[PATCH 0/3] remove rw_page() from brd, pmem and btt

Ross Zwisler
2017-07-28T16:57:22Z

Dan Williams and Christoph Hellwig have recently expressed doubt about
whether the rw_page() interface made sense for synchronous memory drivers
[1][2]. It's unclear whether this interface has any performance benefit
for these drivers, but as we continue to fix bugs it is clear that it does
have a maintenance burden. This series removes the rw_page()
implementations in brd, pmem and btt to relieve this burden.

The last existing user of the rw_page interface is the zram driver, and
according to the changelog for the patch that added zram_rw_page() that
driver does see a clear performance gain:

I implemented the feature in zram and tested it. Test bed was the G2, LG
electronic mobile device, whtich has msm8974 processor and 2GB memory.

With a memory allocation test program consuming memory, the system
generates swap.

Operating time of swap_write_page() was measured.

--------------------------------------------------
| | operating time | improvement |
| | (20 runs average) | |
--------------------------------------------------
|with patch | 1061.15 us | +2.4% |
--------------------------------------------------
|without patch| 1087.35 us | |
--------------------------------------------------

Each test(with paged_io,with BIO) result set shows normal distribution
and has equal variance. I mean the two values are valid result to
compare. I can say operation with paged I/O(without BIO) is faster 2.4%
with confidence level 95%.

These patches have passed ext4 and XFS xfstest regression testing with
a memory mode pmem driver (without DAX), with pmem + btt and with brd.

These patches apply cleanly to the current v4.13-rc2 based linux/master.

[1] https://lists.01.org/pipermail/linux-nvdimm/2017-July/011389.html
[2] https://www.mail-archive.com/linux-block@vger.kernel.org/msg11170.html

Ross Zwisler (3):
btt: remove btt_rw_page()
pmem: remove pmem_rw_page()
brd: remove brd_rw_page()

drivers/block/brd.c | 10 ----------
drivers/nvdimm/btt.c | 15 ---------------
drivers/nvdimm/pmem.c | 21 ---------------------
3 files changed, 46 deletions(-)

--
2.9.4