On Tue, May 15, 2018 at 09:46:01AM +0200, Martijn Coenen wrote: < snip >
> >> About the unmap at runtime part, your commit message was a bit confusing. > >> You > >> said "every binder buffers should be mapped in advance by binder_mmap." > >> but I > >> think the new binder shrinker mechanism doesn't make that true anymore. > > > > It's good point. I didn't know know that. > > When I see binder_vm_fault, it emits SIGBUS. That means shrinker cannot zap > > pages > > process is using, I think. IOW, every pages for binder are mapped at mmap > > time > > and is never mapped in runtime by page fault. Right? > > Right - the address range is allocated once, and an initial amount of > pages is mapped into it. For every transaction into that process, we > will see if there's enough pages, and if not allocate so that we have > enough of them - so this is not done by page fault. The shrinker won't > touch pages for which a transaction is in progress. Of course a > process itself could still try to read from an unallocated address, > but in that case returning SIGBUS and having that process crash seems > fine. Thanks for the confirmation. > > I'm also not sure the read lock is needed, but I would need to read a > whole lot more code to convince myself it's not. For page zapping, we shouldn't need mmap_sem write lock. We should replace it with down_read/write, too. Thanks.
