Messages in this thread | | | Subject | Re: [RFC v6 PATCH 2/2] mm: mmap: zap pages with read mmap_sem in munmap | From | Yang Shi <> | Date | Mon, 6 Aug 2018 15:19:06 -0700 |
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On 8/6/18 1:52 PM, Michal Hocko wrote: > On Mon 06-08-18 13:48:35, Yang Shi wrote: >> >> On 8/6/18 1:41 PM, Michal Hocko wrote: >>> On Mon 06-08-18 09:46:30, Yang Shi wrote: >>>> On 8/6/18 2:40 AM, Michal Hocko wrote: >>>>> On Fri 03-08-18 14:01:58, Yang Shi wrote: >>>>>> On 8/3/18 2:07 AM, Michal Hocko wrote: >>>>>>> On Fri 27-07-18 02:10:14, Yang Shi wrote: >>> [...] >>>>>>>> If the vma has VM_LOCKED | VM_HUGETLB | VM_PFNMAP or uprobe, they are >>>>>>>> considered as special mappings. They will be dealt with before zapping >>>>>>>> pages with write mmap_sem held. Basically, just update vm_flags. >>>>>>> Well, I think it would be safer to simply fallback to the current >>>>>>> implementation with these mappings and deal with them on top. This would >>>>>>> make potential issues easier to bisect and partial reverts as well. >>>>>> Do you mean just call do_munmap()? It sounds ok. Although we may waste some >>>>>> cycles to repeat what has done, it sounds not too bad since those special >>>>>> mappings should be not very common. >>>>> VM_HUGETLB is quite spread. Especially for DB workloads. >>>> Wait a minute. In this way, it sounds we go back to my old implementation >>>> with special handling for those mappings with write mmap_sem held, right? >>> Yes, I would really start simple and add further enhacements on top. >> If updating vm_flags with read lock is safe in this case, we don't have to >> do this. The only reason for this special handling is about vm_flags update. > > Yes, maybe you are right that this is safe. I would still argue to have > it in a separate patch for easier review, bisectability etc...
Sorry, I'm a little bit confused. Do you mean I should have the patch *without* handling the special case (just like to assume it is safe to update vm_flags with read lock), then have the other patch on top of it, which simply calls do_munmap() to deal with the special cases?
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