On Mon, Nov 21, 2016 at 11:44:36AM +1100, Balbir Singh wrote: > > > On 19/11/16 05:18, Jérôme Glisse wrote: > > Only usefull for arch where we support ZONE_DEVICE and where we want to > > also support un-addressable device memory. We need struct page for such > > un-addressable memory. But we should avoid populating the kernel linear > > mapping for the physical address range because there is no real memory > > or anything behind those physical address. > > > > Hence we need more flags than just knowing if it is device memory or not. > > > > > Isn't it better to add a wrapper to arch_add/remove_memory and do those > checks inside and then call arch_add/remove_memory to reduce the churn. > If you need selectively enable MEMORY_UNADDRESSABLE that can be done with > _ARCH_HAS_FEATURE The flag parameter can be use by other new features and thus i thought the churn was fine. But i do not mind either way, whatever people like best. [...] > > -extern int arch_add_memory(int nid, u64 start, u64 size, bool for_device); > > + > > +/* > > + * For device memory we want more informations than just knowing it is device > information > > + * memory. We want to know if we can migrate it (ie it is not storage memory > > + * use by DAX). Is it addressable by the CPU ? Some device memory like GPU > > + * memory can not be access by CPU but we still want struct page so that we > accessed > > + * can use it like regular memory. > > Can you please add some details on why -- migration needs them for example? I am not sure what you mean ? DAX ie persistent memory device is intended to be use for filesystem or persistent storage. Hence memory migration does not apply to it (it would go against its purpose). So i want to extend ZONE_DEVICE to be more then just DAX/persistent memory. For that i need to differentatiate between device memory that can be migrated and should be more or less treated like regular memory (with struct page). This is what the MEMORY_MOVABLE flag is for. Finaly in my case the device memory is not accessible by the CPU so i need yet another flag. In the end i am extending ZONE_DEVICE to be use for 3 differents type of memory. Is this the kind of explanation you are looking for ? > > + */ > > +#define MEMORY_FLAGS_NONE 0 > > +#define MEMORY_DEVICE (1 << 0) > > +#define MEMORY_MOVABLE (1 << 1) > > +#define MEMORY_UNADDRESSABLE (1 << 2) 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>