Messages in this thread | | | Date | Wed, 8 Mar 2023 10:13:15 +0100 | Subject | Re: [PATCH] mm: remove redundant check in handle_mm_fault | From | David Hildenbrand <> |
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On 08.03.23 10:03, Haifeng Xu wrote: > > > On 2023/3/7 10:48, Matthew Wilcox wrote: >> On Tue, Mar 07, 2023 at 10:36:55AM +0800, Haifeng Xu wrote: >>> On 2023/3/6 21:49, David Hildenbrand wrote: >>>> On 06.03.23 03:49, Haifeng Xu wrote: >>>>> mem_cgroup_oom_synchronize() has checked whether current memcg_in_oom is >>>>> set or not, so remove the check in handle_mm_fault(). >>>> >>>> "mem_cgroup_oom_synchronize() will returned immediately if memcg_in_oom is not set, so remove the check from handle_mm_fault()". >>>> >>>> However, that requires now always an indirect function call -- do we care about dropping that optimization? >>>> >>>> >>> >>> If memcg_in_oom is set, we will check it twice, one is from handle_mm_fault(), the other is from mem_cgroup_oom_synchronize(). That seems a bit redundant. >>> >>> if memcg_in_oom is not set, mem_cgroup_oom_synchronize() returns directly. Though it's an indirect function call, but the time spent can be negligible >>> compare to the whole mm user falut preocess. And that won't cause stack overflow error. >> >> I suggest you measure it. > > test steps: > 1) Run command: ./mmap_anon_test(global alloc, so the memcg_in_oom is not set) > 2) Calculate the quotient of cost time and page-fault counts, run 10 rounds and average the results. > > The test result shows that whether using indirect function call or not, the time spent in user fault > is almost the same, about 2.3ms.
I guess most of the benchmark time is consumed by allocating fresh pages in your test (also, why exactly do you use MAP_SHARED?).
Is 2.3ms the total time for writing to that 1GiB of memory or how did you derive that number? Posting both results would be cleaner (with more digits ;) ).
-- Thanks,
David / dhildenb
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