On Mon, 12 Nov 2012 09:59:42 +0100 Marek Szyprowski <[email protected]> wrote:
> It has been observed that system tends to keep a lot of CMA free pages > even in very high memory pressure use cases. The CMA fallback for movable > pages is used very rarely, only when system is completely pruned from > MOVABLE pages, what usually means that the out-of-memory even will be > triggered very soon. To avoid such situation and make better use of CMA > pages, a heuristics is introduced which turns on CMA fallback for movable > pages when the real number of free pages (excluding CMA free pages) > approaches low water mark. > > Signed-off-by: Marek Szyprowski <[email protected]> > Reviewed-by: Kyungmin Park <[email protected]> > CC: Michal Nazarewicz <[email protected]> > --- > mm/page_alloc.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index fcb9719..90b51f3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1076,6 +1076,15 @@ static struct page *__rmqueue(struct zone *zone, > unsigned int order, > { > struct page *page; > > +#ifdef CONFIG_CMA > + unsigned long nr_free = zone_page_state(zone, NR_FREE_PAGES); > + unsigned long nr_cma_free = zone_page_state(zone, NR_FREE_CMA_PAGES); > + > + if (migratetype == MIGRATE_MOVABLE && nr_cma_free && > + nr_free - nr_cma_free < 2 * low_wmark_pages(zone)) > + migratetype = MIGRATE_CMA; > +#endif /* CONFIG_CMA */ > + > retry_reserve: > page = __rmqueue_smallest(zone, order, migratetype); erk, this is right on the page allocator hotpath. Bad. At the very least, we could code it so it is not quite so dreadfully inefficient: if (migratetype == MIGRATE_MOVABLE) { unsigned long nr_cma_free; nr_cma_free = zone_page_state(zone, NR_FREE_CMA_PAGES); if (nr_cma_free) { unsigned long nr_free; nr_free = zone_page_state(zone, NR_FREE_PAGES); if (nr_free - nr_cma_free < 2 * low_wmark_pages(zone)) migratetype = MIGRATE_CMA; } } but it still looks pretty bad. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
