On Sat, Apr 29, 2017 at 01:17:26PM +0300, Kirill A. Shutemov wrote: > On Fri, Apr 28, 2017 at 03:33:07PM -0400, Jerome Glisse wrote: > > On Fri, Apr 28, 2017 at 12:22:24PM -0700, Dan Williams wrote: > > > Are you sure about needing to hook the 2 -> 1 transition? Could we > > > change ZONE_DEVICE pages to not have an elevated reference count when > > > they are created so you can keep the HMM references out of the mm hot > > > path? > > > > 100% sure on that :) I need to callback into driver for 2->1 transition > > no way around that. If we change ZONE_DEVICE to not have an elevated > > reference count that you need to make a lot more change to mm so that > > ZONE_DEVICE is never use as fallback for memory allocation. Also need > > to make change to be sure that ZONE_DEVICE page never endup in one of > > the path that try to put them back on lru. There is a lot of place that > > would need to be updated and it would be highly intrusive and add a > > lot of special cases to other hot code path. > > Could you explain more on where the requirement comes from or point me to > where I can read about this. > HMM ZONE_DEVICE pages are use like other pages (anonymous or file back page) in _any_ vma. So i need to know when a page is freed ie either as result of unmap, exit or migration or anything that would free the memory. For zone device a page is free once its refcount reach 1 so i need to catch refcount transition from 2->1 This is the only way i can inform the device that the page is now free. See https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v21&id=52da8fe1a088b87b5321319add79e43b8372ed7d There is _no_ way around that. 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>
