On Wed, Dec 14, 2016 at 07:15:15AM +1100, Dave Chinner wrote: > On Tue, Dec 13, 2016 at 01:15:11PM -0500, Jerome Glisse wrote: > > I would like to discuss un-addressable device memory in the context of > > filesystem and block device. Specificaly how to handle write-back, read, > > ... when a filesystem page is migrated to device memory that CPU can not > > access. > > You mean pmem that is DAX-capable that suddenly, without warning, > becomes non-DAX capable? > > If you are not talking about pmem and DAX, then exactly what does > "when a filesystem page is migrated to device memory that CPU can > not access" mean? What "filesystem page" are we talking about that > can get migrated from main RAM to something the CPU can't access? I am talking about GPU, FPGA, ... any PCIE device that have fast on board memory that can not be expose transparently to the CPU. I am reusing ZONE_DEVICE for this, you can see HMM patchset on linux-mm https://lwn.net/Articles/706856/ So in my case i am only considering non DAX/PMEM filesystem ie any "regular" filesystem back by a "regular" block device. I want to be able to migrate mmaped area of such filesystem to device memory while the device is actively using that memory. >From kernel point of view such memory is almost like any other, it has a struct page and most of the mm code is non the wiser, nor need to be about it. CPU access trigger a migration back to regular CPU accessible page. But for thing like writeback i want to be able to do writeback with- out having to migrate page back first. So that data can stay on the device while writeback is happening. 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>