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>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
index e36dc90..0cea480 100644 (file)
--- a/arch/powerpc/include/asm/mmu-hash64.h
+++ b/arch/powerpc/include/asm/mmu-hash64.h
@@ -608,6 +608,9 @@ 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 335cd41..90dd928 100644 (file)
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -609,10 +609,28 @@ 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 of 128 bytes each, ie. 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
@@ -622,17 +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