[4/4] powerpc/mm: Split hash page table sizing heuristic into a helper

htab_get_table_size() either retrieve the size of the hash page table (HPT)
from the device tree - if the HPT size is determined by firmware - or
uses a heuristic to determine a good size based on RAM size if the kernel
is responsible for allocating the HPT.

To support a PAPR extension allowing resizing of the HPT, we're going to
want the memory size -> HPT size logic elsewhere, so split it out into a
helper function.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 arch/powerpc/include/asm/mmu-hash64.h |  3 +++
 arch/powerpc/mm/hash_utils_64.c       | 32 +++++++++++++++++++-------------
 2 files changed, 22 insertions(+), 13 deletions(-)

David Gibson <david@gibson.dropbear.id.au> writes:

> htab_get_table_size() either retrieve the size of the hash page table (HPT)
> from the device tree - if the HPT size is determined by firmware - or
> uses a heuristic to determine a good size based on RAM size if the kernel
> is responsible for allocating the HPT.
>
> To support a PAPR extension allowing resizing of the HPT, we're going to
> want the memory size -> HPT size logic elsewhere, so split it out into a
> helper function.
>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  arch/powerpc/include/asm/mmu-hash64.h |  3 +++
>  arch/powerpc/mm/hash_utils_64.c       | 32 +++++++++++++++++++-------------
>  2 files changed, 22 insertions(+), 13 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
> index 7352d3f..cf070fd 100644
> --- a/arch/powerpc/include/asm/mmu-hash64.h
> +++ b/arch/powerpc/include/asm/mmu-hash64.h
> @@ -607,6 +607,9 @@ static inline unsigned long get_kernel_vsid(unsigned long ea, int ssize)
>  	context = (MAX_USER_CONTEXT) + ((ea >> 60) - 0xc) + 1;
>  	return get_vsid(context, ea, ssize);
>  }
> +
> +unsigned htab_shift_for_mem_size(unsigned long mem_size);
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_POWERPC_MMU_HASH64_H_ */
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index fdcf9d1..da5d279 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -611,10 +611,26 @@ static int __init htab_dt_scan_pftsize(unsigned long node,
>  	return 0;
>  }
>  
> -static unsigned long __init htab_get_table_size(void)
> +unsigned htab_shift_for_mem_size(unsigned long mem_size)
>  {
> -	unsigned long mem_size, rnd_mem_size, pteg_count, psize;
> +	unsigned memshift = __ilog2(mem_size);
> +	unsigned pshift = mmu_psize_defs[mmu_virtual_psize].shift;
> +	unsigned pteg_shift;
> +
> +	/* round mem_size up to next power of 2 */
> +	if ((1UL << memshift) < mem_size)
> +		memshift += 1;
> +
> +	/* aim for 2 pages / pteg */
> +	pteg_shift = memshift - (pshift + 1);
> +
> +	/* 2^11 PTEGS / 2^18 bytes is the minimum htab size permitted
> +	 * by the architecture */
> +	return max(pteg_shift + 7, 18U);
> +}
>  
> +static unsigned long __init htab_get_table_size(void)
> +{
>  	/* If hash size isn't already provided by the platform, we try to
>  	 * retrieve it from the device-tree. If it's not there neither, we
>  	 * calculate it now based on the total RAM size
> @@ -624,17 +640,7 @@ static unsigned long __init htab_get_table_size(void)
>  	if (ppc64_pft_size)
>  		return 1UL << ppc64_pft_size;
>  
> -	/* round mem_size up to next power of 2 */
> -	mem_size = memblock_phys_mem_size();
> -	rnd_mem_size = 1UL << __ilog2(mem_size);
> -	if (rnd_mem_size < mem_size)
> -		rnd_mem_size <<= 1;
> -
> -	/* # pages / 2 */
> -	psize = mmu_psize_defs[mmu_virtual_psize].shift;
> -	pteg_count = max(rnd_mem_size >> (psize + 1), 1UL << 11);
> -
> -	return pteg_count << 7;
> +	return 1UL << htab_shift_for_mem_size(memblock_phys_mem_size());
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG
> -- 
> 2.5.0

On Tue, 2016-09-02 at 03:32:43 UTC, David Gibson wrote:
> htab_get_table_size() either retrieve the size of the hash page table (HPT)
> from the device tree - if the HPT size is determined by firmware - or
> uses a heuristic to determine a good size based on RAM size if the kernel
> is responsible for allocating the HPT.
> 
> To support a PAPR extension allowing resizing of the HPT, we're going to
> want the memory size -> HPT size logic elsewhere, so split it out into a
> helper function.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/5c3c7ede2bdcb85fa2fd51c814

I reworded one comment a little, from:

	/* 2^11 PTEGS / 2^18 bytes is the minimum htab size permitted
	 * by the architecture */

to:
	/*
	 * 2^11 PTEGS of 128 bytes each, ie. 2^18 bytes is the minimum htab
	 * size permitted by the architecture.
	 */

To avoid any confusion about the "/" referring to division.

cheers

On Wed, Mar 02, 2016 at 09:21:19AM +1100, Michael Ellerman wrote:
> On Tue, 2016-09-02 at 03:32:43 UTC, David Gibson wrote:
> > htab_get_table_size() either retrieve the size of the hash page table (HPT)
> > from the device tree - if the HPT size is determined by firmware - or
> > uses a heuristic to determine a good size based on RAM size if the kernel
> > is responsible for allocating the HPT.
> > 
> > To support a PAPR extension allowing resizing of the HPT, we're going to
> > want the memory size -> HPT size logic elsewhere, so split it out into a
> > helper function.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> 
> Applied to powerpc next, thanks.
> 
> https://git.kernel.org/powerpc/c/5c3c7ede2bdcb85fa2fd51c814
> 
> I reworded one comment a little, from:
> 
> 	/* 2^11 PTEGS / 2^18 bytes is the minimum htab size permitted
> 	 * by the architecture */
> 
> to:
> 	/*
> 	 * 2^11 PTEGS of 128 bytes each, ie. 2^18 bytes is the minimum htab
> 	 * size permitted by the architecture.
> 	 */
> 
> To avoid any confusion about the "/" referring to division.

Good call, thanks.