tree 7b6cbc6a997e25a7fb6185da7129e539c4ffda8b
parent 8ddf9efe6708f3674f0ddfeb6425fd27bea109a2
author NeilBrown <neilb@cse.unsw.edu.au> 1126308227 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> 1126309150 -0700

[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>