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

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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>
This commit is contained in:
NeilBrown 2005-09-09 16:23:47 -07:00 • committed by Linus Torvalds
parent 8ddf9efe67
commit 4b6d287f62
5 changed files with 165 additions and 16 deletions
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3
include/linux/raid/md_k.h
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@ -275,6 +275,9 @@ struct mddev_s
atomic_t writes_pending;
request_queue_t *queue; /* for plugging ... */
atomic_t write_behind; /* outstanding async IO */
unsigned int max_write_behind; /* 0 = sync */
struct bitmap *bitmap; /* the bitmap for the device */
struct file *bitmap_file; /* the bitmap file */
long bitmap_offset; /* offset from superblock of