On Thu, 06 Oct 2011 15:54:44 +0200 Marek Szyprowski m.szyprowski@samsung.com wrote:
From: Michal Nazarewicz m.nazarewicz@samsung.com
The MIGRATE_CMA migration type has two main characteristics: (i) only movable pages can be allocated from MIGRATE_CMA pageblocks and (ii) page allocator will never change migration type of MIGRATE_CMA pageblocks.
This guarantees that page in a MIGRATE_CMA page block can always be migrated somewhere else (unless there's no memory left in the system).
It is designed to be used with Contiguous Memory Allocator (CMA) for allocating big chunks (eg. 10MiB) of physically contiguous memory. Once driver requests contiguous memory, CMA will migrate pages from MIGRATE_CMA pageblocks.
To minimise number of migrations, MIGRATE_CMA migration type is the last type tried when page allocator falls back to other migration types then requested.
...
+#ifdef CONFIG_CMA_MIGRATE_TYPE +# define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA) +#else +# define is_migrate_cma(migratetype) false +#endif
Implement in C, please.
...
--- a/mm/compaction.c +++ b/mm/compaction.c @@ -115,6 +115,16 @@ static bool suitable_migration_target(struct page *page) if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE) return false;
- /* Keep MIGRATE_CMA alone as well. */
- /*
* XXX Revisit. We currently cannot let compaction touch CMA* pages since compaction insists on changing their migration* type to MIGRATE_MOVABLE (see split_free_page() called from* isolate_freepages_block() above).*/
Talk to us about this.
How serious is this shortcoming in practice? What would a fix look like? Is anyone working on an implementation, or planning to do so?
- if (is_migrate_cma(migratetype))
return false;- /* If the page is a large free page, then allow migration */ if (PageBuddy(page) && page_order(page) >= pageblock_order) return true;
...
+void __init init_cma_reserved_pageblock(struct page *page) +{
- struct page *p = page;
- unsigned i = pageblock_nr_pages;
- prefetchw(p);
- do {
if (--i)prefetchw(p + 1);__ClearPageReserved(p);set_page_count(p, 0);- } while (++p, i);
- set_page_refcounted(page);
- set_pageblock_migratetype(page, MIGRATE_CMA);
- __free_pages(page, pageblock_order);
- totalram_pages += pageblock_nr_pages;
+}
I wonder if the prefetches do any good. it doesn't seem very important in an __init function.
+#endif
...