[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>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 28839a8..ba7f5f2 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -222,8 +222,17 @@
{
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 @@
{
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 @@
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 @@
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 @@
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 @@
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 @@
}
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 @@
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 @@
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;