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Message-ID: <2926b360-5204-45f5-e1a0-e260214f8dbf@gmail.com>
Date: Fri, 10 Dec 2021 15:43:56 +0800
From: Eric Ren <renzhengeek@...il.com>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
Michael Ellerman <mpe@...erman.id.au>,
Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
linuxppc-dev@...ts.ozlabs.org,
virtualization@...ts.linux-foundation.org,
iommu@...ts.linux-foundation.org, Vlastimil Babka <vbabka@...e.cz>,
Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [RFC PATCH v2 1/7] mm: page_alloc: avoid merging non-fallbackable
pageblocks with others.
Hi,
On 2021/12/10 07:04, 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.
> Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.
>
> [1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/
>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
> include/linux/mmzone.h | 6 ++++++
> mm/page_alloc.c | 28 ++++++++++++++++++----------
> 2 files changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 58e744b78c2c..b925431b0123 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -83,6 +83,12 @@ static inline bool is_migrate_movable(int mt)
> return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
> }
>
> +/* See fallbacks[MIGRATE_TYPES][3] in page_alloc.c */
> +static inline bool migratetype_has_fallback(int mt)
> +{
> + return mt < MIGRATE_PCPTYPES;
> +}
> +
I would suggest spliting the patch into 2 parts. The first part: no
functioning change, just introduce migratetype_has_fallback()
and replace where it applys to.
> #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 edfd6c81af82..107a5f186d3b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1041,6 +1041,12 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
> return page_is_buddy(higher_page, higher_buddy, order + 1);
> }
>
> +static inline bool has_non_fallback_pageblock(struct zone *zone)
> +{
> + return has_isolate_pageblock(zone) || zone_cma_pages(zone) != 0 ||
> + zone->nr_reserved_highatomic != 0;
Make zone->nr_reserved_highatomic != 0 a helper as zone_cma_pages()?
> +}
> +
> /*
> * Freeing function for a buddy system allocator.
> *
> @@ -1116,14 +1122,15 @@ 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))) {
> + if (unlikely(has_non_fallback_pageblock(zone))) {
I'm not familiar with the code details, just wondering if this change
would has side effects on cma
pageblock merging as it the condition stronger?
Thanks,
Eric
> int buddy_mt;
>
> buddy_pfn = __find_buddy_pfn(pfn, order);
> @@ -1131,8 +1138,8 @@ static inline void __free_one_page(struct page *page,
> buddy_mt = get_pageblock_migratetype(buddy);
>
> if (migratetype != buddy_mt
> - && (is_migrate_isolate(migratetype) ||
> - is_migrate_isolate(buddy_mt)))
> + && (!migratetype_has_fallback(migratetype) ||
> + !migratetype_has_fallback(buddy_mt)))
> goto done_merging;
> }
> max_order = order + 1;
> @@ -2483,6 +2490,7 @@ 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 },
> + [MIGRATE_HIGHATOMIC] = { MIGRATE_TYPES }, /* Never used */
> #ifdef CONFIG_CMA
> [MIGRATE_CMA] = { MIGRATE_TYPES }, /* Never used */
> #endif
> @@ -2794,8 +2802,8 @@ 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 pageblock */
> + if (migratetype_has_fallback(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
> move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
> @@ -3544,8 +3552,8 @@ 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);
> }
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