[PATCH v4 0/4] io_uring/rsrc: coalescing multi-hugepage registered buffers

[Chenliang Li <cliang01.li@samsung.com>]

Registered buffers are stored and processed in the form of bvec array,
each bvec element typically points to a PAGE_SIZE page but can also work
with hugepages. Specifically, a buffer consisting of a hugepage is
coalesced to use only one hugepage bvec entry during registration.
This coalescing feature helps to save both the space and DMA-mapping time.

However, currently the coalescing feature doesn't work for multi-hugepage
buffers. For a buffer with several 2M hugepages, we still split it into
thousands of 4K page bvec entries while in fact, we can just use a
handful of hugepage bvecs.

This patch series enables coalescing registered buffers with more than
one hugepages. It optimizes the DMA-mapping time and saves memory for
these kind of buffers.

Testing:

The hugepage fixed buffer I/O can be tested using fio without
modification. The fio command used in the following test is given
in [1]. There's also a liburing testcase in [2]. Also, the system
should have enough hugepages available before testing.

Perf diff of 8M(4 * 2M hugepages) fio randread test:

Before          After           Symbol
.....................................................
4.68%				[k] __blk_rq_map_sg
3.31%				[k] dma_direct_map_sg
2.64%				[k] dma_pool_alloc
1.09%				[k] sg_next
                +0.49%		[k] dma_map_page_attrs

Perf diff of 8M fio randwrite test:

Before		After		Symbol
......................................................
2.82%				[k] __blk_rq_map_sg
2.05%				[k] dma_direct_map_sg
1.75%				[k] dma_pool_alloc
0.68%				[k] sg_next
		+0.08%		[k] dma_map_page_attrs

First three patches prepare for adding the multi-hugepage coalescing
into buffer registration, the 4th patch enables the feature. 

-----------------
Changes since v3:

- Delete unnecessary commit message
- Update test command and test results

v3 : https://lore.kernel.org/io-uring/20240514001614.566276-1-cliang01.li@samsung.com/T/#t

Changes since v2:

- Modify the loop iterator increment to make code cleaner
- Minor fix to the return procedure in coalesced buffer account
- Correct commit messages
- Add test cases in liburing

v2 : https://lore.kernel.org/io-uring/20240513020149.492727-1-cliang01.li@samsung.com/T/#t

Changes since v1:

- Split into 4 patches
- Fix code style issues
- Rearrange the change of code for cleaner look
- Add speciallized pinned page accounting procedure for coalesced
  buffers
- Reordered the newly add fields in imu struct for better compaction

v1 : https://lore.kernel.org/io-uring/20240506075303.25630-1-cliang01.li@samsung.com/T/#u

[1]
fio -iodepth=64 -rw=randread(-rw=randwrite) -direct=1 -ioengine=io_uring \
-bs=8M -numjobs=1 -group_reporting -mem=shmhuge -fixedbufs -hugepage-size=2M \
-filename=/dev/nvme0n1 -runtime=10s -name=test1

[2]
https://lore.kernel.org/io-uring/20240514051343.582556-1-cliang01.li@samsung.com/T/#u

Chenliang Li (4):
  io_uring/rsrc: add hugepage buffer coalesce helpers
  io_uring/rsrc: store folio shift and mask into imu
  io_uring/rsrc: add init and account functions for coalesced imus
  io_uring/rsrc: enable multi-hugepage buffer coalescing

 io_uring/rsrc.c | 217 +++++++++++++++++++++++++++++++++++++++---------
 io_uring/rsrc.h |  12 +++
 2 files changed, 191 insertions(+), 38 deletions(-)


base-commit: 59b28a6e37e650c0d601ed87875b6217140cda5d
-- 
2.34.1