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Date:   Tue, 12 Apr 2022 15:10:12 +0200
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To:     Zi Yan <ziy@nvidia.com>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>,
        Eric Ren <renzhengeek@gmail.com>,
        Mike Rapoport <rppt@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
References: <20220406151858.3149821-1-zi.yan@sent.com>
 <20220406151858.3149821-3-zi.yan@sent.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH v10 2/5] mm: page_isolation: check specified range for
 unmovable pages
In-Reply-To: <20220406151858.3149821-3-zi.yan@sent.com>
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On 06.04.22 17:18, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> Enable set_migratetype_isolate() to check specified sub-range for
> unmovable pages during isolation. Page isolation is done
> at MAX_ORDER_NR_PAEGS 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@nvidia.com>
> ---

[...]

>  /*
> - * This function checks whether pageblock includes unmovable pages or not.
> + * This function checks whether the range [start_pfn, end_pfn) includes
> + * unmovable pages or not. The range must fall into a single pageblock and
> + * consequently belong to a single zone.
>   *
>   * PageLRU check without isolation or lru_lock could race so that
>   * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
> @@ -28,12 +30,14 @@
>   * cannot get removed (e.g., via memory unplug) concurrently.
>   *
>   */
> -static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> -				 int migratetype, int flags)
> +static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long end_pfn,
> +				int migratetype, int flags)
>  {
> -	unsigned long iter = 0;
> -	unsigned long pfn = page_to_pfn(page);
> -	unsigned long offset = pfn % pageblock_nr_pages;
> +	unsigned long pfn = start_pfn;
> +	struct page *page = pfn_to_page(pfn);


Just do

struct page *page = pfn_to_page(start_pfn);
struct zone *zone = page_zone(page);

here. No need to lookup the zone again in the loop because, as you
document "must ... belong to a single zone.".

Then, there is also no need to initialize "pfn" here. In the loop header
is sufficient.

> +
> +	VM_BUG_ON(ALIGN_DOWN(start_pfn, pageblock_nr_pages) !=
> +		  ALIGN_DOWN(end_pfn - 1, pageblock_nr_pages));
>  
>  	if (is_migrate_cma_page(page)) {
>  		/*
> @@ -47,8 +51,11 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		return page;
>  	}
>  
> -	for (; iter < pageblock_nr_pages - offset; iter++) {
> -		page = pfn_to_page(pfn + iter);
> +	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> +		struct zone *zone;
> +
> +		page = pfn_to_page(pfn);
> +		zone = page_zone(page);
>  
>  		/*
>  		 * Both, bootmem allocations and memory holes are marked
> @@ -85,7 +92,7 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  			}
>  
>  			skip_pages = compound_nr(head) - (page - head);
> -			iter += skip_pages - 1;
> +			pfn += skip_pages - 1;
>  			continue;
>  		}
>  
> @@ -97,7 +104,7 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		 */
>  		if (!page_ref_count(page)) {
>  			if (PageBuddy(page))
> -				iter += (1 << buddy_order(page)) - 1;
> +				pfn += (1 << buddy_order(page)) - 1;
>  			continue;
>  		}
>  
> @@ -134,11 +141,18 @@ static struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  	return NULL;
>  }
>  
> -static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags)
> +/*
> + * This function set pageblock migratetype to isolate if no unmovable page is
> + * present in [start_pfn, end_pfn). The pageblock must intersect with
> + * [start_pfn, end_pfn).
> + */
> +static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags,
> +			unsigned long start_pfn, unsigned long end_pfn)

I think we might be able do better, eventually not passing start_pfn at
all. Hmm.

I think we want to pull out the
start_isolate_page_range()/undo_isolate_page_range() interface change
into a separate patch.

Let me try to give it a shot, I'll try hacking something up real quick
to see if we can do better.

-- 
Thanks,

David / dhildenb