Messages in this thread | | | Date | Thu, 11 Nov 2021 21:01:43 +0800 | Subject | Re: [PATCH v3 00/15] Free user PTE page table pages | From | Qi Zheng <> |
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On 11/11/21 8:51 PM, David Hildenbrand wrote:
>>>> >>>> In the performance test shown on the cover, we repeatedly performed >>>> touch and madvise(MADV_DONTNEED) actions, which simulated the case >>>> you said above. >>>> >>>> We did find a small amount of performance regression, but I think it is >>>> acceptable, and no new perf hotspots have been added. >>> >>> That test always accesses 2MiB and does it from a single thread. Things >>> might (IMHO will) look different when only accessing individual pages >>> and doing the access from one/multiple separate threads (that's what >> >> No, it includes multi-threading: >> > > Oh sorry, I totally skipped [2]. > >> while (1) { >> char *c; >> char *start = mmap_area[cpu]; >> char *end = mmap_area[cpu] + FAULT_LENGTH; >> pthread_barrier_wait(&barrier); >> //printf("fault into %p-%p\n",start, end); >> >> for (c = start; c < end; c += PAGE_SIZE) >> *c = 0; >> >> pthread_barrier_wait(&barrier); >> for (i = 0; cpu==0 && i < num; i++) >> madvise(mmap_area[i], FAULT_LENGTH, MADV_DONTNEED); >> pthread_barrier_wait(&barrier); >> } >> >> Thread on cpu0 will use madvise(MADV_DONTNEED) to release the physical >> memory of threads on other cpu. >> > > I'll have a more detailed look at the benchmark. On a quick glimpse,
Thank you for your time :)
> looks like the threads are also accessing a full 2MiB range, one page at > a time, and one thread is zapping the whole 2MiB range. A single CPU > only accesses memory within one 2MiB range IIRC. > > Having multiple threads just access individual pages within a single 2 > MiB region, and having one thread zap that memory (e.g., simulate > swapout) could be another benchmark.
LGTM, I will simulate more scenarios for testing.
> > We have to make sure to run with THP disabled (e.g., using > madvise(MADV_NOHUGEPAGE) on the complete mapping in the benchmark > eventually), because otherwise you might just be populating+zapping THPs > if they would otherwise be allowed in the environment.
Yes, I turned off THP during testing:
root@~$ cat /sys/kernel/mm/transparent_hugepage/enabled always madvise [never]
>
-- Thanks, Qi
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