On Tue, May 30, 2017 at 10:43:55AM -0600, Ross Zwisler wrote: > On Wed, May 24, 2017 at 01:20:16PM -0400, Jérôme Glisse 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 v2: > > - s/DEVICE_UNADDRESSABLE/DEVICE_PRIVATE > > Changed since v1: > > - rename to device private memory (from device unaddressable) > > > > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > > Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > > --- > <> > > @@ -35,18 +37,88 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start) > > } > > #endif > > > > +/* > > + * Specialize ZONE_DEVICE memory into multiple types each having differents > > + * usage. > > + * > > + * MEMORY_DEVICE_PUBLIC: > > + * Persistent device memory (pmem): struct page might be allocated in different > > + * memory and architecture might want to perform special actions. It is similar > > + * to regular memory, in that the CPU can access it transparently. However, > > + * it is likely to have different bandwidth and latency than regular memory. > > + * See Documentation/nvdimm/nvdimm.txt for more information. > > + * > > + * MEMORY_DEVICE_PRIVATE: > > + * Device memory that is not directly addressable by the CPU: CPU can neither > > + * read nor write _UNADDRESSABLE memory. In this case, we do still have struct > _PRIVATE > > Just noticed that one holdover from the DEVICE_UNADDRESSABLE naming. > Thanks for catching that, Andrew can you change it yourself to _PRIVATE s/_UNADDRESSABLE/_PRIVATE Or should i repost fixed patch ? 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>
