lkml.org 
[lkml]   [2008]   [May]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    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);
    }

    \
     
     \ /
      Last update: 2008-05-19 03:15    [W:0.021 / U:63.100 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site