Messages in this thread | | | Subject | Re: [RFC v3 PATCH 4/5] mm: mmap: zap pages with read mmap_sem for large mapping | From | Yang Shi <> | Date | Fri, 29 Jun 2018 21:26:23 -0700 |
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On 6/29/18 8:15 PM, Andrew Morton wrote: > On Fri, 29 Jun 2018 19:28:15 -0700 Yang Shi <yang.shi@linux.alibaba.com> wrote: > >> >>> we're adding a bunch of code to 32-bit kernels which will never be >>> executed. >>> >>> I'm thinking it would be better to be much more explicit with "#ifdef >>> CONFIG_64BIT" in this code, rather than relying upon the above magic. >>> >>> But I tend to think that the fact that we haven't solved anything on >>> locked vmas or on uprobed mappings is a shostopper for the whole >>> approach :( >> I agree it is not that perfect. But, it still could improve the most use >> cases. > Well, those unaddressed usecases will need to be fixed at some point.
Yes, definitely.
> What's our plan for that?
As I mentioned in the earlier email, locked and hugetlb cases might be able to be solved by separating vm_flags update and actual unmap. I will look into it further later.
From my point of view, uprobe mapping sounds not that vital.
> > Would one of your earlier designs have addressed all usecases? I > expect the dumb unmap-a-little-bit-at-a-time approach would have?
Yes. The v1 design does unmap with holding write map_sem. So, the vm_flags update is not a problem.
Thanks, Yang
> >> For the locked vmas and hugetlb vmas, unmapping operations need modify >> vm_flags. But, I'm wondering we might be able to separate unmap and >> vm_flags update. Because we know they will be unmapped right away, the >> vm_flags might be able to be updated in write mmap_sem critical section >> before the actual unmap is called or after it. This is just off the top >> of my head. >> >> For uprobed mappings, I'm not sure how vital it is to this case. >> >> Thanks, >> Yang >>
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