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, 14 insertions, 11 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 64b52be6bf0b..91aeac36ebc9 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1430,7 +1430,7 @@ static inline int scrub_nr_raid_mirrors(struct btrfs_io_context *bioc)
 }
 
 static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
-						 u64 *raid_map,
+						 u64 full_stripe_logical,
 						 int nstripes, int mirror,
 						 int *stripe_index,
 						 u64 *stripe_offset)
@@ -1438,19 +1438,22 @@ static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
 	int i;
 
 	if (map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		const int nr_data_stripes = (map_type & BTRFS_BLOCK_GROUP_RAID5) ?
+					    nstripes - 1 : nstripes - 2;
+
 		/* RAID5/6 */
-		for (i = 0; i < nstripes; i++) {
-			if (raid_map[i] == RAID6_Q_STRIPE ||
-			    raid_map[i] == RAID5_P_STRIPE)
-				continue;
+		for (i = 0; i < nr_data_stripes; i++) {
+			const u64 data_stripe_start = full_stripe_logical +
+						(i * BTRFS_STRIPE_LEN);
 
-			if (logical >= raid_map[i] &&
-			    logical < raid_map[i] + BTRFS_STRIPE_LEN)
+			if (logical >= data_stripe_start &&
+			    logical < data_stripe_start + BTRFS_STRIPE_LEN)
 				break;
 		}
 
 		*stripe_index = i;
-		*stripe_offset = logical - raid_map[i];
+		*stripe_offset = (logical - full_stripe_logical) &
+				 BTRFS_STRIPE_LEN_MASK;
 	} else {
 		/* The other RAID type */
 		*stripe_index = mirror;
@@ -1538,7 +1541,7 @@ static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
 
 			scrub_stripe_index_and_offset(logical,
 						      bioc->map_type,
-						      bioc->raid_map,
+						      bioc->full_stripe_logical,
 						      bioc->num_stripes -
 						      bioc->replace_nr_stripes,
 						      mirror_index,
@@ -2398,7 +2401,7 @@ static void scrub_missing_raid56_pages(struct scrub_block *sblock)
 	btrfs_bio_counter_inc_blocked(fs_info);
 	ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS, logical,
 			       &length, &bioc);
-	if (ret || !bioc || !bioc->raid_map)
+	if (ret || !bioc)
 		goto bioc_out;
 
 	if (WARN_ON(!sctx->is_dev_replace ||
@@ -3007,7 +3010,7 @@ static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
 	btrfs_bio_counter_inc_blocked(fs_info);
 	ret = btrfs_map_sblock(fs_info, BTRFS_MAP_WRITE, sparity->logic_start,
 			       &length, &bioc);
-	if (ret || !bioc || !bioc->raid_map)
+	if (ret || !bioc)
 		goto bioc_out;
 
 	bio = bio_alloc(NULL, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);