[PATCH] md: add write-behind support for md/raid1

If a device is flagged 'WriteMostly' and the array has a bitmap, and the
bitmap superblock indicates that write_behind is allowed, then write_behind is
enabled for WriteMostly devices.

Write requests will be acknowledges as complete to the caller (via b_end_io)
when all non-WriteMostly devices have completed the write, but will not be
cleared from the bitmap until all devices complete.

This requires memory allocation to make a local copy of the data being
written.  If there is insufficient memory, then we fall-back on normal write
semantics.

Signed-Off-By: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 117 insertions, 7 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 28839a8193f2..ba7f5f256161 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -222,8 +222,17 @@ static void raid_end_bio_io(r1bio_t *r1_bio)
 {
         struct bio *bio = r1_bio->master_bio;
 
-        bio_endio(bio, bio->bi_size,
-                test_bit(R1BIO_Uptodate, &r1_bio->state) ? 0 : -EIO);
+        /* if nobody has done the final endio yet, do it now */
+        if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
+                PRINTK(KERN_DEBUG "raid1: sync end %s on sectors %llu-%llu\n",
+                        (bio_data_dir(bio) == WRITE) ? "write" : "read",
+                        (unsigned long long) bio->bi_sector,
+                        (unsigned long long) bio->bi_sector +
+                                (bio->bi_size >> 9) - 1);
+
+                bio_endio(bio, bio->bi_size,
+                        test_bit(R1BIO_Uptodate, &r1_bio->state) ? 0 : -EIO);
+        }
         free_r1bio(r1_bio);
 }
 
@@ -292,7 +301,7 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 {
         int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
         r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
-        int mirror;
+        int mirror, behind;
         conf_t *conf = mddev_to_conf(r1_bio->mddev);
 
         if (bio->bi_size)
@@ -323,16 +332,46 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 
         update_head_pos(mirror, r1_bio);
 
+        behind = test_bit(R1BIO_BehindIO, &r1_bio->state);
+        if (behind) {
+                if (test_bit(WriteMostly, &conf->mirrors[mirror].rdev->flags))
+                        atomic_dec(&r1_bio->behind_remaining);
+
+                /* In behind mode, we ACK the master bio once the I/O has safely
+                 * reached all non-writemostly disks. Setting the Returned bit
+                 * ensures that this gets done only once -- we don't ever want to
+                 * return -EIO here, instead we'll wait */
+
+                if (atomic_read(&r1_bio->behind_remaining) >= (atomic_read(&r1_bio->remaining)-1) &&
+                    test_bit(R1BIO_Uptodate, &r1_bio->state)) {
+                        /* Maybe we can return now */
+                        if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
+                                struct bio *mbio = r1_bio->master_bio;
+                                PRINTK(KERN_DEBUG "raid1: behind end write sectors %llu-%llu\n",
+                                       (unsigned long long) mbio->bi_sector,
+                                       (unsigned long long) mbio->bi_sector +
+                                       (mbio->bi_size >> 9) - 1);
+                                bio_endio(mbio, mbio->bi_size, 0);
+                        }
+                }
+        }
         /*
          *
          * Let's see if all mirrored write operations have finished
          * already.
          */
         if (atomic_dec_and_test(&r1_bio->remaining)) {
+                if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
+                        /* free extra copy of the data pages */
+                        int i = bio->bi_vcnt;
+                        while (i--)
+                                __free_page(bio->bi_io_vec[i].bv_page);
+                }
                 /* clear the bitmap if all writes complete successfully */
                 bitmap_endwrite(r1_bio->mddev->bitmap, r1_bio->sector,
                                 r1_bio->sectors,
-                                !test_bit(R1BIO_Degraded, &r1_bio->state));
+                                !test_bit(R1BIO_Degraded, &r1_bio->state),
+                                behind);
                 md_write_end(r1_bio->mddev);
                 raid_end_bio_io(r1_bio);
         }
@@ -562,6 +601,39 @@ static void device_barrier(conf_t *conf, sector_t sect)
         spin_unlock_irq(&conf->resync_lock);
 }
 
+/* duplicate the data pages for behind I/O */
+static struct page **alloc_behind_pages(struct bio *bio)
+{
+        int i;
+        struct bio_vec *bvec;
+        struct page **pages = kmalloc(bio->bi_vcnt * sizeof(struct page *),
+                                        GFP_NOIO);
+        if (unlikely(!pages))
+                goto do_sync_io;
+
+        memset(pages, 0, bio->bi_vcnt * sizeof(struct page *));
+
+        bio_for_each_segment(bvec, bio, i) {
+                pages[i] = alloc_page(GFP_NOIO);
+                if (unlikely(!pages[i]))
+                        goto do_sync_io;
+                memcpy(kmap(pages[i]) + bvec->bv_offset,
+                        kmap(bvec->bv_page) + bvec->bv_offset, bvec->bv_len);
+                kunmap(pages[i]);
+                kunmap(bvec->bv_page);
+        }
+
+        return pages;
+
+do_sync_io:
+        if (pages)
+                for (i = 0; i < bio->bi_vcnt && pages[i]; i++)
+                        __free_page(pages[i]);
+        kfree(pages);
+        PRINTK("%dB behind alloc failed, doing sync I/O\n", bio->bi_size);
+        return NULL;
+}
+
 static int make_request(request_queue_t *q, struct bio * bio)
 {
         mddev_t *mddev = q->queuedata;
@@ -574,6 +646,7 @@ static int make_request(request_queue_t *q, struct bio * bio)
         struct bitmap *bitmap = mddev->bitmap;
         unsigned long flags;
         struct bio_list bl;
+        struct page **behind_pages = NULL;
 
         if (unlikely(bio_barrier(bio))) {
                 bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
@@ -613,8 +686,6 @@ static int make_request(request_queue_t *q, struct bio * bio)
         r1_bio->mddev = mddev;
         r1_bio->sector = bio->bi_sector;
 
-        r1_bio->state = 0;
-
         if (bio_data_dir(bio) == READ) {
                 /*
                  * read balancing logic:
@@ -675,13 +746,22 @@ static int make_request(request_queue_t *q, struct bio * bio)
         }
         rcu_read_unlock();
 
+        BUG_ON(targets == 0); /* we never fail the last device */
+
         if (targets < conf->raid_disks) {
                 /* array is degraded, we will not clear the bitmap
                  * on I/O completion (see raid1_end_write_request) */
                 set_bit(R1BIO_Degraded, &r1_bio->state);
         }
 
+        /* do behind I/O ? */
+        if (bitmap &&
+            atomic_read(&bitmap->behind_writes) < bitmap->max_write_behind &&
+            (behind_pages = alloc_behind_pages(bio)) != NULL)
+                set_bit(R1BIO_BehindIO, &r1_bio->state);
+
         atomic_set(&r1_bio->remaining, 0);
+        atomic_set(&r1_bio->behind_remaining, 0);
 
         bio_list_init(&bl);
         for (i = 0; i < disks; i++) {
@@ -698,12 +778,31 @@ static int make_request(request_queue_t *q, struct bio * bio)
                 mbio->bi_rw = WRITE;
                 mbio->bi_private = r1_bio;
 
+                if (behind_pages) {
+                        struct bio_vec *bvec;
+                        int j;
+
+                        /* Yes, I really want the '__' version so that
+                         * we clear any unused pointer in the io_vec, rather
+                         * than leave them unchanged.  This is important
+                         * because when we come to free the pages, we won't
+                         * know the originial bi_idx, so we just free
+                         * them all
+                         */
+                        __bio_for_each_segment(bvec, mbio, j, 0)
+                                bvec->bv_page = behind_pages[j];
+                        if (test_bit(WriteMostly, &conf->mirrors[i].rdev->flags))
+                                atomic_inc(&r1_bio->behind_remaining);
+                }
+
                 atomic_inc(&r1_bio->remaining);
 
                 bio_list_add(&bl, mbio);
         }
+        kfree(behind_pages); /* the behind pages are attached to the bios now */
 
-        bitmap_startwrite(bitmap, bio->bi_sector, r1_bio->sectors);
+        bitmap_startwrite(bitmap, bio->bi_sector, r1_bio->sectors,
+                                test_bit(R1BIO_BehindIO, &r1_bio->state));
         spin_lock_irqsave(&conf->device_lock, flags);
         bio_list_merge(&conf->pending_bio_list, &bl);
         bio_list_init(&bl);
@@ -1471,6 +1570,17 @@ out:
 static int stop(mddev_t *mddev)
 {
         conf_t *conf = mddev_to_conf(mddev);
+        struct bitmap *bitmap = mddev->bitmap;
+        int behind_wait = 0;
+
+        /* wait for behind writes to complete */
+        while (bitmap && atomic_read(&bitmap->behind_writes) > 0) {
+                behind_wait++;
+                printk(KERN_INFO "raid1: behind writes in progress on device %s, waiting to stop (%d)\n", mdname(mddev), behind_wait);
+                set_current_state(TASK_UNINTERRUPTIBLE);
+                schedule_timeout(HZ); /* wait a second */
+                /* need to kick something here to make sure I/O goes? */
+        }
 
         md_unregister_thread(mddev->thread);
         mddev->thread = NULL;