On Mon, May 22, 2017 at 9:51 AM, Jérôme Glisse <jglisse@xxxxxxxxxx> wrote: > HMM (heterogeneous memory management) need struct page to support migration > from system main memory to device memory. Reasons for HMM and migration to > device memory is explained with HMM core patch. > > This patch deals with device memory that is un-addressable memory (ie CPU > can not access it). Hence we do not want those struct page to be manage > like regular memory. That is why we extend ZONE_DEVICE to support different > types of memory. > > A persistent memory type is define for existing user of ZONE_DEVICE and a > new device un-addressable type is added for the un-addressable memory type. > There is a clear separation between what is expected from each memory type > and existing user of ZONE_DEVICE are un-affected by new requirement and new > use of the un-addressable type. All specific code path are protect with > test against the memory type. > > Because memory is un-addressable we use a new special swap type for when > a page is migrated to device memory (this reduces the number of maximum > swap file). > > The main two additions beside memory type to ZONE_DEVICE is two callbacks. > First one, page_free() is call whenever page refcount reach 1 (which means > the page is free as ZONE_DEVICE page never reach a refcount of 0). This > allow device driver to manage its memory and associated struct page. > > The second callback page_fault() happens when there is a CPU access to > an address that is back by a device page (which are un-addressable by the > CPU). This callback is responsible to migrate the page back to system > main memory. Device driver can not block migration back to system memory, > HMM make sure that such page can not be pin into device memory. > > If device is in some error condition and can not migrate memory back then > a CPU page fault to device memory should end with SIGBUS. > > Changed since v1: > - rename to device private memory (from device unaddressable) > > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> [..] > diff --git a/mm/Kconfig b/mm/Kconfig > index 229afe3..d49d816 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -737,6 +737,19 @@ config ZONE_DEVICE > > If FS_DAX is enabled, then say Y. > > +config DEVICE_UNADDRESSABLE > + bool "Unaddressable device memory (GPU memory, ...)" > + depends on X86_64 > + depends on ZONE_DEVICE > + depends on MEMORY_HOTPLUG > + depends on MEMORY_HOTREMOVE > + depends on SPARSEMEM_VMEMMAP > + > + help > + Allows creation of struct pages to represent unaddressable device > + memory; i.e., memory that is only accessible from the device (or > + group of devices). Lets change config symbol naming from "device un-addressable memory" to "device private memory" the same way we did for the code symbols. With that change you can add: Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx> -- 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
