On Wed, 22 Jun 2016 14:56:17 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 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:
>
And
mm-compaction-split-freepages-without-holding-the-zone-lock-fix.patch
churns things around some more. Now this:
/* Found a free page, will break it into order-0 pages */
order = page_order(page);
isolated = __isolate_free_page(page, order);
set_page_private(page, order);
total_isolated += isolated;
list_add_tail(&page->lru, freelist);
cc->nr_freepages += isolated;
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:
and things are looking a bit better...
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