md/raid5: allow each slot to have an extra replacement device

Just enhance data structures to record a second device per slot to be
used as a 'replacement' device, replacing the original.
We also have a second bio in each slot in each stripe_head.  This will
only be used when writing to the array - we need to write to both the
original and the replacement at the same time, so will need two bios.

For now, only try using the replacement drive for aligned-reads.
In this case, we prefer the replacement if it has been recovered far
enough, otherwise use the original.

This includes a small enhancement.  Previously we would only do
aligned reads if the target device was fully recovered.  Now we also
do them if it has recovered far enough.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 6b9fc58..94bc35b 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3594,6 +3594,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
        int dd_idx;
        struct bio* align_bi;
        struct md_rdev *rdev;
+       sector_t end_sector;
 
        if (!in_chunk_boundary(mddev, raid_bio)) {
                pr_debug("chunk_aligned_read : non aligned\n");
@@ -3618,9 +3619,19 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
                                                    0,
                                                    &dd_idx, NULL);
 
+       end_sector = align_bi->bi_sector + (align_bi->bi_size >> 9);
        rcu_read_lock();
-       rdev = rcu_dereference(conf->disks[dd_idx].rdev);
-       if (rdev && test_bit(In_sync, &rdev->flags)) {
+       rdev = rcu_dereference(conf->disks[dd_idx].replacement);
+       if (!rdev || test_bit(Faulty, &rdev->flags) ||
+           rdev->recovery_offset < end_sector) {
+               rdev = rcu_dereference(conf->disks[dd_idx].rdev);
+               if (rdev &&
+                   (test_bit(Faulty, &rdev->flags) ||
+                   !(test_bit(In_sync, &rdev->flags) ||
+                     rdev->recovery_offset >= end_sector)))
+                       rdev = NULL;
+       }
+       if (rdev) {
                sector_t first_bad;
                int bad_sectors;
 

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index e10c553..43106f0 100644 (file)
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -226,8 +226,11 @@ struct stripe_head {
                #endif
        } ops;
        struct r5dev {
-               struct bio      req;
-               struct bio_vec  vec;
+               /* rreq and rvec are used for the replacement device when
+                * writing data to both devices.
+                */
+               struct bio      req, rreq;
+               struct bio_vec  vec, rvec;
                struct page     *page;
                struct bio      *toread, *read, *towrite, *written;
                sector_t        sector;                 /* sector of this page */
@@ -252,29 +255,35 @@ struct stripe_head_state {
        int handle_bad_blocks;
 };
 
-/* Flags */
-#define        R5_UPTODATE     0       /* page contains current data */
-#define        R5_LOCKED       1       /* IO has been submitted on "req" */
-#define        R5_OVERWRITE    2       /* towrite covers whole page */
+/* Flags for struct r5dev.flags */
+enum r5dev_flags {
+       R5_UPTODATE,    /* page contains current data */
+       R5_LOCKED,      /* IO has been submitted on "req" */
+       R5_OVERWRITE,   /* towrite covers whole page */
 /* and some that are internal to handle_stripe */
-#define        R5_Insync       3       /* rdev && rdev->in_sync at start */
-#define        R5_Wantread     4       /* want to schedule a read */
-#define        R5_Wantwrite    5
-#define        R5_Overlap      7       /* There is a pending overlapping request on this block */
-#define        R5_ReadError    8       /* seen a read error here recently */
-#define        R5_ReWrite      9       /* have tried to over-write the readerror */
+       R5_Insync,      /* rdev && rdev->in_sync at start */
+       R5_Wantread,    /* want to schedule a read */
+       R5_Wantwrite,
+       R5_Overlap,     /* There is a pending overlapping request
+                        * on this block */
+       R5_ReadError,   /* seen a read error here recently */
+       R5_ReWrite,     /* have tried to over-write the readerror */
 
-#define        R5_Expanded     10      /* This block now has post-expand data */
-#define        R5_Wantcompute  11      /* compute_block in progress treat as
-                                * uptodate
-                                */
-#define        R5_Wantfill     12      /* dev->toread contains a bio that needs
-                                * filling
-                                */
-#define        R5_Wantdrain    13      /* dev->towrite needs to be drained */
-#define        R5_WantFUA      14      /* Write should be FUA */
-#define        R5_WriteError   15      /* got a write error - need to record it */
-#define        R5_MadeGood     16      /* A bad block has been fixed by writing to it*/
+       R5_Expanded,    /* This block now has post-expand data */
+       R5_Wantcompute, /* compute_block in progress treat as
+                        * uptodate
+                        */
+       R5_Wantfill,    /* dev->toread contains a bio that needs
+                        * filling
+                        */
+       R5_Wantdrain,   /* dev->towrite needs to be drained */
+       R5_WantFUA,     /* Write should be FUA */
+       R5_WriteError,  /* got a write error - need to record it */
+       R5_MadeGood,    /* A bad block has been fixed by writing to it */
+       R5_ReadRepl,    /* Will/did read from replacement rather than orig */
+       R5_MadeGoodRepl,/* A bad block on the replacement device has been
+                        * fixed by writing to it */
+};
 /*
  * Write method
  */
@@ -344,7 +353,7 @@ enum {
 
 
 struct disk_info {
-       struct md_rdev  *rdev;
+       struct md_rdev  *rdev, *replacement;
 };
 
 struct r5conf {