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 | Tue, 7 Aug 2018 18:51:45 -0700 |
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On 8/6/18 10:45 PM, Michal Hocko wrote: > On Mon 06-08-18 15:19:06, Yang Shi wrote: >> >> 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? > Just skip those special cases in the initial implementation and handle > each special case in its own patch on top.
Thanks. VM_LOCKED area will not be handled specially since it is easy to handle it, just follow what do_munmap does. The special cases will just handle VM_HUGETLB, VM_PFNMAP and uprobe mappings.
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