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
