linux-kernel - Re: [PATCH v2] mm: huge_memory: convert split_huge_pages

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Date:   Fri, 30 Dec 2022 13:45:35 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <willy@...radead.org>
Subject: Re: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to
 use a folio

On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:

> Straightforwardly convert split_huge_pages_all() to use a folio.
> 
> ...
>
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2932,6 +2932,7 @@ static void split_huge_pages_all(void)
>  {
>  	struct zone *zone;
>  	struct page *page;
> +	struct folio *folio;
>  	unsigned long pfn, max_zone_pfn;
>  	unsigned long total = 0, split = 0;
>  
> @@ -2944,24 +2945,32 @@ static void split_huge_pages_all(void)
>  			int nr_pages;
>  
>  			page = pfn_to_online_page(pfn);
> -			if (!page || !get_page_unless_zero(page))
> +			if (!page || PageTail(page))
> +				continue;
> +			folio = page_folio(page);
> +			if (!folio_try_get(folio))
>  				continue;
>  
> -			if (zone != page_zone(page))
> +			if (unlikely(page_folio(page) != folio))
> +				goto next;
> +
> +			if (zone != folio_zone(folio))
>  				goto next;

I'm still not understanding the above hunk.  Why is the
"page_folio(page) != folio" check added?  Should it be commented?


> -			if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
> +			if (!folio_test_large(folio) ||
> +			    folio_test_hugetlb(folio) ||
> +			    !folio_test_lru(folio))
>  				goto next;
>  
>  			total++;
> -			lock_page(page);
> -			nr_pages = thp_nr_pages(page);
> -			if (!split_huge_page(page))
> +			folio_lock(folio);
> +			nr_pages = folio_nr_pages(folio);
> +			if (!split_folio(folio))
>  				split++;
>  			pfn += nr_pages - 1;
> -			unlock_page(page);
> +			folio_unlock(folio);
>  next:
> -			put_page(page);
> +			folio_put(folio);
>  			cond_resched();
>  		}
>  	}
> -- 
> 2.35.3