md/raid5 revise rules for when to update metadata during reshape

[safe/jmp/linux-2.6] / drivers / md / raid5.c

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bb4b12e..3bbc6d6 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3766,7 +3766,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
        int new_data_disks = conf->raid_disks - conf->max_degraded;
        int i;
        int dd_idx;
-       sector_t writepos, safepos, gap;
+       sector_t writepos, readpos, safepos;
        sector_t stripe_addr;
        int reshape_sectors;
        struct list_head stripes;
@@ -3806,26 +3806,46 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
         */
        writepos = conf->reshape_progress;
        sector_div(writepos, new_data_disks);
+       readpos = conf->reshape_progress;
+       sector_div(readpos, data_disks);
        safepos = conf->reshape_safe;
        sector_div(safepos, data_disks);
        if (mddev->delta_disks < 0) {
                writepos -= reshape_sectors;
+               readpos += reshape_sectors;
                safepos += reshape_sectors;
-               gap = conf->reshape_safe - conf->reshape_progress;
        } else {
                writepos += reshape_sectors;
+               readpos -= reshape_sectors;
                safepos -= reshape_sectors;
-               gap = conf->reshape_progress - conf->reshape_safe;
        }
 
+       /* 'writepos' is the most advanced device address we might write.
+        * 'readpos' is the least advanced device address we might read.
+        * 'safepos' is the least address recorded in the metadata as having
+        *     been reshaped.
+        * If 'readpos' is behind 'writepos', then there is no way that we can
+        * ensure safety in the face of a crash - that must be done by userspace
+        * making a backup of the data.  So in that case there is no particular
+        * rush to update metadata.
+        * Otherwise if 'safepos' is behind 'writepos', then we really need to
+        * update the metadata to advance 'safepos' to match 'readpos' so that
+        * we can be safe in the event of a crash.
+        * So we insist on updating metadata if safepos is behind writepos and
+        * readpos is beyond writepos.
+        * In any case, update the metadata every 10 seconds.
+        * Maybe that number should be configurable, but I'm not sure it is
+        * worth it.... maybe it could be a multiple of safemode_delay???
+        */
        if ((mddev->delta_disks < 0
-            ? writepos < safepos
-            : writepos > safepos) ||
-           gap > (new_data_disks)*3000*2 /*3Meg*/) {
+            ? (safepos > writepos && readpos < writepos)
+            : (safepos < writepos && readpos > writepos)) ||
+           time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
                /* Cannot proceed until we've updated the superblock... */
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes)==0);
                mddev->reshape_position = conf->reshape_progress;
+               conf->reshape_checkpoint = jiffies;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait, mddev->flags == 0 ||
@@ -3923,6 +3943,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
                wait_event(conf->wait_for_overlap,
                           atomic_read(&conf->reshape_stripes) == 0);
                mddev->reshape_position = conf->reshape_progress;
+               conf->reshape_checkpoint = jiffies;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait,
@@ -4957,6 +4978,7 @@ static int raid5_start_reshape(mddev_t *mddev)
                spin_unlock_irq(&conf->device_lock);
                return -EAGAIN;
        }
+       conf->reshape_checkpoint = jiffies;
        md_wakeup_thread(mddev->sync_thread);
        md_new_event(mddev);
        return 0;