btrfs: add fast path for single device io in __btrfs_map_block

There is no need for most of the btrfs_io_context when doing I/O to a
single device.  To support such I/O without the extra btrfs_io_context
allocation, turn the mirror_num argument into a pointer so that it can
be used to output the selected mirror number, and add an optional
argument that points to a btrfs_io_stripe structure, which will be
filled with a single extent if provided by the caller.

In that case the btrfs_io_context allocation can be skipped as all
information for the single device I/O is provided in the mirror_num
argument and the on-stack btrfs_io_stripe.  A caller that makes use of
this new argument will be added in the next commit.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Tested-by: Nikolay Borisov <nborisov@suse.com>
Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 67c3aa8..58c9993 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -249,10 +249,10 @@ static int init_first_rw_device(struct btrfs_trans_handle *trans);
 static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info);
 static void btrfs_dev_stat_print_on_load(struct btrfs_device *device);
 static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
-                            enum btrfs_map_op op,
-                            u64 logical, u64 *length,
+                            enum btrfs_map_op op, u64 logical, u64 *length,
                             struct btrfs_io_context **bioc_ret,
-                            int mirror_num, int need_raid_map);
+                            struct btrfs_io_stripe *smap,
+                            int *mirror_num_ret, int need_raid_map);
 
 /*
  * Device locking
@@ -6093,7 +6093,7 @@ static int get_extra_mirror_from_replace(struct btrfs_fs_info *fs_info,
        int ret = 0;
 
        ret = __btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
-                               logical, &length, &bioc, 0, 0);
+                               logical, &length, &bioc, NULL, NULL, 0);
        if (ret) {
                ASSERT(bioc == NULL);
                return ret;
@@ -6350,11 +6350,19 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, struct extent_map *em,
        return 0;
 }
 
+static void set_io_stripe(struct btrfs_io_stripe *dst, const struct map_lookup *map,
+                         u32 stripe_index, u64 stripe_offset, u64 stripe_nr)
+{
+       dst->dev = map->stripes[stripe_index].dev;
+       dst->physical = map->stripes[stripe_index].physical +
+                       stripe_offset + stripe_nr * map->stripe_len;
+}
+
 static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
-                            enum btrfs_map_op op,
-                            u64 logical, u64 *length,
+                            enum btrfs_map_op op, u64 logical, u64 *length,
                             struct btrfs_io_context **bioc_ret,
-                            int mirror_num, int need_raid_map)
+                            struct btrfs_io_stripe *smap,
+                            int *mirror_num_ret, int need_raid_map)
 {
        struct extent_map *em;
        struct map_lookup *map;
@@ -6365,6 +6373,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
        int data_stripes;
        int i;
        int ret = 0;
+       int mirror_num = (mirror_num_ret ? *mirror_num_ret : 0);
        int num_stripes;
        int max_errors = 0;
        int tgtdev_indexes = 0;
@@ -6525,6 +6534,29 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
                tgtdev_indexes = num_stripes;
        }
 
+       /*
+        * If this I/O maps to a single device, try to return the device and
+        * physical block information on the stack instead of allocating an
+        * I/O context structure.
+        */
+       if (smap && num_alloc_stripes == 1 &&
+           !((map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) && mirror_num > 1) &&
+           (!need_full_stripe(op) || !dev_replace_is_ongoing ||
+            !dev_replace->tgtdev)) {
+               if (patch_the_first_stripe_for_dev_replace) {
+                       smap->dev = dev_replace->tgtdev;
+                       smap->physical = physical_to_patch_in_first_stripe;
+                       *mirror_num_ret = map->num_stripes + 1;
+               } else {
+                       set_io_stripe(smap, map, stripe_index, stripe_offset,
+                                     stripe_nr);
+                       *mirror_num_ret = mirror_num;
+               }
+               *bioc_ret = NULL;
+               ret = 0;
+               goto out;
+       }
+
        bioc = alloc_btrfs_io_context(fs_info, num_alloc_stripes, tgtdev_indexes);
        if (!bioc) {
                ret = -ENOMEM;
@@ -6532,9 +6564,8 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
        }
 
        for (i = 0; i < num_stripes; i++) {
-               bioc->stripes[i].physical = map->stripes[stripe_index].physical +
-                       stripe_offset + stripe_nr * map->stripe_len;
-               bioc->stripes[i].dev = map->stripes[stripe_index].dev;
+               set_io_stripe(&bioc->stripes[i], map, stripe_index, stripe_offset,
+                             stripe_nr);
                stripe_index++;
        }
 
@@ -6602,7 +6633,7 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
                      struct btrfs_io_context **bioc_ret, int mirror_num)
 {
        return __btrfs_map_block(fs_info, op, logical, length, bioc_ret,
-                                mirror_num, 0);
+                                NULL, &mirror_num, 0);
 }
 
 /* For Scrub/replace */
@@ -6610,7 +6641,8 @@ int btrfs_map_sblock(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
                     u64 logical, u64 *length,
                     struct btrfs_io_context **bioc_ret)
 {
-       return __btrfs_map_block(fs_info, op, logical, length, bioc_ret, 0, 1);
+       return __btrfs_map_block(fs_info, op, logical, length, bioc_ret,
+                                NULL, NULL, 1);
 }
 
 /*
@@ -6820,8 +6852,8 @@ void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror
        struct btrfs_io_context *bioc = NULL;
 
        btrfs_bio_counter_inc_blocked(fs_info);
-       ret = __btrfs_map_block(fs_info, btrfs_op(bio), logical,
-                               &map_length, &bioc, mirror_num, 1);
+       ret = __btrfs_map_block(fs_info, btrfs_op(bio), logical, &map_length,
+                               &bioc, NULL, &mirror_num, 1);
        if (ret) {
                btrfs_bio_counter_dec(fs_info);
                btrfs_bio_end_io(btrfs_bio(bio), errno_to_blk_status(ret));