On Mon, Jul 07 2014, Andrew Morton <a...@linux-foundation.org> wrote:
> What I proposed is that CMA call invalidate_bh_lrus() right at the
> outset. Something along the lines of
>
> --- a/mm/page_alloc.c~a
> +++ a/mm/page_alloc.c
> @@ -6329,6 +6329,14 @@ int alloc_contig_range(unsigned long sta
> };
> INIT_LIST_HEAD(&cc.migratepages);
>
> +#ifdef CONFIG_CMA
> + /*
> + * Comment goes here
> + */
> + if (migratetype == MIGRATE_CMA)
> + invalidate_bh_lrus();
> +#endif
> +
This seems reasonable, except I think it should go after
start_isolate_page_range call because otherwise there's no guarantee
that someone won't grab those pages back.
Also to avoid the #ifdef perhaps we want this as well:
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 6cbd1b6..2640a55 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -64,10 +64,11 @@ enum {
};
#ifdef CONFIG_CMA
-# define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
+# define __is_migrate_cma(migratetype) ((migratetype) == MIGRATE_CMA)
#else
-# define is_migrate_cma(migratetype) false
+# define __is_migrate_cma(migratetype) false
#endif
+#define is_migrate_cma(migratetype) unlikely(__is_migrate_cma(migratetype))
#define for_each_migratetype_order(order, type) \
for (order = 0; order < MAX_ORDER; order++) \
and then use “if (__is_migrate_cma(migratetype))”.
> /*
> * What we do here is we mark all pageblocks in range as
> * MIGRATE_ISOLATE. Because pageblock and max order pages may
>
>
> - I'd have thought that it would make sense to do this for huge pages
> as well (MIGRATE_MOVABLE) but nobody really seems to know.
>
> - There's a patch floating around ("Allow increasing the buffer-head
> per-CPU LRU size") which will double the size of the bh lrus, so this
> all becomes more important.
>
> - alloc_contig_range() does lru_add_drain_all() and drain_all_pages()
> *after* performing the allocation. I can't work out why this is the
> case and of course it is undocumented. If this is indeed not a bug
> then probably the invalidate_bh_lrus() should happen in the same
> place.
The purpose is to get free non-buddy pages (so pages on PCP lists for
instance) back onto the buddy list. It's safe to move those calls above
the call to __alloc_contig_migrate_range, but I don't think it will
change anything (except of course the fact that if migration fails,
we'll do the draining for nothing).
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +--<m...@google.com>--<xmpp:min...@jabber.org>--ooO--(_)--Ooo--
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