On Tue, 2023-04-04 at 16:23 +0100, Matthew Wilcox wrote: > On Tue, Apr 04, 2023 at 02:58:50PM +0100, Matthew Wilcox (Oracle) > wrote: > > The map_pages fs method should be safe to run under the VMA lock > > instead > > of the mmap lock. This should have a measurable reduction in > > contention > > on the mmap lock. > > https://github.com/antonblanchard/will-it-scale/pull/37/files should > be a good microbenchmark to report numbers from. Obviously real- > world > benchmarks will be more compelling. > Test result in my side with page_fault4 of will-it-scale in thread mode is: 15274196 (without the patch) -> 17291444 (with the patch) 13.2% improvement on a Ice Lake with 48C/96T + 192G RAM + ext4 filesystem. The perf showed the mmap_lock contention reduced a lot: (Removed the grandson functions of do_user_addr_fault()) latest linux-next with the patch: 51.78%--do_user_addr_fault | |--49.09%--handle_mm_fault |--1.19%--lock_vma_under_rcu --1.09%--down_read latest linux-next without the patch: 73.65%--do_user_addr_fault | |--28.65%--handle_mm_fault |--17.22%--down_read_trylock |--10.92%--down_read |--9.20%--up_read --7.30%--find_vma My understanding is down_read_trylock, down_read and up_read all are related with mmap_lock. So the mmap_lock contention reduction is quite obvious. For functional testing, our 0day already cherry-picked the patchset and the testing is ongoing. If any problem hit during testing, 0day will report it out. Thanks. Regards Yin, Fengwei
