On Thu, Nov 9, 2017 at 9:30 AM, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > On Thu, 9 Nov 2017, Dan Williams wrote: > >> On Thu, Nov 9, 2017 at 8:40 AM, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: >> > >> > >> > On Wed, 8 Nov 2017, Dan Williams wrote: >> > >> >> On Wed, Nov 8, 2017 at 12:15 PM, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: >> >> > >> >> > >> >> > On Wed, 8 Nov 2017, Dan Williams wrote: >> >> > >> >> >> On Wed, Nov 8, 2017 at 7:35 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> >> > On Wed, Nov 08, 2017 at 10:21:38AM -0500, Mikulas Patocka wrote: >> >> >> >> > And what do you do for an architecture with virtuall indexed caches? >> >> >> >> >> >> >> >> Persistent memory is not supported on such architectures - it is only >> >> >> >> supported on x86-64 and arm64. >> >> >> > >> >> >> > For now. But once support is added your driver will just corrupt data >> >> >> > unless you have the right API in place. >> >> >> >> >> >> I'm also in the process of ripping out page-less dax support. With >> >> >> pages we can potentially leverage the VIVT-cache support in some >> >> >> architectures, likely with more supporting infrastructure for >> >> >> dax_flush(). >> >> > >> >> > Should I remove all the code for page-less persistent memory from my >> >> > driver? >> >> > >> >> >> >> Yes, that would be my recommendation. You can see that filesystem-dax >> >> is on its way to dropping page-less support in this series: >> >> >> >> https://lists.01.org/pipermail/linux-nvdimm/2017-October/013125.html >> > >> > Why do you indend to drop dax for ramdisk? It's perfect for testing. >> > >> > On x86, persistent memory can be tested with the memmap kernel parameters, >> > but on other architectures, ramdisk is the only option for tests. >> > >> >> Because it's not "perfect for testing", it does not support the >> get_user_pages() model that we need to safely handle DAX dma. ARM64 >> and PowerPC PMEM support is in the works, so I expect the architecture >> support landscape for major architectures to improve such that the >> pmem driver can always be used for DAX testing. > > Yes - but if I want to test the persistent memory driver on big-endian > machine, I could use an old Sparc or PA-RISC machine with ramdisk. > > New PowerPC machines may support native persistent memory, but they are > extremely expensive. > Ok, but for testing purposes we can just enable a "compile-test" / fake "ARCH_HAS_PMEM_API" configuration to enable pmem usage on other archs which would enable a better test case than DAX with brd. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
