Messages in this thread | | | Subject | Re: [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping | From | Yang Shi <> | Date | Wed, 11 Jul 2018 10:08:52 -0700 |
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On 7/11/18 4:53 AM, Michal Hocko wrote: > On Wed 11-07-18 14:13:12, Kirill A. Shutemov wrote: >> On Wed, Jul 11, 2018 at 12:33:12PM +0200, Michal Hocko wrote: >>> this is not a small change for something that could be achieved >>> from the userspace trivially (just call madvise before munmap - library >>> can hide this). Most workloads will even not care about races because >>> they simply do not play tricks with mmaps and userspace MM. So why do we >>> want to put the additional complexity into the kernel? >> As I said before, kernel latency issues have to be addressed in kernel. >> We cannot rely on userspace being kind here. > Those who really care and create really large mappings will know how to > do this properly. Most others just do not care enough. So I am not > really sure this alone is a sufficient argument. > > I personally like the in kernel auto tuning but as I've said the > changelog should be really clear why all the complications are > justified. This would be a lot easier to argue about if it was a simple > if (len > THARSHOLD) > do_madvise(DONTNEED) > munmap().
The main difference AFAICS, is it can't deal with the parallel faults and those special mappings. Someone may not care about it, but someone may.
Yang
> approach. But if we really have to care about parallel faults and munmap > consitency this will always be tricky
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