On Wed, Jan 22, 2014 at 01:39:32PM -0500, Rik van Riel wrote: > On 01/22/2014 01:24 PM, Linus Torvalds wrote: > >On Wed, Jan 22, 2014 at 10:07 AM, Rik van Riel <r...@redhat.com> wrote: > >> > >>The difference between a numa pte and a protnone pte is > >>the VMA permissions. > > > >If that is indeed the only difference, then we should damn well get > >rid of that f*cking stupid _PAGE_NUMA name entirely. > > > >It's misleading crap. Really. Just do a quick grep for that bit, and > >you see just *how* confused people are about it: > > > > #define _PAGE_NUMA _PAGE_PROTNONE > > ... > > if ((pte_flags(a) & (_PAGE_PROTNONE | _PAGE_NUMA)) & > > > >think about it. Just *THINK* about how broken that code is. The whole > >thing is a disaster. _PAGE_NUMA must die. It's shit. > > The reason things are this way is that we were > not sure whether we can indeed use _PAGE_PROTNONE > for NUMA balancing on all architectures. >
Power is not using _PAGE_PROTNONE to trap NUMA hinting faults because they do not have that bit. Instead they reuse _PAGE_COHERENT with various tricks, patches are in -next. 92c08a0d522c7e62c01a63e42597f0c2b02c4245 powerpc/mm: Use HPTE constants when updating hpte bits c8c06f5a0dde0fed260c54d550962187f266ed0d powerpc/mm: Free up _PAGE_COHERENCE for numa fault use later 8937ba48dcf62b5cdf7abb93652914af16756f50 powerpc/mm: Only check for _PAGE_PRESENT in set_pte/pmd functions c34a51ce49b40b9667cd7f5cc2e40475af8b4c3d powerpc/mm: Enable _PAGE_NUMA for book3s As confusing as _PAGE_NUMA is, the intent was to express support in an architecture-independent manner. If we had started with _PAGE_PROTNONE then it would still be ambiguous -- are we interested in NUMA hinting information or is this really PROTNONE protection? The power people would then have had to add something like _PAGE_NUMA anyway when they had no _PAGE_PROTNONE bit or define _PAGE_PROTNONE as _PAGE_COHERENT which is just a different type of misleading. > If we are sure that _PAGE_PROTNONE can be used > everywhere, I agree we should get rid of the whole > _PAGE_NUMA naming, and replace that ambiguous > code with some comments and documentation instead. We are sure that _PAGE_PROTNONE cannot be used everywhere. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/