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.

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