DECLARE_EVENT_CLASS(btrfs_raid56_bio,
 	),
 
 	TP_fast_assign_btrfs(rbio->bioc->fs_info,
-		__entry->full_stripe	= rbio->bioc->raid_map[0];
+		__entry->full_stripe	= rbio->bioc->full_stripe_logical;
 		__entry->physical	= bio->bi_iter.bi_sector << SECTOR_SHIFT;
 		__entry->len		= bio->bi_iter.bi_size;
 		__entry->opf		= bio_op(bio);