btrfs: scrub: reduce memory usage of struct scrub_sector_verification

That structure records needed info for block verification (either data
checksum pointer, or expected tree block generation).

But there is also a boolean to tell if this block belongs to a metadata
or not, as the data checksum pointer and expected tree block generation
is already a union, we need a dedicated bit to tell if this block is a
metadata or not.

However such layout means we're wasting 63 bits for x86_64, which is a
huge memory waste.

Thanks to the recent bitmap aggregation, we can easily move this
single-bit-per-block member to a new sub-bitmap.
And since we already have six 16 bits long bitmaps, adding another
bitmap won't even increase any memory usage for x86_64, as we need two
64 bits long anyway.

This will reduce the following memory usages:

- sizeof(struct scrub_sector_verification)
  From 16 bytes to 8 bytes on x86_64.

- scrub_stripe::sectors
  From 16 * 16 to 16 * 8 bytes.

- Per-device scrub_ctx memory usage
  From 128 * (16 * 16) to 128 * (16 * 8), which saves 16KiB memory.

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

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index c18d903027d9ad710b4de75d0cd7ad24c759dbad..ed120621021b0bd2d01b410078e03a260ba8ca81 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -66,8 +66,6 @@ struct scrub_ctx;
 
 /* Represent one sector and its needed info to verify the content. */
 struct scrub_sector_verification {
-       bool is_metadata;
-
        union {
                /*
                 * Csum pointer for data csum verification.  Should point to a
@@ -115,6 +113,9 @@ enum {
        /* Which blocks are covered by extent items. */
        scrub_bitmap_nr_has_extent = 0,
 
+       /* Which blocks are meteadata. */
+       scrub_bitmap_nr_is_metadata,
+
        /*
         * Which blocks have errors, including IO, csum, and metadata
         * errors.
@@ -304,6 +305,7 @@ static inline unsigned int scrub_bitmap_weight_##name(struct scrub_stripe *strip
        return bitmap_weight(&bitmap, stripe->nr_sectors);              \
 }
 IMPLEMENT_SCRUB_BITMAP_OPS(has_extent);
+IMPLEMENT_SCRUB_BITMAP_OPS(is_metadata);
 IMPLEMENT_SCRUB_BITMAP_OPS(error);
 IMPLEMENT_SCRUB_BITMAP_OPS(io_error);
 IMPLEMENT_SCRUB_BITMAP_OPS(csum_error);
@@ -801,7 +803,7 @@ static void scrub_verify_one_sector(struct scrub_stripe *stripe, int sector_nr)
                return;
 
        /* Metadata, verify the full tree block. */
-       if (sector->is_metadata) {
+       if (scrub_bitmap_test_bit_is_metadata(stripe, sector_nr)) {
                /*
                 * Check if the tree block crosses the stripe boundary.  If
                 * crossed the boundary, we cannot verify it but only give a
@@ -850,7 +852,7 @@ static void scrub_verify_one_stripe(struct scrub_stripe *stripe, unsigned long b
 
        for_each_set_bit(sector_nr, &bitmap, stripe->nr_sectors) {
                scrub_verify_one_sector(stripe, sector_nr);
-               if (stripe->sectors[sector_nr].is_metadata)
+               if (scrub_bitmap_test_bit_is_metadata(stripe, sector_nr))
                        sector_nr += sectors_per_tree - 1;
        }
 }
@@ -1019,7 +1021,7 @@ skip:
        for_each_set_bit(sector_nr, &extent_bitmap, stripe->nr_sectors) {
                bool repaired = false;
 
-               if (stripe->sectors[sector_nr].is_metadata) {
+               if (scrub_bitmap_test_bit_is_metadata(stripe, sector_nr)) {
                        nr_meta_sectors++;
                } else {
                        nr_data_sectors++;
@@ -1616,7 +1618,7 @@ static void fill_one_extent_info(struct btrfs_fs_info *fs_info,
 
                scrub_bitmap_set_bit_has_extent(stripe, nr_sector);
                if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
-                       sector->is_metadata = true;
+                       scrub_bitmap_set_bit_is_metadata(stripe, nr_sector);
                        sector->generation = extent_gen;
                }
        }
@@ -1760,7 +1762,6 @@ static void scrub_reset_stripe(struct scrub_stripe *stripe)
        stripe->state = 0;
 
        for (int i = 0; i < stripe->nr_sectors; i++) {
-               stripe->sectors[i].is_metadata = false;
                stripe->sectors[i].csum = NULL;
                stripe->sectors[i].generation = 0;
        }
@@ -1902,7 +1903,7 @@ static bool stripe_has_metadata_error(struct scrub_stripe *stripe)
        int i;
 
        for_each_set_bit(i, &error, stripe->nr_sectors) {
-               if (stripe->sectors[i].is_metadata) {
+               if (scrub_bitmap_test_bit_is_metadata(stripe, i)) {
                        struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
 
                        btrfs_err(fs_info,