btrfs: optimize simple reads in btrfsic_map_block

Pass a smap into __btrfs_map_block so that the usual case of a read that
doesn't require parity raid recovery doesn't need an extra memory
allocation for the btrfs_io_context.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index b440803..fe15367 100644 (file)
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -1459,13 +1459,13 @@ static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
        struct btrfs_fs_info *fs_info = state->fs_info;
        int ret;
        u64 length;
-       struct btrfs_io_context *multi = NULL;
+       struct btrfs_io_context *bioc = NULL;
+       struct btrfs_io_stripe smap, *map;
        struct btrfs_device *device;
 
        length = len;
-       ret = btrfs_map_block(fs_info, BTRFS_MAP_READ,
-                             bytenr, &length, &multi, mirror_num);
-
+       ret = __btrfs_map_block(fs_info, BTRFS_MAP_READ, bytenr, &length, &bioc,
+                               NULL, &mirror_num, 0);
        if (ret) {
                block_ctx_out->start = 0;
                block_ctx_out->dev_bytenr = 0;
@@ -1478,21 +1478,26 @@ static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
                return ret;
        }
 
-       device = multi->stripes[0].dev;
+       if (bioc)
+               map = &bioc->stripes[0];
+       else
+               map = &smap;
+
+       device = map->dev;
        if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state) ||
            !device->bdev || !device->name)
                block_ctx_out->dev = NULL;
        else
                block_ctx_out->dev = btrfsic_dev_state_lookup(
                                                        device->bdev->bd_dev);
-       block_ctx_out->dev_bytenr = multi->stripes[0].physical;
+       block_ctx_out->dev_bytenr = map->physical;
        block_ctx_out->start = bytenr;
        block_ctx_out->len = len;
        block_ctx_out->datav = NULL;
        block_ctx_out->pagev = NULL;
        block_ctx_out->mem_to_free = NULL;
 
-       kfree(multi);
+       kfree(bioc);
        if (NULL == block_ctx_out->dev) {
                ret = -ENXIO;
                pr_info("btrfsic: error, cannot lookup dev (#1)!\n");