diff options
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/md/raid5.c | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 6ba39408212..56303ff3173 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -18,6 +18,30 @@ * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ +/* + * BITMAP UNPLUGGING: + * + * The sequencing for updating the bitmap reliably is a little + * subtle (and I got it wrong the first time) so it deserves some + * explanation. + * + * We group bitmap updates into batches. Each batch has a number. + * We may write out several batches at once, but that isn't very important. + * conf->bm_write is the number of the last batch successfully written. + * conf->bm_flush is the number of the last batch that was closed to + * new additions. + * When we discover that we will need to write to any block in a stripe + * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq + * the number of the batch it will be in. This is bm_flush+1. + * When we are ready to do a write, if that batch hasn't been written yet, + * we plug the array and queue the stripe for later. + * When an unplug happens, we increment bm_flush, thus closing the current + * batch. + * When we notice that bm_flush > bm_write, we write out all pending updates + * to the bitmap, and advance bm_write to where bm_flush was. + * This may occasionally write a bit out twice, but is sure never to + * miss any bits. + */ #include <linux/module.h> #include <linux/slab.h> @@ -92,7 +116,7 @@ static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh) list_add_tail(&sh->lru, &conf->delayed_list); blk_plug_device(conf->mddev->queue); } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) && - conf->seq_write == sh->bm_seq) { + sh->bm_seq - conf->seq_write > 0) { list_add_tail(&sh->lru, &conf->bitmap_list); blk_plug_device(conf->mddev->queue); } else { @@ -1273,9 +1297,9 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in (unsigned long long)sh->sector, dd_idx); if (conf->mddev->bitmap && firstwrite) { - sh->bm_seq = conf->seq_write; bitmap_startwrite(conf->mddev->bitmap, sh->sector, STRIPE_SECTORS, 0); + sh->bm_seq = conf->seq_flush+1; set_bit(STRIPE_BIT_DELAY, &sh->state); } @@ -2918,7 +2942,7 @@ static void raid5d (mddev_t *mddev) while (1) { struct list_head *first; - if (conf->seq_flush - conf->seq_write > 0) { + if (conf->seq_flush != conf->seq_write) { int seq = conf->seq_flush; spin_unlock_irq(&conf->device_lock); bitmap_unplug(mddev->bitmap); |