Messages in this thread Patch in this message | | | From | NeilBrown <> | Date | Mon, 19 May 2008 11:10:57 +1000 | Subject | [PATCH 008 of 10] md: Improve setting of "events_cleared" for write-intent bitmaps. |
| |
When an array is degraded, bits in the write-intent bitmap are not cleared, so that if the missing device is re-added, it can be synced by only updated those parts of the device that have changed since it was removed.
The enable this a 'events_cleared' value is stored. It is the event counter for the array the last time that any bits were cleared.
Sometime - if a device disappears from an array while it is 'clean' - the events_cleared value gets updated incorrectly (there are subtle ordering issues between updateing events in the main metadata and the bitmap metadata) resulting in the missing device appearing to require a full resync when it is re-added.
With this patch, we update events_cleared precised when we are about to clear a bit in the bitmap. This makes it more "obviously correct". We also need to update events_cleared when the event_count is going backwards (as happens on a dirty->clean transition of a non-degraded array).
Thanks to Mike Snitzer for identifying this problem and testing early "fixes".
Cc: "Mike Snitzer" <snitzer@gmail.com> Signed-off-by: Neil Brown <neilb@suse.de>
### Diffstat output ./drivers/md/bitmap.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)
diff .prev/drivers/md/bitmap.c ./drivers/md/bitmap.c --- .prev/drivers/md/bitmap.c 2008-05-19 11:02:35.000000000 +1000 +++ ./drivers/md/bitmap.c 2008-05-19 11:04:00.000000000 +1000 @@ -454,8 +454,11 @@ void bitmap_update_sb(struct bitmap *bit spin_unlock_irqrestore(&bitmap->lock, flags); sb = (bitmap_super_t *)kmap_atomic(bitmap->sb_page, KM_USER0); sb->events = cpu_to_le64(bitmap->mddev->events); - if (!bitmap->mddev->degraded) - sb->events_cleared = cpu_to_le64(bitmap->mddev->events); + if (bitmap->mddev->events < bitmap->events_cleared) { + /* rocking back to read-only */ + bitmap->events_cleared = bitmap->mddev->events; + sb->events_cleared = cpu_to_le64(bitmap->events_cleared); + } kunmap_atomic(sb, KM_USER0); write_page(bitmap, bitmap->sb_page, 1); } @@ -1085,9 +1088,22 @@ void bitmap_daemon_work(struct bitmap *b } else spin_unlock_irqrestore(&bitmap->lock, flags); lastpage = page; -/* - printk("bitmap clean at page %lu\n", j); -*/ + + /* We are possibly going to clear some bits, so make + * sure that events_cleared is up-to-date. + */ + if (bitmap->events_cleared < bitmap->mddev->events) { + bitmap_super_t *sb; + bitmap->events_cleared = bitmap->mddev->events; + wait_event(bitmap->mddev->sb_wait, + !test_bit(MD_CHANGE_CLEAN, + &bitmap->mddev->flags)); + sb = kmap_atomic(bitmap->sb_page, KM_USER0); + sb->events_cleared = + cpu_to_le64(bitmap->events_cleared); + kunmap_atomic(sb, KM_USER0); + write_page(bitmap, bitmap->sb_page, 1); + } spin_lock_irqsave(&bitmap->lock, flags); clear_page_attr(bitmap, page, BITMAP_PAGE_CLEAN); }
| |