On Tue, Mar 14, 2023 at 06:29:24PM +0800, Haifeng Xu wrote: > > > On 2023/3/14 17:09, David Hildenbrand wrote: > > On 14.03.23 09:05, Haifeng Xu wrote: > >> > >> > >> On 2023/3/8 17:13, David Hildenbrand wrote: > >>> 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 ;) ). > >>> > >> > >> Hi Daivd, the details of test result were posted last week. Do you have any suggestions or more concerns about this change? > > > > No, I guess it really doesn't matter performance wise. > > > > One valid question would be: why perform this change at all? The redundancy doesn't seem to harm performance either. > > > > If the change would obviously improve code readability it would be easy to justify. I'm not convinced, that is the case, but maybe for others. > > Yes, this change doesn't optimize performance, just improve the code readability. > It seems that nobody ack this change, should I change the commit message and resend this patch? I don't see the point of this patch. Just drop it.
