Re: [PATCH v6 2/9] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap()

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Yin Fengwei <fengwei.yin@intel.com>,
	David Hildenbrand <david@redhat.com>, Yu Zhao <yuzhao@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Yang Shi <shy828301@gmail.com>,
	"Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Itaru Kitayama <itaru.kitayama@gmail.com>,
	John Hubbard <jhubbard@nvidia.com>,
	David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 2/9] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap()
Date: Fri, 29 Sep 2023 16:45:24 +0300	[thread overview]
Message-ID: <20230929134524.wwyykrxfikhle54k@box.shutemov.name> (raw)
In-Reply-To: <20230929114421.3761121-3-ryan.roberts@arm.com>

On Fri, Sep 29, 2023 at 12:44:13PM +0100, Ryan Roberts wrote:
> In preparation for anonymous large folio support, improve
> folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be
> passed to it. In this case, all contained pages are accounted using the
> order-0 folio (or base page) scheme.
> 
> Reviewed-by: Yu Zhao <yuzhao@google.com>
> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  mm/rmap.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 8600bd029acf..106149690366 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1266,31 +1266,44 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
>   * This means the inc-and-test can be bypassed.
>   * The folio does not have to be locked.
>   *
> - * If the folio is large, it is accounted as a THP.  As the folio
> + * If the folio is pmd-mappable, it is accounted as a THP.  As the folio
>   * is new, it's assumed to be mapped exclusively by a single process.
>   */
>  void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>  		unsigned long address)
>  {
> -	int nr;
> +	int nr = folio_nr_pages(folio);
>  
> -	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
> +	VM_BUG_ON_VMA(address < vma->vm_start ||
> +			address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
>  	__folio_set_swapbacked(folio);
>  
> -	if (likely(!folio_test_pmd_mappable(folio))) {
> +	if (likely(!folio_test_large(folio))) {
>  		/* increment count (starts at -1) */
>  		atomic_set(&folio->_mapcount, 0);
> -		nr = 1;
> +		__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
> +	} else if (!folio_test_pmd_mappable(folio)) {
> +		int i;
> +
> +		for (i = 0; i < nr; i++) {
> +			struct page *page = folio_page(folio, i);
> +
> +			/* increment count (starts at -1) */
> +			atomic_set(&page->_mapcount, 0);
> +			__page_set_anon_rmap(folio, page, vma,
> +					address + (i << PAGE_SHIFT), 1);
> +		}
> +
> +		atomic_set(&folio->_nr_pages_mapped, nr);

This code should work for !folio_test_large() case too, no?

>  	} else {
>  		/* increment count (starts at -1) */
>  		atomic_set(&folio->_entire_mapcount, 0);
>  		atomic_set(&folio->_nr_pages_mapped, COMPOUND_MAPPED);
> -		nr = folio_nr_pages(folio);
> +		__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>  		__lruvec_stat_mod_folio(folio, NR_ANON_THPS, nr);
>  	}
>  
>  	__lruvec_stat_mod_folio(folio, NR_ANON_MAPPED, nr);
> -	__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>  }
>  
>  /**
> -- 
> 2.25.1
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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