Re: [PATCH v13 14/14] powerpc/64s/radix: Enable huge vmalloc mappings

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Hi Nick,

Le 17/03/2021 à 07:24, Nicholas Piggin a écrit :
This reduces TLB misses by nearly 30x on a `git diff` workload on a
2-node POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%, due
to vfs hashes being allocated with 2MB pages.

Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
  .../admin-guide/kernel-parameters.txt         |  2 ++
  arch/powerpc/Kconfig                          |  1 +
  arch/powerpc/kernel/module.c                  | 22 +++++++++++++++----
  3 files changed, 21 insertions(+), 4 deletions(-)

--- a/arch/powerpc/kernel/module.c
+++ b/arch/powerpc/kernel/module.c
@@ -8,6 +8,7 @@
  #include <linux/moduleloader.h>
  #include <linux/err.h>
  #include <linux/vmalloc.h>
+#include <linux/mm.h>
  #include <linux/bug.h>
  #include <asm/module.h>
  #include <linux/uaccess.h>
@@ -87,13 +88,26 @@ int module_finalize(const Elf_Ehdr *hdr,
  	return 0;
  }
-#ifdef MODULES_VADDR
  void *module_alloc(unsigned long size)
  {
+	unsigned long start = VMALLOC_START;
+	unsigned long end = VMALLOC_END;
+
+#ifdef MODULES_VADDR
  	BUILD_BUG_ON(TASK_SIZE > MODULES_VADDR);
+	start = MODULES_VADDR;
+	end = MODULES_END;
+#endif
+
+	/*
+	 * Don't do huge page allocations for modules yet until more testing
+	 * is done. STRICT_MODULE_RWX may require extra work to support this
+	 * too.
+	 */
- return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END, GFP_KERNEL,
-				    PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,


I think you should add the following in <asm/pgtable.h>

#ifndef MODULES_VADDR
#define MODULES_VADDR VMALLOC_START
#define MODULES_END VMALLOC_END
#endif

And leave module_alloc() as is (just removing the enclosing #ifdef MODULES_VADDR and adding the VM_NO_HUGE_VMAP flag)

This would minimise the conflits with the changes I did in powerpc/next reported by Stephen R.

+	return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL,
+				    PAGE_KERNEL_EXEC,
+				    VM_NO_HUGE_VMAP | VM_FLUSH_RESET_PERMS,
+				    NUMA_NO_NODE,
  				    __builtin_return_address(0));
  }
-#endif




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