On Fri, Apr 25, 2014 at 05:01:23AM -0700, Hugh Dickins wrote: > One, regarding dirty shared mappings: you're thinking above of > mmap()'ing proper filesystem files, but this case also includes > shared memory - I expect there are uses of giant amounts of shared > memory, for which we really would prefer not to slow the teardown. > > And confusingly, those are not subject to the special page_mkclean() > constraints, but still need to be handled in a correct manner: your > patch is fine, but might be overkill for them - I'm not yet sure. I think we could look at mapping_cap_account_dirty(page->mapping) while holding the ptelock, the mapping can't go away while we hold that lock. And afaict that's the exact differentiator between these two cases. > Two, Ben said earlier that he's more worried about users of > unmap_mapping_range() than concurrent munmap(); and you said > earlier that you would almost prefer to have some special lock > to serialize with page_mkclean(). > > Er, i_mmap_mutex. > > That's what unmap_mapping_range(), and page_mkclean()'s rmap_walk, > take to iterate over the file vmas. So perhaps there's no race at all > in the unmap_mapping_range() case. And easy (I imagine) to fix the > race in Dave's racewrite.c use of MADV_DONTNEED: untested patch below. Ooh shiney.. yes that might work! > But exit and munmap() don't take i_mmap_mutex: perhaps they should > when encountering a VM_SHARED vma Well, they will of course take it in order to detach the vma from the rmap address_space::i_mmap tree. > (I believe VM_SHARED should be > peculiar to having vm_file seta, but test both below because I don't > want to oops in some odd corner where a special vma is set up). I think you might be on to something there... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>