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Message-ID: <a2a2180c-62ac-452f-0737-26f01f228c79@linux.dev>
Date:   Sun, 30 Jul 2023 19:01:26 +0800
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Subject: Re: [PATCH 03/13] scatterlist: Add sg_set_folio()
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>
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        linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        netdev@vger.kernel.org
References: <20230621164557.3510324-1-willy@infradead.org>
 <20230621164557.3510324-4-willy@infradead.org>
From:   Zhu Yanjun <yanjun.zhu@linux.dev>
In-Reply-To: <20230621164557.3510324-4-willy@infradead.org>
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在 2023/6/22 0:45, Matthew Wilcox (Oracle) 写道:
> This wrapper for sg_set_page() lets drivers add folios to a scatterlist
> more easily.  We could, perhaps, do better by using a different page
> in the folio if offset is larger than UINT_MAX, but let's hope we get
> a better data structure than this before we need to care about such
> large folios.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   include/linux/scatterlist.h | 24 ++++++++++++++++++++++++
>   1 file changed, 24 insertions(+)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index ec46d8e8e49d..77df3d7b18a6 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -141,6 +141,30 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
>   	sg->length = len;
>   }
>   
> +/**
> + * sg_set_folio - Set sg entry to point at given folio
> + * @sg:		 SG entry
> + * @folio:	 The folio
> + * @len:	 Length of data
> + * @offset:	 Offset into folio
> + *
> + * Description:
> + *   Use this function to set an sg entry pointing at a folio, never assign
> + *   the folio directly. We encode sg table information in the lower bits
> + *   of the folio pointer. See sg_page() for looking up the page belonging
> + *   to an sg entry.
> + *
> + **/
> +static inline void sg_set_folio(struct scatterlist *sg, struct folio *folio,
> +			       size_t len, size_t offset)
> +{
> +	WARN_ON_ONCE(len > UINT_MAX);
> +	WARN_ON_ONCE(offset > UINT_MAX);
> +	sg_assign_page(sg, &folio->page);
> +	sg->offset = offset;
> +	sg->length = len;
> +}
> +

https://elixir.bootlin.com/linux/latest/source/lib/scatterlist.c#L451

Does the following function have folio version?

"
int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
		struct page **pages, unsigned int n_pages, unsigned int offset,
		unsigned long size, unsigned int max_segment,
		unsigned int left_pages, gfp_t gfp_mask)
"

Thanks a lot.
Zhu Yanjun

>   static inline struct page *sg_page(struct scatterlist *sg)
>   {
>   #ifdef CONFIG_DEBUG_SG