[PATCH] md: Only checkpoint expansion progress occasionally

Instead of checkpointing at each stripe, only checkpoint when a new write
would overwrite uncheckpointed data.  Block any write to the uncheckpointed
area.  Arbitrarily checkpoint at least every 3Meg.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 45 insertions, 11 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 20ae32d67e21..089a32604305 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1762,8 +1762,9 @@ static int make_request(request_queue_t *q, struct bio * bi)
         for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
                 DEFINE_WAIT(w);
                 int disks;
-                
+
         retry:
+                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
                 if (likely(conf->expand_progress == MaxSector))
                         disks = conf->raid_disks;
                 else {
@@ -1771,6 +1772,13 @@ static int make_request(request_queue_t *q, struct bio * bi)
                         disks = conf->raid_disks;
                         if (logical_sector >= conf->expand_progress)
                                 disks = conf->previous_raid_disks;
+                        else {
+                                if (logical_sector >= conf->expand_lo) {
+                                        spin_unlock_irq(&conf->device_lock);
+                                        schedule();
+                                        goto retry;
+                                }
+                        }
                         spin_unlock_irq(&conf->device_lock);
                 }
                 new_sector = raid5_compute_sector(logical_sector, disks, disks - 1,
@@ -1779,7 +1787,6 @@ static int make_request(request_queue_t *q, struct bio * bi)
                         (unsigned long long)new_sector, 
                         (unsigned long long)logical_sector);
 
-                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
                 sh = get_active_stripe(conf, new_sector, disks, pd_idx, (bi->bi_rw&RWA_MASK));
                 if (sh) {
                         if (unlikely(conf->expand_progress != MaxSector)) {
@@ -1877,6 +1884,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                  */
                 int i;
                 int dd_idx;
+                sector_t writepos, safepos, gap;
 
                 if (sector_nr == 0 &&
                     conf->expand_progress != 0) {
@@ -1887,15 +1895,36 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                         return sector_nr;
                 }
 
-                /* Cannot proceed until we've updated the superblock... */
-                wait_event(conf->wait_for_overlap,
-                           atomic_read(&conf->reshape_stripes)==0);
-                mddev->reshape_position = conf->expand_progress;
-
-                mddev->sb_dirty = 1;
-                md_wakeup_thread(mddev->thread);
-                wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
-                        kthread_should_stop());
+                /* we update the metadata when there is more than 3Meg
+                 * in the block range (that is rather arbitrary, should
+                 * probably be time based) or when the data about to be
+                 * copied would over-write the source of the data at
+                 * the front of the range.
+                 * i.e. one new_stripe forward from expand_progress new_maps
+                 * to after where expand_lo old_maps to
+                 */
+                writepos = conf->expand_progress +
+                        conf->chunk_size/512*(conf->raid_disks-1);
+                sector_div(writepos, conf->raid_disks-1);
+                safepos = conf->expand_lo;
+                sector_div(safepos, conf->previous_raid_disks-1);
+                gap = conf->expand_progress - conf->expand_lo;
+
+                if (writepos >= safepos ||
+                    gap > (conf->raid_disks-1)*3000*2 /*3Meg*/) {
+                        /* Cannot proceed until we've updated the superblock... */
+                        wait_event(conf->wait_for_overlap,
+                                   atomic_read(&conf->reshape_stripes)==0);
+                        mddev->reshape_position = conf->expand_progress;
+                        mddev->sb_dirty = 1;
+                        md_wakeup_thread(mddev->thread);
+                        wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
+                                   kthread_should_stop());
+                        spin_lock_irq(&conf->device_lock);
+                        conf->expand_lo = mddev->reshape_position;
+                        spin_unlock_irq(&conf->device_lock);
+                        wake_up(&conf->wait_for_overlap);
+                }
 
                 for (i=0; i < conf->chunk_size/512; i+= STRIPE_SECTORS) {
                         int j;
@@ -2322,6 +2351,7 @@ static int run(mddev_t *mddev)
 
         if (conf->expand_progress != MaxSector) {
                 printk("...ok start reshape thread\n");
+                conf->expand_lo = conf->expand_progress;
                 atomic_set(&conf->reshape_stripes, 0);
                 clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
                 clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
@@ -2610,6 +2640,7 @@ static int raid5_reshape(mddev_t *mddev, int raid_disks)
         conf->previous_raid_disks = conf->raid_disks;
         conf->raid_disks = raid_disks;
         conf->expand_progress = 0;
+        conf->expand_lo = 0;
         spin_unlock_irq(&conf->device_lock);
 
         /* Add some new drives, as many as will fit.
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index abcdf0d0658a..914af667044f 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -217,6 +217,9 @@ struct raid5_private_data {
 
         /* used during an expand */
         sector_t                expand_progress;        /* MaxSector when no expand happening */
+        sector_t                expand_lo; /* from here up to expand_progress it out-of-bounds
+                                            * as we haven't flushed the metadata yet
+                                            */
         int                     previous_raid_disks;
 
         struct list_head        handle_list; /* stripes needing handling */