btrfs: use integrated bitmaps for btrfs_raid_bio::dbitmap and finish_pbitmap

Previsouly we use "unsigned long *" for those two bitmaps.

But since we only support fixed stripe length (64KiB, already checked in
tree-checker), "unsigned long *" is really a waste of memory, while we
can just use "unsigned long".

This saves us 8 bytes in total for btrfs_raid_bio.

To be extra safe, add an ASSERT() making sure calculated
@stripe_nsectors is always smaller than BITS_PER_LONG.

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

fs/btrfs/raid56.c

@@ -164,6 +164,13 @@ struct btrfs_raid_bio {
 	atomic_t stripes_pending;
 
 	atomic_t error;
+
+	/* Bitmap to record which horizontal stripe has data */
+	unsigned long dbitmap;
+
+	/* Allocated with stripe_nsectors-many bits for finish_*() calls */
+	unsigned long finish_pbitmap;
+
 	/*
 	 * these are two arrays of pointers.  We allocate the
 	 * rbio big enough to hold them both and setup their
@@ -184,14 +191,8 @@ struct btrfs_raid_bio {
 	 */
 	struct sector_ptr *stripe_sectors;
 
-	/* Bitmap to record which horizontal stripe has data */
-	unsigned long *dbitmap;
-
 	/* allocated with real_stripes-many pointers for finish_*() calls */
 	void **finish_pointers;
-
-	/* Allocated with stripe_nsectors-many bits for finish_*() calls */
-	unsigned long *finish_pbitmap;
 };
 
 static int __raid56_parity_recover(struct btrfs_raid_bio *rbio);
@@ -1038,14 +1039,17 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 	ASSERT(IS_ALIGNED(stripe_len, PAGE_SIZE));
 	/* PAGE_SIZE must also be aligned to sectorsize for subpage support */
 	ASSERT(IS_ALIGNED(PAGE_SIZE, fs_info->sectorsize));
+	/*
+	 * Our current stripe len should be fixed to 64k thus stripe_nsectors
+	 * (at most 16) should be no larger than BITS_PER_LONG.
+	 */
+	ASSERT(stripe_nsectors <= BITS_PER_LONG);
 
 	rbio = kzalloc(sizeof(*rbio) +
 		       sizeof(*rbio->stripe_pages) * num_pages +
 		       sizeof(*rbio->bio_sectors) * num_sectors +
 		       sizeof(*rbio->stripe_sectors) * num_sectors +
-		       sizeof(*rbio->finish_pointers) * real_stripes +
+		       sizeof(*rbio->finish_pointers) * real_stripes,
-		       sizeof(*rbio->dbitmap) * BITS_TO_LONGS(stripe_nsectors) +
-		       sizeof(*rbio->finish_pbitmap) * BITS_TO_LONGS(stripe_nsectors),
 		       GFP_NOFS);
 	if (!rbio)
 		return ERR_PTR(-ENOMEM);
@@ -1081,8 +1085,6 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 	CONSUME_ALLOC(rbio->bio_sectors, num_sectors);
 	CONSUME_ALLOC(rbio->stripe_sectors, num_sectors);
 	CONSUME_ALLOC(rbio->finish_pointers, real_stripes);
-	CONSUME_ALLOC(rbio->dbitmap, BITS_TO_LONGS(stripe_nsectors));
-	CONSUME_ALLOC(rbio->finish_pbitmap, BITS_TO_LONGS(stripe_nsectors));
 #undef  CONSUME_ALLOC
 
 	if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID5)
@@ -1939,7 +1941,7 @@ static void __raid_recover_end_io(struct btrfs_raid_bio *rbio)
 		 * which we have data when doing parity scrub.
 		 */
 		if (rbio->operation == BTRFS_RBIO_PARITY_SCRUB &&
-		    !test_bit(sectornr, rbio->dbitmap))
+		    !test_bit(sectornr, &rbio->dbitmap))
 			continue;
 
 		/*
@@ -2374,7 +2376,7 @@ struct btrfs_raid_bio *raid56_parity_alloc_scrub_rbio(struct bio *bio,
 	}
 	ASSERT(i < rbio->real_stripes);
 
-	bitmap_copy(rbio->dbitmap, dbitmap, stripe_nsectors);
+	bitmap_copy(&rbio->dbitmap, dbitmap, stripe_nsectors);
 
 	/*
 	 * We have already increased bio_counter when getting bioc, record it
@@ -2412,7 +2414,7 @@ static int alloc_rbio_essential_pages(struct btrfs_raid_bio *rbio)
 	int stripe;
 	int sectornr;
 
-	for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
+	for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
 		for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
 			struct page *page;
 			int index = (stripe * rbio->stripe_nsectors + sectornr) *
@@ -2437,7 +2439,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 	struct btrfs_io_context *bioc = rbio->bioc;
 	const u32 sectorsize = bioc->fs_info->sectorsize;
 	void **pointers = rbio->finish_pointers;
-	unsigned long *pbitmap = rbio->finish_pbitmap;
+	unsigned long *pbitmap = &rbio->finish_pbitmap;
 	int nr_data = rbio->nr_data;
 	int stripe;
 	int sectornr;
@@ -2460,7 +2462,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 
 	if (bioc->num_tgtdevs && bioc->tgtdev_map[rbio->scrubp]) {
 		is_replace = 1;
-		bitmap_copy(pbitmap, rbio->dbitmap, rbio->stripe_nsectors);
+		bitmap_copy(pbitmap, &rbio->dbitmap, rbio->stripe_nsectors);
 	}
 
 	/*
@@ -2497,7 +2499,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 	/* Map the parity stripe just once */
 	pointers[nr_data] = kmap_local_page(p_sector.page);
 
-	for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
+	for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
 		struct sector_ptr *sector;
 		void *parity;
 
@@ -2525,7 +2527,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 			memcpy(parity, pointers[rbio->scrubp], sectorsize);
 		else
 			/* Parity is right, needn't writeback */
-			bitmap_clear(rbio->dbitmap, sectornr, 1);
+			bitmap_clear(&rbio->dbitmap, sectornr, 1);
 		kunmap_local(parity);
 
 		for (stripe = nr_data - 1; stripe >= 0; stripe--)
@@ -2547,7 +2549,7 @@ writeback:
 	 * higher layers (the bio_list in our rbio) and our p/q.  Ignore
 	 * everything else.
 	 */
-	for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
+	for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
 		struct sector_ptr *sector;
 
 		sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
@@ -2714,7 +2716,7 @@ static void raid56_parity_scrub_stripe(struct btrfs_raid_bio *rbio)
 	 * stripe
 	 */
 	for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
-		for_each_set_bit(sectornr , rbio->dbitmap, rbio->stripe_nsectors) {
+		for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
 			struct sector_ptr *sector;
 			/*
 			 * We want to find all the sectors missing from the