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Message-ID: <Ye+b6YKiQ6ylEO6M@kernel.org>
Date: Tue, 25 Jan 2022 08:42:49 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Zi Yan <ziy@...dia.com>
Cc: Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, David Hildenbrand <david@...hat.com>,
Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: page_alloc: avoid merging non-fallbackable
pageblocks with others.
On Mon, Jan 24, 2022 at 12:59:57PM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.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.
>
> Remove MIGRARTE_CMA and MIGRATE_ISOLATE from fallbacks list, since they
> are never used.
>
> [1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/
>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Acked-by: Mel Gorman <mgorman@...hsingularity.net>
Acked-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
> include/linux/mmzone.h | 11 +++++++++++
> mm/page_alloc.c | 44 ++++++++++++++++++++----------------------
> 2 files changed, 32 insertions(+), 23 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aed44e9b5d89..71b77aab748d 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -83,6 +83,17 @@ static inline bool is_migrate_movable(int mt)
> return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
> }
>
> +/*
> + * Check whether a migratetype can be merged with another migratetype.
> + *
> + * It is only mergeable when it can fall back to other migratetypes for
> + * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
> + */
> +static inline bool migratetype_is_mergeable(int mt)
> +{
> + return mt < MIGRATE_PCPTYPES;
> +}
> +
> #define for_each_migratetype_order(order, type) \
> for (order = 0; order < MAX_ORDER; order++) \
> for (type = 0; type < MIGRATE_TYPES; type++)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8dd6399bafb5..5a91d4d9279a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1117,25 +1117,24 @@ static inline void __free_one_page(struct page *page,
> }
> if (order < MAX_ORDER - 1) {
> /* If we are here, it means order is >= pageblock_order.
> - * We want to prevent merge between freepages on isolate
> - * pageblock and normal pageblock. Without this, pageblock
> - * isolation could cause incorrect freepage or CMA accounting.
> + * We want to prevent merge between freepages on pageblock
> + * without fallbacks and normal pageblock. Without this,
> + * pageblock isolation could cause incorrect freepage or CMA
> + * accounting or HIGHATOMIC accounting.
> *
> * We don't want to hit this code for the more frequent
> * low-order merging.
> */
> - if (unlikely(has_isolate_pageblock(zone))) {
> - int buddy_mt;
> + int buddy_mt;
>
> - buddy_pfn = __find_buddy_pfn(pfn, order);
> - buddy = page + (buddy_pfn - pfn);
> - buddy_mt = get_pageblock_migratetype(buddy);
> + buddy_pfn = __find_buddy_pfn(pfn, order);
> + buddy = page + (buddy_pfn - pfn);
> + buddy_mt = get_pageblock_migratetype(buddy);
>
> - if (migratetype != buddy_mt
> - && (is_migrate_isolate(migratetype) ||
> - is_migrate_isolate(buddy_mt)))
> - goto done_merging;
> - }
> + if (migratetype != buddy_mt
> + && (!migratetype_is_mergeable(migratetype) ||
> + !migratetype_is_mergeable(buddy_mt)))
> + goto done_merging;
> max_order = order + 1;
> goto continue_merging;
> }
> @@ -2479,17 +2478,13 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
> /*
> * This array describes the order lists are fallen back to when
> * the free lists for the desirable migrate type are depleted
> + *
> + * The other migratetypes do not have fallbacks.
> */
> static int fallbacks[MIGRATE_TYPES][3] = {
> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
> -#ifdef CONFIG_CMA
> - [MIGRATE_CMA] = { MIGRATE_TYPES }, /* Never used */
> -#endif
> -#ifdef CONFIG_MEMORY_ISOLATION
> - [MIGRATE_ISOLATE] = { MIGRATE_TYPES }, /* Never used */
> -#endif
> };
>
> #ifdef CONFIG_CMA
> @@ -2795,8 +2790,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
>
> /* Yoink! */
> mt = get_pageblock_migratetype(page);
> - if (!is_migrate_highatomic(mt) && !is_migrate_isolate(mt)
> - && !is_migrate_cma(mt)) {
> + /* Only reserve normal pageblocks (i.e., they can merge with others) */
> + if (migratetype_is_mergeable(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
> move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
> @@ -3545,8 +3540,11 @@ 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 pageblocks (i.e., they can merge
> + * with others)
> + */
> + if (migratetype_is_mergeable(mt))
> set_pageblock_migratetype(page,
> MIGRATE_MOVABLE);
> }
> --
> 2.34.1
>
--
Sincerely yours,
Mike.
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