On 09/25/2013 04:14 PM, Srivatsa S. Bhat wrote:
> @@ -605,16 +713,22 @@ static inline void __free_one_page(struct page *page,
> buddy_idx = __find_buddy_index(combined_idx, order + 1);
> higher_buddy = higher_page + (buddy_idx - combined_idx);
> if (page_is_buddy(higher_page, higher_buddy, order + 1)) {
> - list_add_tail(&page->lru,
> - &zone->free_area[order].free_list[migratetype].list);
> +
> + /*
> + * Implementing an add_to_freelist_tail() won't be
> + * very useful because both of them (almost) add to
> + * the tail within the region. So we could potentially
> + * switch off this entire "is next-higher buddy free?"
> + * logic when memory regions are used.
> + */
> + add_to_freelist(page, &area->free_list[migratetype]);
> goto out;
> }
> }
Commit 6dda9d55b says that this had some discrete performance gains.
It's a bummer that this deoptimizes it, and I think that (expected)
performance degredation at least needs to be referenced _somewhere_.
I also find it very hard to take code seriously which stuff like this:
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> + WARN(region->nr_free == 0, "%s: nr_free messed up\n", __func__);
> +#endif
nine times.
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