On Wed, Aug 26, 2015 at 09:34:20PM +0000, Williams, Dan J wrote: > On Wed, 2015-08-26 at 14:41 +0200, Christoph Hellwig wrote: > > I like the intent behind this, but not the implementation. > > > > I think the right approach is to keep the defaults in linux/pmem.h > > and simply not set CONFIG_ARCH_HAS_PMEM_API for x86-32. > > Yes, that makes things much cleaner. Revised patch and changelog below: > > 8<---- > Subject: x86, pmem: clarify that ARCH_HAS_PMEM_API implies PMEM mapped WB > > From: Dan Williams <dan.j.williams@xxxxxxxxx> > > Given that a write-back (WB) mapping plus non-temporal stores is > expected to be the most efficient way to access PMEM, update the > definition of ARCH_HAS_PMEM_API to imply arch support for > WB-mapped-PMEM. This is needed as a pre-requisite for adding PMEM to > the direct map and mapping it with struct page. > > The above clarification for X86_64 means that memcpy_to_pmem() is > permitted to use the non-temporal arch_memcpy_to_pmem() rather than > needlessly fall back to default_memcpy_to_pmem() when the pcommit > instruction is not available. When arch_memcpy_to_pmem() is not > guaranteed to flush writes out of cache, i.e. on older X86_32 > implementations where non-temporal stores may just dirty cache, > ARCH_HAS_PMEM_API is simply disabled. > > The default fall back for persistent memory handling remains. Namely, > map it with the WT (write-through) cache-type and hope for the best. > > arch_has_pmem_api() is updated to only indicate whether the arch > provides the proper helpers to meet the minimum "writes are visible > outside the cache hierarchy after memcpy_to_pmem() + wmb_pmem()". Code > that cares whether wmb_pmem() actually flushes writes to pmem must now > call arch_has_wmb_pmem() directly. > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Toshi Kani <toshi.kani@xxxxxx> > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > [hch: set ARCH_HAS_PMEM_API=n on X86_32] > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Yep, this seems like a good change. Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> -- 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>