powerpc/mm/book(e)(3s)/64: Add page table accounting

Introduce a helper pgtable_gfp_flags() which
just returns the current gfp flags and adds
__GFP_ACCOUNT to account for page table allocation.
The generic helper is added to include/asm/pgalloc.h
and has two variants - WARNING ugly bits ahead

1. If the header is included from a module, no check
for mm == &init_mm is done, since init_mm is not
exported
2. For kernel includes, the check is done and required
see (3e79ec7 arch: x86: charge page tables to kmemcg)

The fundamental assumption is that no module should be
doing pgd/pud/pmd and pte alloc's on behalf of init_mm
directly.

NOTE: This adds an overhead to pmd/pud/pgd allocations
similar to x86.  The other alternative was to implement
pmd_alloc_kernel/pud_alloc_kernel and pgd_alloc_kernel
with their offset variants.

For 4k page size, pte_alloc_one no longer calls
pte_alloc_one_kernel.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/pgalloc.h

@@ -3,6 +3,20 @@
 
 #include <linux/mm.h>
 
+#ifndef MODULE
+static inline gfp_t pgtable_gfp_flags(struct mm_struct *mm, gfp_t gfp)
+{
+	if (unlikely(mm == &init_mm))
+		return gfp;
+	return gfp | __GFP_ACCOUNT;
+}
+#else /* !MODULE */
+static inline gfp_t pgtable_gfp_flags(struct mm_struct *mm, gfp_t gfp)
+{
+	return gfp | __GFP_ACCOUNT;
+}
+#endif /* MODULE */
+
 #ifdef CONFIG_PPC_BOOK3S
 #include <asm/book3s/pgalloc.h>
 #else