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Date:   Sun, 26 Apr 2020 22:52:55 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        hch@infradead.org, david@fromorbit.com, willy@infradead.org,
        Andrew Morton <akpm@linux-foundation.org>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        William Kucharski <william.kucharski@oracle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [RFC PATCH 1/9] include/linux/pagemap.h: introduce
 set/clear_fs_page_private
Message-ID: <20200427055255.GA16709@infradead.org>
References: <20200426214925.10970-1-guoqing.jiang@cloud.ionos.com>
 <20200426214925.10970-2-guoqing.jiang@cloud.ionos.com>
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Why not attach_page_private and clear_page_private as that conveys
the use case a little better?

> +static inline void *set_fs_page_private(struct page *page, void *data)
> +{
> +	get_page(page);
> +	set_page_private(page, (unsigned long)data);
> +	SetPagePrivate(page);
> +
> +	return data;
> +}
> +
> +static inline void *clear_fs_page_private(struct page *page)
> +{
> +	void *data = (void *)page_private(page);
> +
> +	if (!PagePrivate(page))
> +		return NULL;
> +	ClearPagePrivate(page);
> +	set_page_private(page, 0);
> +	put_page(page);
> +
> +	return data;
> +}

Can you add kerneldoc comments describing them, including why we
take the refernces?  Also what is the point of the return value
of set_fs_page_private?