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Subject[PATCH v2 0/5] blk-mq: abstract tag allocation out into scale_bitmap library
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From: Omar Sandoval <osandov@fb.com>

Here's v2 of the patch making blk-mq's scalable bitmaps a generic
library, now blown up into 5 patches. v1 is here [1].

Changes since v1:

- Return -EINVAL instead of BUG_ON() if an invalid shift is passed to
the initialization functions.
- Rename last_cache to alloc_hint.
- Split the wait queue allocation change into a separate patch. Patch 1
should now be a no-op.
- Add patches 3 and 4 to make the API cleaner by pushing some context
from the blk-mq data structures into the common scale_bitmap code.
- Add patch 5 to randomize the allocation hint on initialization like
was intended originally for blk-mq.

I ran some fio jobs on top of null-blk and verified that there was no
performance impact from patches 1-4. Patch 5 is a slight win, although I
couldn't come up with a benchmark where the tag allocation is enough of
a bottleneck to see huge benefits. My synthetic test module [2], which
does the scale_bitmap operations directly, shows much better results.

This survived a quick run of xfstests and a battery of benchmarks.
Applies to 4.8-rc5.

Thanks!

1: http://marc.info/?l=linux-block&m=147251402805405&w=2
2: https://github.com/osandov/osandov-linux/blob/master/modules/scale_bitmap_benchmark/scale_bitmap_benchmark.c

Omar Sandoval (5):
blk-mq: abstract tag allocation out into scale_bitmap library
scale_bitmap: allocate wait queues on a specific node
scale_bitmap: push per-cpu last_tag into scale_bitmap_queue
scale_bitmap: push alloc policy into scale_bitmap_queue
scale_bitmap: randomize initial last_cache values

MAINTAINERS | 1 +
block/Kconfig | 1 +
block/blk-mq-tag.c | 504 ++++++++++---------------------------------
block/blk-mq-tag.h | 42 ++--
block/blk-mq.c | 115 +++-------
block/blk-mq.h | 11 -
include/linux/blk-mq.h | 9 +-
include/linux/scale_bitmap.h | 390 +++++++++++++++++++++++++++++++++
lib/Kconfig | 3 +
lib/Makefile | 2 +
lib/scale_bitmap.c | 325 ++++++++++++++++++++++++++++
11 files changed, 887 insertions(+), 516 deletions(-)
create mode 100644 include/linux/scale_bitmap.h
create mode 100644 lib/scale_bitmap.c

--
2.9.3

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