On Sun, May 10, 2015 at 2:46 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > >> > "Directly mapped pmem integrated into the page cache": >> > ------------------------------------------------------ > >> Nice, I think it makes sense as an area that gets reserved at file >> system creation time. You are not proposing that this gets >> automatically reserved at the device level, right? [...] > > Well, it's most practical if the device does it automatically (the > layout is determined prior filesystem creation), and the filesystem > does not necessarily have to be aware of it - but obviously as a user > opt-in. > Hmm, my only hesitation is that the raw size of a pmem device is visible outside of Linux (UEFI/BIOS other OSes, etc). What about a simple layered block-device that fronts a raw pmem device? It can store a small superblock signature and then reserve / init the struct page space. This is where we can use the __pfn_t flags that Linus suggested. Whereas the raw device ->direct_access() returns __pfn_t values with a 'PFN_DEV' flag indicating originating from device-memory, a ->direct_access() on this struct-page-provider-device yields __pfn_t's with 'PFN_DEV | PFN_MAPPED' indicating that __pfn_t_to_page() can attempt to lookup the page in a device-specific manner (similar to how kmap_atomic_pfn_t is implemented in the 'evacuate struct page from the block layer' patch set). -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
