On Fri, Apr 28, 2017 at 11:00 AM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> On Fri, Apr 28, 2017 at 10:34 AM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> >> Kirill points out that the calls to {get,put}_dev_pagemap() can be >> >> removed from the mm fast path if we take a single get_dev_pagemap() >> >> reference to signify that the page is alive and use the final put of the >> >> page to drop that reference. >> >> >> >> This does require some care to make sure that any waits for the >> >> percpu_ref to drop to zero occur *after* devm_memremap_page_release(), >> >> since it now maintains its own elevated reference. >> > >> > This is NAK from HMM point of view as i need those call. So if you remove >> > them now i will need to add them back as part of HMM. >> >> I thought you only need them at page free time? You can still hook >> __put_page(). > > No, i need a hook when page refcount reach 1, not 0. That being said > i don't care about put_dev_pagemap(page->pgmap); so that part of the > patch is fine from HMM point of view but i definitly need to hook my- > self in the general put_page() function. > > So i will have to undo part of this patch for HMM (put_page() will > need to handle ZONE_DEVICE page differently). Ok, I'd rather this go in now since it fixes the existing use case, and unblocks the get_user_pages_fast() conversion to generic code. That also gives Kirill and -mm folks a chance to review what HMM wants to do on top of the page_ref infrastructure. The {get,put}_zone_device_page interface went in in 4.5 right before page_ref went in during 4.6, so it was just an oversight that {get,put}_zone_device_page were not removed earlier. -- 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>