[PATCHSET] block: reimplement FLUSH/FUA to support merge

[Tejun Heo]

Hello,

This patchset reimplements (yeah, once more) so that FLUSH/FUA
requests can be merged.  This is inspired by Darrick's patches to
merge multiple zero-data flushes which helps workloads with highly
concurrent fsync requests.

For more information, please read the patch description on the third
patch.

 0001-block-add-REQ_FLUSH_SEQ.patch
 0002-block-improve-flush-bio-completion.patch
 0003-block-reimplement-FLUSH-FUA-to-support-merge.patch

0001-0002 prepare for the reimplementation.  0003 reimplements.

Tested on FLUSH+FUA, FLUSH, and no FLUSH configurations.  Works pretty
solid for me.  Darrick says that preliminary performance test looks
okay.  Darrick, please use this version for further testing as I fixed
a few problems.

This patchset is based on 2.6.38-rc1 (2b1caf6e) and available in the
following git branch,

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git block-flush-merge

and contains the following changes.

 block/blk-core.c          |   56 ++---
 block/blk-flush.c         |  441 +++++++++++++++++++++++++++++++---------------
 block/blk.h               |   12 -
 block/elevator.c          |    7 
 include/linux/blk_types.h |    2 
 include/linux/blkdev.h    |   18 +
 include/linux/elevator.h  |    1 
 7 files changed, 355 insertions(+), 182 deletions(-)

Thanks.

--
tejun
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