On 28/02/2023 21:37, Matthew Wilcox (Oracle) wrote: > This patchset changes the API used by the MM to set up page table entries. > The four APIs are: > set_ptes(mm, addr, ptep, pte, nr) > update_mmu_cache_range(vma, addr, ptep, nr) > flush_dcache_folio(folio) > flush_icache_pages(vma, page, nr) > > flush_dcache_folio() isn't technically new, but no architecture > implemented it, so I've done that for you. The old APIs remain around > but are mostly implemented by calling the new interfaces. > > The new APIs are based around setting up N page table entries at once. > The N entries belong to the same PMD, the same folio and the same VMA, > so ptep++ is a legitimate operation, and locking is taken care of for > you. Some architectures can do a better job of it than just a loop, > but I have hesitated to make too deep a change to architectures I don't > understand well. > > One thing I have changed in every architecture is that PG_arch_1 is now a > per-folio bit instead of a per-page bit. This was something that would > have to happen eventually, and it makes sense to do it now rather than > iterate over every page involved in a cache flush and figure out if it > needs to happen. > > The point of all this is better performance, and Fengwei Yin has > measured improvement on x86. I suspect you'll see improvement on > your architecture too. Try the new will-it-scale test mentioned here: > https://lore.kernel.org/linux-mm/20230206140639.538867-5-fengwei.yin@xxxxxxxxx/ > You'll need to run it on an XFS filesystem and have > CONFIG_TRANSPARENT_HUGEPAGE set. > > For testing, I've only run the code on x86. If an x86->foo compiler > exists in Debian, I've built defconfig. I'm relying on the buildbots > to tell me what I missed, and people who actually have the hardware to > tell me if it actually works. > > I'd like to get this into the MM tree soon after the current merge window > closes, so quick feedback would be appreciated. I've boot-tested the series (with the Yin's typo fix for patch 32) on arm64 FVP and Ampere Altra. On the Altra, I also ran page_fault4 from will-it-scale, and see ~35% improvement from this series. So: Tested-by: Ryan Roberts <ryan.roberts@xxxxxxx> Thanks, Ryan
