On Tue, 21 Jun 2016 18:22:49 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> If the memory compaction free scanner cannot successfully split a free
> page (only possible due to per-zone low watermark), terminate the free
> scanner rather than continuing to scan memory needlessly. If the
> watermark is insufficient for a free page of order <= cc->order, then
> terminate the scanner since all future splits will also likely fail.
>
> This prevents the compaction freeing scanner from scanning all memory on
> very large zones (very noticeable for zones > 128GB, for instance) when
> all splits will likely fail while holding zone->lock.
>
This collides pretty heavily with Joonsoo's "mm/compaction: split
freepages without holding the zone lock".
I ended up with this, in isolate_freepages_block():
/* Found a free page, will break it into order-0 pages */
order = page_order(page);
isolated = __isolate_free_page(page, page_order(page));
set_page_private(page, order);
total_isolated += isolated;
cc->nr_freepages += isolated;
list_add_tail(&page->lru, freelist);
if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
blockpfn += isolated;
break;
}
/* Advance to the end of split page */
blockpfn += isolated - 1;
cursor += isolated - 1;
continue;
isolate_fail:
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