[POWERPC] vmemmap fixes to use smaller pages

This changes vmemmap to use a different region (region 0xf) of the
address space, and to configure the page size of that region
dynamically at boot.

The problem with the current approach of always using 16M pages is that
it's not well suited to machines that have small amounts of memory such
as small partitions on pseries, or PS3's.

In fact, on the PS3, failure to allocate the 16M page backing vmmemmap
tends to prevent hotplugging the HV's "additional" memory, thus limiting
the available memory even more, from my experience down to something
like 80M total, which makes it really not very useable.

The logic used by my match to choose the vmemmap page size is:

 - If 16M pages are available and there's 1G or more RAM at boot,
   use that size.
 - Else if 64K pages are available, use that
 - Else use 4K pages

I've tested on a POWER6 (16M pages) and on an iSeries POWER3 (4K pages)
and it seems to work fine.

Note that I intend to change the way we organize the kernel regions &
SLBs so the actual region will change from 0xf back to something else at
one point, as I simplify the SLB miss handler, but that will be for a
later patch.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 26 insertions, 2 deletions

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 2b5a399..0f2d239 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -94,6 +94,9 @@ unsigned long htab_hash_mask;
 int mmu_linear_psize = MMU_PAGE_4K;
 int mmu_virtual_psize = MMU_PAGE_4K;
 int mmu_vmalloc_psize = MMU_PAGE_4K;
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+int mmu_vmemmap_psize = MMU_PAGE_4K;
+#endif
 int mmu_io_psize = MMU_PAGE_4K;
 int mmu_kernel_ssize = MMU_SEGSIZE_256M;
 int mmu_highuser_ssize = MMU_SEGSIZE_256M;
@@ -387,11 +390,32 @@ static void __init htab_init_page_sizes(void)
 	}
 #endif /* CONFIG_PPC_64K_PAGES */
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	/* We try to use 16M pages for vmemmap if that is supported
+	 * and we have at least 1G of RAM at boot
+	 */
+	if (mmu_psize_defs[MMU_PAGE_16M].shift &&
+	    lmb_phys_mem_size() >= 0x40000000)
+		mmu_vmemmap_psize = MMU_PAGE_16M;
+	else if (mmu_psize_defs[MMU_PAGE_64K].shift)
+		mmu_vmemmap_psize = MMU_PAGE_64K;
+	else
+		mmu_vmemmap_psize = MMU_PAGE_4K;
+#endif /* CONFIG_SPARSEMEM_VMEMMAP */
+
 	printk(KERN_DEBUG "Page orders: linear mapping = %d, "
-	       "virtual = %d, io = %d\n",
+	       "virtual = %d, io = %d"
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	       ", vmemmap = %d"
+#endif
+	       "\n",
 	       mmu_psize_defs[mmu_linear_psize].shift,
 	       mmu_psize_defs[mmu_virtual_psize].shift,
-	       mmu_psize_defs[mmu_io_psize].shift);
+	       mmu_psize_defs[mmu_io_psize].shift
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	       ,mmu_psize_defs[mmu_vmemmap_psize].shift
+#endif
+	       );
 
 #ifdef CONFIG_HUGETLB_PAGE
 	/* Init large page size. Currently, we pick 16M or 1M depending