btrfs: raid56: avoid double for loop inside raid56_rmw_stripe()

This function doesn't even utilize full stripe skip, just iterate all
the data sectors is definitely enough.

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/raid56.c b/fs/btrfs/raid56.c
index 41cdeff63a6b784e407e494e1c3e3ea7e8e65a17..7ddcac96e844dfac5e9cec29e2932a0626b723c7 100644 (file)
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -1547,9 +1547,9 @@ static int raid56_rmw_stripe(struct btrfs_raid_bio *rbio)
 {
        int bios_to_read = 0;
        struct bio_list bio_list;
+       const int nr_data_sectors = rbio->stripe_nsectors * rbio->nr_data;
        int ret;
-       int sectornr;
-       int stripe;
+       int total_sector_nr;
        struct bio *bio;
 
        bio_list_init(&bio_list);
@@ -1561,38 +1561,35 @@ static int raid56_rmw_stripe(struct btrfs_raid_bio *rbio)
        index_rbio_pages(rbio);
 
        atomic_set(&rbio->error, 0);
-       /*
-        * build a list of bios to read all the missing parts of this
-        * stripe
-        */
-       for (stripe = 0; stripe < rbio->nr_data; stripe++) {
-               for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
-                       struct sector_ptr *sector;
+       /* Build a list of bios to read all the missing data sectors. */
+       for (total_sector_nr = 0; total_sector_nr < nr_data_sectors;
+            total_sector_nr++) {
+               struct sector_ptr *sector;
+               int stripe = total_sector_nr / rbio->stripe_nsectors;
+               int sectornr = total_sector_nr % rbio->stripe_nsectors;
 
-                       /*
-                        * We want to find all the sectors missing from the
-                        * rbio and read them from the disk.  If * sector_in_rbio()
-                        * finds a page in the bio list we don't need to read
-                        * it off the stripe.
-                        */
-                       sector = sector_in_rbio(rbio, stripe, sectornr, 1);
-                       if (sector)
-                               continue;
+               /*
+                * We want to find all the sectors missing from the rbio and
+                * read them from the disk.  If sector_in_rbio() finds a page
+                * in the bio list we don't need to read it off the stripe.
+                */
+               sector = sector_in_rbio(rbio, stripe, sectornr, 1);
+               if (sector)
+                       continue;
 
-                       sector = rbio_stripe_sector(rbio, stripe, sectornr);
-                       /*
-                        * The bio cache may have handed us an uptodate page.
-                        * If so, be happy and use it.
-                        */
-                       if (sector->uptodate)
-                               continue;
+               sector = rbio_stripe_sector(rbio, stripe, sectornr);
+               /*
+                * The bio cache may have handed us an uptodate page.  If so,
+                * use it.
+                */
+               if (sector->uptodate)
+                       continue;
 
-                       ret = rbio_add_io_sector(rbio, &bio_list, sector,
-                                      stripe, sectornr, rbio->stripe_len,
-                                      REQ_OP_READ);
-                       if (ret)
-                               goto cleanup;
-               }
+               ret = rbio_add_io_sector(rbio, &bio_list, sector,
+                              stripe, sectornr, rbio->stripe_len,
+                              REQ_OP_READ);
+               if (ret)
+                       goto cleanup;
        }
 
        bios_to_read = bio_list_size(&bio_list);