linux-kernel - Re: [PATCH v2 12/28] mm: Add folio_put

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Message-ID: <f91d9546-1621-8431-5ac7-2192adcf9482@nvidia.com>
Date:   Mon, 10 Jan 2022 20:14:04 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-mm@...ck.org
Cc:     Christoph Hellwig <hch@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v2 12/28] mm: Add folio_put_refs()

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> This is like folio_put(), but puts N references at once instead of
> just one.  It's like put_page_refs(), but does one atomic operation
> instead of two, and is available to more than just gup.c.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>   include/linux/mm.h | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 598be27d4d2e..bf9624ca61c3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1234,6 +1234,26 @@ static inline void folio_put(struct folio *folio)
>   		__put_page(&folio->page);
>   }
>   
> +/**
> + * folio_put_refs - Reduce the reference count on a folio.
> + * @folio: The folio.
> + * @refs: The number of references to reduce.

Tiny rewording suggestion, if you end up sending another version:

  * @refs: The amount to subtract from the folio's reference count.

> + *
> + * If the folio's reference count reaches zero, the memory will be
> + * released back to the page allocator and may be used by another
> + * allocation immediately.  Do not access the memory or the struct folio
> + * after calling folio_put_refs() unless you can be sure that these weren't
> + * the last references.
> + *
> + * Context: May be called in process or interrupt context, but not in NMI
> + * context.  May be called while holding a spinlock.
> + */
> +static inline void folio_put_refs(struct folio *folio, int refs)
> +{
> +	if (folio_ref_sub_and_test(folio, refs))
> +		__put_page(&folio->page);
> +}
> +
>   static inline void put_page(struct page *page)
>   {
>   	struct folio *folio = page_folio(page);


Reviewed-by: John Hubbard <jhubbard@...dia.com>


thanks,
-- 
John Hubbard
NVIDIA