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powerpc/64s/radix: Enable HAVE_ARCH_HUGE_VMAP

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This sets the HAVE_ARCH_HUGE_VMAP option, and defines the required
page table functions.

This enables huge (2MB and 1GB) ioremap mappings. I don't have a
benchmark for this change, but huge vmap will be used by a later core
kernel change to enable huge vmalloc memory mappings. This improves
cached `git diff` performance by about 5% on a 2-node POWER9 with 32MB
size dentry cache hash.

  Profiling git diff dTLB misses with a vanilla kernel:

  81.75%  git      [kernel.vmlinux]    [k] __d_lookup_rcu
   7.21%  git      [kernel.vmlinux]    [k] strncpy_from_user
   1.77%  git      [kernel.vmlinux]    [k] find_get_entry
   1.59%  git      [kernel.vmlinux]    [k] kmem_cache_free

            40,168      dTLB-miss
       0.100342754 seconds time elapsed

  With powerpc huge vmalloc:

             2,987      dTLB-miss
       0.095933138 seconds time elapsed

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin
2019-06-10 13:08:18 +10:00
committed by Michael Ellerman
parent d38153f9cc
commit d909f9109c
4 changed files with 110 additions and 1 deletions
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2
Documentation/admin-guide/kernel-parameters.txt
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@@ -2927,7 +2927,7 @@
register save and restore. The kernel will only save
legacy floating-point registers on task switch.
nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.