linux-kernel - Re: [PATCH mm-unstable v2 1/6] mm: Add folio_estimated

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Message-ID: <477bbc1e-a60a-cfce-d31e-0b4bdd5f6429@redhat.com>
Date:   Wed, 25 Jan 2023 11:20:03 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH mm-unstable v2 1/6] mm: Add folio_estimated_mapcount()

On 24.01.23 02:22, Vishal Moola (Oracle) wrote:
> folio_estimated_mapcount() takes in a folio and calls page_mapcount() on
> the first page of that folio.
> 
> This is necessary for folio conversions where we only care about either the
> entire_mapcount of a large folio, or the mapcount of a not large folio.
> 
> This is in contrast to folio_mapcount() which calculates the total
> number of the times a folio and its subpages are mapped.
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> ---
>   include/linux/mm.h | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c9db257f09b3..543c360f7ecc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -875,6 +875,11 @@ static inline int page_mapcount(struct page *page)
>   	return mapcount;
>   }
>   
> +static inline int folio_estimated_mapcount(struct folio *folio)
> +{
> +	return page_mapcount(folio_page(folio, 0));
> +}
> +
>   int folio_total_mapcount(struct folio *folio);
>   
>   /**

I'm sorry, but "estimated" as absolutely unclear semantics. You could 
have a THP mapped into 9999 processes using THP and the estimation would 
be "0".

Huh? Absolutely unclear and confusing. No thanks.

-- 
Thanks,

David / dhildenb