linux-kernel - Re: [PATCH v7 2/5] mm: page_isolation: check specified range for unmovable pages

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Date:   Mon, 14 Mar 2022 18:13:57 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v7 2/5] mm: page_isolation: check specified range for
 unmovable pages

On 11.03.22 19:36, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> Enable set_migratetype_isolate() to check specified sub-range for
> unmovable pages during isolation. Page isolation is done
> at max(MAX_ORDER_NR_PAEGS, pageblock_nr_pages) granularity, but not all
> pages within that granularity are intended to be isolated. For example,
> alloc_contig_range(), which uses page isolation, allows ranges without
> alignment. This commit makes unmovable page check only look for
> interesting pages, so that page isolation can succeed for any
> non-overlapping ranges.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>  include/linux/page-isolation.h | 10 ++++++++
>  mm/page_alloc.c                | 13 +---------
>  mm/page_isolation.c            | 47 +++++++++++++++++++++-------------
>  3 files changed, 40 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index e14eddf6741a..eb4a208fe907 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -15,6 +15,16 @@ static inline bool is_migrate_isolate(int migratetype)
>  {
>  	return migratetype == MIGRATE_ISOLATE;
>  }
> +static inline unsigned long pfn_max_align_down(unsigned long pfn)
> +{
> +	return ALIGN_DOWN(pfn, MAX_ORDER_NR_PAGES);
> +}
> +
> +static inline unsigned long pfn_max_align_up(unsigned long pfn)
> +{
> +	return ALIGN(pfn, MAX_ORDER_NR_PAGES);
> +}
> +
>  #else
>  static inline bool has_isolate_pageblock(struct zone *zone)
>  {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6de57d058d3d..680580a40a35 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8937,16 +8937,6 @@ void *__init alloc_large_system_hash(const char *tablename,
>  }
>  
>  #ifdef CONFIG_CONTIG_ALLOC
> -static unsigned long pfn_max_align_down(unsigned long pfn)
> -{
> -	return ALIGN_DOWN(pfn, MAX_ORDER_NR_PAGES);
> -}
> -
> -static unsigned long pfn_max_align_up(unsigned long pfn)
> -{
> -	return ALIGN(pfn, MAX_ORDER_NR_PAGES);
> -}
> -
>  #if defined(CONFIG_DYNAMIC_DEBUG) || \
>  	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
>  /* Usage: See admin-guide/dynamic-debug-howto.rst */
> @@ -9091,8 +9081,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  	 * put back to page allocator so that buddy can use them.
>  	 */
>  
> -	ret = start_isolate_page_range(pfn_max_align_down(start),
> -				       pfn_max_align_up(end), migratetype, 0);
> +	ret = start_isolate_page_range(start, end, migratetype, 0);
>  	if (ret)
>  		return ret;
>  
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index b34f1310aeaa..e0afc3ee8cf9 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -16,7 +16,8 @@
>  #include <trace/events/page_isolation.h>
>  
>  /*
> - * This function checks whether pageblock includes unmovable pages or not.
> + * This function checks whether pageblock within [start_pfn, end_pfn) includes
> + * unmovable pages or not.
>   *
>   * PageLRU check without isolation or lru_lock could race so that
>   * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
> @@ -29,11 +30,14 @@
>   *
>   */
>  static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> -				 int migratetype, int flags)
> +				 int migratetype, int flags,
> +				 unsigned long start_pfn, unsigned long end_pfn)
>  {
> -	unsigned long iter = 0;
> -	unsigned long pfn = page_to_pfn(page);
> -	unsigned long offset = pfn % pageblock_nr_pages;
> +	unsigned long first_pfn = max(page_to_pfn(page), start_pfn);
> +	unsigned long pfn = first_pfn;
> +	unsigned long last_pfn = min(ALIGN(pfn + 1, pageblock_nr_pages), end_pfn);
> +
> +	page = pfn_to_page(pfn);

I think we should get rid of the page argument completely. The caller
should pass in a reasonable [start_pfn, end_pfn) range, and to any
necessary fixups to the range outside of this function.

The goal should be to have

pfn = start_pfn

and replacing last_pfn by end_pfn.


Ideally we'd end up with "This function checks whether the range
[start_pfn, end_pfn) contains unmovable pages or not."


What would be missing to achieve that?

-- 
Thanks,

David / dhildenb