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/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 335cd41..90dd928 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -609,10 +609,28 @@
return 0;
}
+unsigned htab_shift_for_mem_size(unsigned long mem_size)
+{
+ 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)
{
- unsigned long mem_size, rnd_mem_size, pteg_count, psize;
-
/* 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 @@
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