Messages in this thread | | | Date | Sun, 14 Jul 2013 11:12:58 +0800 | From | Sam Ben <> | Subject | Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting |
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On 07/02/2013 10:37 AM, Zheng Liu wrote: > On Mon, Jul 01, 2013 at 09:16:46AM -0700, Dave Hansen wrote: >> On 06/28/2013 07:20 PM, Zheng Liu wrote: >>>>> IOW, a process needing to do a bunch of MAP_POPULATEs isn't >>>>> parallelizable, but one using this mechanism would be. >>> I look at the code, and it seems that we will handle MAP_POPULATE flag >>> after we release mmap_sem locking in vm_mmap_pgoff(): >>> >>> down_write(&mm->mmap_sem); >>> ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff, >>> &populate); >>> up_write(&mm->mmap_sem); >>> if (populate) >>> mm_populate(ret, populate); >>> >>> Am I missing something? >> I went and did my same test using mmap(MAP_POPULATE)/munmap() pair >> versus using MADV_POPULATE in 160 threads in parallel. >> >> MADV_POPULATE was about 10x faster in the threaded configuration. >> >> With MADV_POPULATE, the biggest cost is shipping the mmap_sem cacheline >> around so that we can write the reader count update in to it. With >> mmap(), there is a lot of _contention_ on that lock which is much, much >> more expensive than simply bouncing a cacheline around. > Thanks for your explanation. > > FWIW, it would be great if we can let MAP_POPULATE flag support shared > mappings because in our product system there has a lot of applications > that uses mmap(2) and then pre-faults this mapping. Currently these > applications need to pre-fault the mapping manually.
How do you pre-fault the mapping manually in your product system? By walking through the file touching each page?
> > Regards, > - Zheng > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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