md: add proper merge_bvec handling to RAID0 and Linear.

These personalities currently set a max request size of one page
when any member device has a merge_bvec_fn because they don't
bother to call that function.

This causes extra works in splitting and combining requests.

So make the extra effort to call the merge_bvec_fn when it exists
so that we end up with larger requests out the bottom.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/md/raid0.h b/drivers/md/raid0.h
index 0884bba8df4c..05539d9c97f0 100644
--- a/drivers/md/raid0.h
+++ b/drivers/md/raid0.h
@@ -4,13 +4,16 @@
 struct strip_zone {
         sector_t zone_end;      /* Start of the next zone (in sectors) */
         sector_t dev_start;     /* Zone offset in real dev (in sectors) */
-        int nb_dev;             /* # of devices attached to the zone */
+        int      nb_dev;        /* # of devices attached to the zone */
 };
 
 struct r0conf {
-        struct strip_zone *strip_zone;
-        struct md_rdev **devlist; /* lists of rdevs, pointed to by strip_zone->dev */
-        int nr_strip_zones;
+        struct strip_zone       *strip_zone;
+        struct md_rdev          **devlist; /* lists of rdevs, pointed to
+                                            * by strip_zone->dev */
+        int                     nr_strip_zones;
+        int                     has_merge_bvec; /* at least one member has
+                                                 * a merge_bvec_fn */
 };
 
 #endif