On 10/16/18 9:43 PM, Joel Fernandes wrote: > On Tue, Oct 16, 2018 at 01:29:52PM +0200, Vlastimil Babka wrote: >> On 10/16/18 12:33 AM, Joel Fernandes wrote: >>> On Mon, Oct 15, 2018 at 02:42:09AM -0700, Christoph Hellwig wrote: >>>> On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote: >>>>> Android needs to mremap large regions of memory during memory management >>>>> related operations. >>>> >>>> Just curious: why? >>> >>> In Android we have a requirement of moving a large (up to a GB now, but may >>> grow bigger in future) memory range from one location to another. >> >> I think Christoph's "why?" was about the requirement, not why it hurts >> applications. I admit I'm now also curious :) > > This issue was discovered when we wanted to be able to move the physical > pages of a memory range to another location quickly so that, after the > application threads are resumed, UFFDIO_REGISTER_MODE_MISSING userfaultfd > faults can be received on the original memory range. The actual operations > performed on the memory range are beyond the scope of this discussion. The > user threads continue to refer to the old address which will now fault. The > reason we want retain the old memory range and receives faults there is to > avoid the need to fix the addresses all over the address space of the threads > after we finish with performing operations on them in the fault handlers, so > we mremap it and receive faults at the old addresses. > > Does that answer your question? Yes, interesting, thanks! Vlastimil > thanks, > > - Joel >
