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

[Christophe Leroy]

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