Re: [PATCH] Tight check of pfn_valid on sparsemem - v4

Christoph Lameter
2010-08-02T15:48:55Z

On Sat, 31 Jul 2010, Russell King - ARM Linux wrote:

> Looking at vmemmap sparsemem, we need to fix it as the page table
> allocation in there bypasses the arch defined page table setup.

You are required to define your own vmemmap_populate function. In that you
can call some of the provided functions or use your own.

> This causes a problem if you have 256-entry L2 page tables with no
> room for the additional Linux VM PTE support bits (such as young,
> dirty, etc), and need to glue two 256-entry L2 hardware page tables
> plus a Linux version to store its accounting in each page. See
> arch/arm/include/asm/pgalloc.h.
>
> So this causes a problem with vmemmap:
>
> pte_t entry;
> void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node);
> if (!p)
> return NULL;
> entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
>
> Are you willing for this stuff to be replaced by architectures as
> necessary?

Sure its designed that way. If we missed anything we'd surely add it.