Re: [RFC PATCH v3 1/8] mm: page_alloc: avoid merging non-fallbackable pageblocks with others.

On 13.01.22 12:36, Mike Rapoport wrote:

On Wed, Jan 12, 2022 at 11:54:49AM +0100, David Hildenbrand wrote:

quoted

On 05.01.22 22:47, Zi Yan wrote:

quoted

From: Zi Yan <ziy@nvidia.com>

This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.
It prepares for the upcoming removal of the MAX_ORDER-1 alignment
requirement for CMA and alloc_contig_range().

MIGRARTE_HIGHATOMIC should not merge with other migratetypes like
MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.
Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.

[1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/ (local)

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/mmzone.h |  6 ++++++
 mm/page_alloc.c        | 28 ++++++++++++++++++----------
 2 files changed, 24 insertions(+), 10 deletions(-)

...

quoted

quoted

@@ -3545,8 +3553,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
 		struct page *endpage = page + (1 << order) - 1;
 		for (; page < endpage; page += pageblock_nr_pages) {
 			int mt = get_pageblock_migratetype(page);
-			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
-			    && !is_migrate_highatomic(mt))
+			/* Only change normal pageblock */
+			if (migratetype_has_fallback(mt))
 				set_pageblock_migratetype(page,
 							  MIGRATE_MOVABLE);
 		}

That part is a nice cleanup IMHO. Although the "has fallback" part is a
bit imprecise. "migratetype_is_mergable()" might be a bit clearer.
ideally "migratetype_is_mergable_with_other_types()". Can we come up
with a nice name for that?

migratetype_is_mergable() kinda implies "_with_other_types", no?

I like migratetype_is_mergable() more than _has_fallback().

My $0.02 to bikeshedding :)

:)

Yeah, for me migratetype_is_mergable() would also be good enough. I
think I was at first thinking one could mistake it with a dedicated
migratetype. But such functions are historically called

is_migrate_cma/is_migrate_cma/....

-- 
Thanks,

David / dhildenb