Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

Christoph Hellwig
2020-11-04T19:11:18Z

On Wed, Nov 04, 2020 at 03:02:14PM -0400, Jason Gunthorpe wrote:
> I saw that once and I really couldn't make sense of it..
> What use is having futex's that only work on THP pages? Confused
>
> CH said there was no case of HAVE_FAST_GUP !ARCH_HAS_PTE_SPECIAL, is
> one hidden someplace then?

ARCH_HAS_PTE_SPECIAL is selected by:

arc
arm (if LPAE)
arm64
mips (if !(32BIT && CPU_HAS_RIXI))
powerpc
riscv
s390
sh
sparc (if SPARC64)
x86

HAVE_FAST_GUP is supported by:

arm (if LPAE)
arm64
mips
powerpc
s390
sh
x86

so mips would be a candidate. But I think only in theory, as
the options selecting CPU_HAS_RIXI do not select
CPU_SUPPORTS_HUGEPAGES. Adding the mips maintainer to double check
my logic.