On Tue, 22 Jan 2013 17:12:41 +0000
Mel Gorman <mgorman@xxxxxxx> wrote:
> From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
>
> page->_last_nid fits into page->flags on 64-bit. The unlikely 32-bit NUMA
> configuration with NUMA Balancing will still need an extra page field.
> As Peter notes "Completely dropping 32bit support for CONFIG_NUMA_BALANCING
> would simplify things, but it would also remove the warning if we grow
> enough 64bit only page-flags to push the last-cpu out."
How much space remains in the 64-bit page->flags?
Was this the best possible use of the remaining space?
It's good that we can undo this later by flipping
LAST_NID_NOT_IN_PAGE_FLAGS.
> [mgorman@xxxxxxx: Minor modifications]
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Several of these patches are missing signoffs (Peter and Hugh).
>
> ...
>
> +static inline int page_last_nid(struct page *page)
> +{
> + return (page->flags >> LAST_NID_PGSHIFT) & LAST_NID_MASK;
> +}
> +
> +static inline int page_xchg_last_nid(struct page *page, int nid)
> +{
> + unsigned long old_flags, flags;
> + int last_nid;
> +
> + do {
> + old_flags = flags = page->flags;
> + last_nid = page_last_nid(page);
> +
> + flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
> + flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
> + } while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
> +
> + return last_nid;
> +}
> +
> +static inline void reset_page_last_nid(struct page *page)
> +{
> + page_xchg_last_nid(page, (1 << LAST_NID_SHIFT) - 1);
> +}
page_xchg_last_nid() and reset_page_last_nid() are getting nuttily
large. Please investigate uninlining them?
reset_page_last_nid() is poorly named. page_reset_last_nid() would be
better, and consistent.
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