Re: page table lock patch V15 [0/7]: overview

Nick Piggin
2005-01-13T00:10:08Z

Christoph Lameter wrote:
> On Thu, 13 Jan 2005, Nick Piggin wrote:
>
>
>>Note that this was with my ptl removal patches. I can't see why Christoph's
>>would have _any_ extra overhead as they are, but it looks to me like they're
>>lacking in atomic ops. So I'd expect something similar for Christoph's when
>>they're properly atomic.
>
>
> Pointer operations and word size operations are atomic. So this is mostly
> okay.
>
> The issue arises on architectures that have a large pte size than the
> wordsize. This is only on i386 PAE mode and S/390. S/390 falls back to
> the page table lock for these operations. PAE mode should do the same and
> not use atomic ops if they cannot be made to work in a reasonable manner.
>

Yep well you should be OK then. Your implementation has the advantage
that it only instantiates previously clear ptes... hmm, no I'm wrong,
your ptep_set_access_flags path modifies an existing pte. I think this
can cause subtle races in copy_page_range, and maybe other places,
can't it?