raid5: Add R5_ReadNoMerge flag which prevent bio from merging at block layer

Because bios will merge at block-layer,so bios-error may caused by other
bio which be merged into to the same request.
Using this flag,it will find exactly error-sector and not do redundant
operation like re-write and re-read.

V0->V1:Using REQ_FLUSH instead REQ_NOMERGE avoid bio merging at block
layer.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 13 insertions, 2 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c2192a2907e4..29493982dbf5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -653,6 +653,9 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
                         else
                                 bi->bi_sector = (sh->sector
                                                  + rdev->data_offset);
+                        if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
+                                bi->bi_rw |= REQ_FLUSH;
+
                         bi->bi_flags = 1 << BIO_UPTODATE;
                         bi->bi_idx = 0;
                         bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
@@ -1750,7 +1753,9 @@ static void raid5_end_read_request(struct bio * bi, int error)
                         atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
                         clear_bit(R5_ReadError, &sh->dev[i].flags);
                         clear_bit(R5_ReWrite, &sh->dev[i].flags);
-                }
+                } else if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
+                        clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
+
                 if (atomic_read(&rdev->read_errors))
                         atomic_set(&rdev->read_errors, 0);
         } else {
@@ -1795,7 +1800,11 @@ static void raid5_end_read_request(struct bio * bi, int error)
                 else
                         retry = 1;
                 if (retry)
-                        set_bit(R5_ReadError, &sh->dev[i].flags);
+                        if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) {
+                                set_bit(R5_ReadError, &sh->dev[i].flags);
+                                clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
+                        } else
+                                set_bit(R5_ReadNoMerge, &sh->dev[i].flags);
                 else {
                         clear_bit(R5_ReadError, &sh->dev[i].flags);
                         clear_bit(R5_ReWrite, &sh->dev[i].flags);
@@ -4515,6 +4524,7 @@ static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
                         return handled;
                 }
 
+                set_bit(R5_ReadNoMerge, &sh->dev[dd_idx].flags);
                 handle_stripe(sh);
                 release_stripe(sh);
                 handled++;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index f03fb3395183..61dbb615c30b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -274,6 +274,7 @@ enum r5dev_flags {
         R5_Wantwrite,
         R5_Overlap,     /* There is a pending overlapping request
                          * on this block */
+        R5_ReadNoMerge, /* prevent bio from merging in block-layer */
         R5_ReadError,   /* seen a read error here recently */
         R5_ReWrite,     /* have tried to over-write the readerror */