[PATCH] md: optimised resync using Bitmap based intent logging

With this patch, the intent to write to some block in the array can be logged
to a bitmap file.  Each bit represents some number of sectors and is set
before any update happens, and only cleared when all writes relating to all
sectors are complete.

After an unclean shutdown, information in this bitmap can be used to optimise
resync - only sectors which could be out-of-sync need to be updated.

Also if a drive is removed and then added back into an array, the recovery can
make use of the bitmap to optimise reconstruction.  This is not implemented in
this patch.

Currently the bitmap is stored in a file which must (obviously) be stored on a
separate device.

The patch only provided infrastructure.  It does not update any personalities
to bitmap intent logging.

Md arrays can still be used with no bitmap file.  This patch has minimal
impact on such arrays.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index bce0032decff..16e94a9f0f8c 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -267,6 +267,9 @@ struct mddev_s
         atomic_t                        writes_pending; 
         request_queue_t                 *queue; /* for plugging ... */
 
+        struct bitmap                   *bitmap; /* the bitmap for the device */
+        struct file                     *bitmap_file; /* the bitmap file */
+
         struct list_head                all_mddevs;
 };
 
@@ -341,6 +344,7 @@ typedef struct mdk_thread_s {
         unsigned long           flags;
         struct completion       *event;
         struct task_struct      *tsk;
+        unsigned long           timeout;
         const char              *name;
 } mdk_thread_t;