On Tue, Jul 18, 2017 at 11:26:51AM +0800, Bob Liu wrote: > On 2017/7/14 5:15, Jérôme Glisse wrote: > > Sorry i made horrible mistake on names in v4, i completly miss- > > understood the suggestion. So here i repost with proper naming. > > This is the only change since v3. Again sorry about the noise > > with v4. > > > > Changes since v4: > > - s/DEVICE_HOST/DEVICE_PUBLIC > > > > Git tree: > > https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-cdm-v5 > > > > > > Cache coherent device memory apply to architecture with system bus > > like CAPI or CCIX. Device connected to such system bus can expose > > their memory to the system and allow cache coherent access to it > > from the CPU. > > > > Even if for all intent and purposes device memory behave like regular > > memory, we still want to manage it in isolation from regular memory. > > Several reasons for that, first and foremost this memory is less > > reliable than regular memory if the device hangs because of invalid > > commands we can loose access to device memory. Second CPU access to > > this memory is expected to be slower than to regular memory. Third > > having random memory into device means that some of the bus bandwith > > wouldn't be available to the device but would be use by CPU access. > > > > This is why we want to manage such memory in isolation from regular > > memory. Kernel should not try to use this memory even as last resort > > when running out of memory, at least for now. > > > > I think set a very large node distance for "Cache Coherent Device Memory" > may be a easier way to address these concerns. Such approach was discuss at length in the past see links below. Outcome of discussion: - CPU less node are bad - device memory can be unreliable (device hang) no way for application to understand that - application and driver NUMA madvise/mbind/mempolicy ... can conflict with each other and no way the kernel can figure out which should apply - NUMA as it is now would not work as we need further isolation that what a large node distance would provide Probably few others argument i forget. https://lists.gt.net/linux/kernel/2551369 https://groups.google.com/forum/#!topic/linux.kernel/Za_e8C3XnRs%5B1-25%5D https://lwn.net/Articles/720380/ Cheers, Jérôme -- 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>
