[PATCH] md: add write-behind support for md/raid1

If a device is flagged 'WriteMostly' and the array has a bitmap, and the
bitmap superblock indicates that write_behind is allowed, then write_behind is
enabled for WriteMostly devices.

Write requests will be acknowledges as complete to the caller (via b_end_io)
when all non-WriteMostly devices have completed the write, but will not be
cleared from the bitmap until all devices complete.

This requires memory allocation to make a local copy of the data being
written.  If there is insufficient memory, then we fall-back on normal write
semantics.

Signed-Off-By: Paul Clements <paul.clements@steeleye.com>
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, 10 insertions, 5 deletions

diff --git a/include/linux/raid/bitmap.h b/include/linux/raid/bitmap.h
index 4bf1659f8aa8..9de99198caf1 100644
--- a/include/linux/raid/bitmap.h
+++ b/include/linux/raid/bitmap.h
@@ -7,7 +7,7 @@
 #define BITMAP_H 1
 
 #define BITMAP_MAJOR 3
-#define BITMAP_MINOR 38
+#define BITMAP_MINOR 39
 
 /*
  * in-memory bitmap:
@@ -147,8 +147,9 @@ typedef struct bitmap_super_s {
         __u32 state;        /* 48  bitmap state information */
         __u32 chunksize;    /* 52  the bitmap chunk size in bytes */
         __u32 daemon_sleep; /* 56  seconds between disk flushes */
+        __u32 write_behind; /* 60  number of outstanding write-behind writes */
 
-        __u8  pad[256 - 60]; /* set to zero */
+        __u8  pad[256 - 64]; /* set to zero */
 } bitmap_super_t;
 
 /* notes:
@@ -226,6 +227,9 @@ struct bitmap {
 
         unsigned long flags;
 
+        unsigned long max_write_behind; /* write-behind mode */
+        atomic_t behind_writes;
+
         /*
          * the bitmap daemon - periodically wakes up and sweeps the bitmap
          * file, cleaning up bits and flushing out pages to disk as necessary
@@ -260,9 +264,10 @@ int  bitmap_setallbits(struct bitmap *bitmap);
 void bitmap_write_all(struct bitmap *bitmap);
 
 /* these are exported */
-int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors);
-void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors,
-                     int success);
+int bitmap_startwrite(struct bitmap *bitmap, sector_t offset,
+                        unsigned long sectors, int behind);
+void bitmap_endwrite(struct bitmap *bitmap, sector_t offset,
+                        unsigned long sectors, int success, int behind);
 int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int degraded);
 void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int aborted);
 void bitmap_close_sync(struct bitmap *bitmap);