Re: [PATCH 13/35] autonuma: add page structure fields

Peter Zijlstra
2012-05-29T13:16:45Z

On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:

> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 780ded7..e8dc82c 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -126,6 +126,31 @@ struct page {
> struct page *first_page; /* Compound tail pages */
> };
>
> +#ifdef CONFIG_AUTONUMA
> + /*
> + * FIXME: move to pgdat section along with the memcg and allocate
> + * at runtime only in presence of a numa system.
> + */
> + /*
> + * To modify autonuma_last_nid lockless the architecture,
> + * needs SMP atomic granularity < sizeof(long), not all archs
> + * have that, notably some alpha. Archs without that requires
> + * autonuma_last_nid to be a long.
> + */
> +#if BITS_PER_LONG > 32
> + int autonuma_migrate_nid;
> + int autonuma_last_nid;
> +#else
> +#if MAX_NUMNODES >= 32768
> +#error "too many nodes"
> +#endif
> + /* FIXME: remember to check the updates are atomic */
> + short autonuma_migrate_nid;
> + short autonuma_last_nid;
> +#endif
> + struct list_head autonuma_migrate_node;
> +#endif
> +
> /*
> * On machines where all RAM is mapped into kernel address space,
> * we can simply calculate the virtual address. On machines with

24 bytes per page.. or ~0.6% of memory gone. This is far too great a
price to pay.

At LSF/MM Rik already suggested you limit the number of pages that can
be migrated concurrently and use this to move the extra list_head out of
struct page and into a smaller amount of extra structures, reducing the
total overhead.