On Wed, Aug 15, 2012 at 02:47:00PM +0100, Arnd Bergmann wrote:

On Tuesday 14 August 2012, Catalin Marinas wrote:

quoted

+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	pgd_t *new_pgd;
+
+	new_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL, PGD_ORDER);
+	if (!new_pgd)
+		return NULL;
+
+	memset(new_pgd, 0, PAGE_SIZE << PGD_ORDER);
+
+	return new_pgd;
+}
+
+void pgd_free(struct mm_struct *mm, pgd_t *pgd)
+{
+	free_pages((unsigned long)pgd, PGD_ORDER);
+}

 
According to the documentation, you should only need 8kb for the pgd on
a 64kb page system. Is it required that you use up a full page here?

Not with the current virtual memory layout with 39-bit address space for
kernel. With 64K pages we can increase the address space to 42-bit while
still using 2-level page table, in which case a full page is used.

But for now I'll keep the same virtual memory layout and add a check on
(PTRS_PER_PGD * sizeof(pgd_t)), the compiler will choose the right path.

-- 
Catalin