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Date:   Sat, 27 Aug 2022 17:12:20 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
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        "Darrick J . Wong" <djwong@kernel.org>,
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Subject: Re: [PATCH 2/6] block: add dio_w_*() wrappers for pin, unpin user
 pages
Message-Id: <20220827171220.fa2f21f6b22c6d3047857381@linux-foundation.org>
In-Reply-To: <4c6903d4-0612-5097-0005-4a9420890826@nvidia.com>
References: <20220827083607.2345453-1-jhubbard@nvidia.com>
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        <20220827152745.3dcd05e98b3a4383af650a72@linux-foundation.org>
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On Sat, 27 Aug 2022 16:59:32 -0700 John Hubbard <jhubbard@nvidia.com> wrote:

> Anyway, I'll change my patch locally for now, to this:
> 
> static inline void dio_w_unpin_user_pages(struct page **pages,
> 					  unsigned long npages)
> {
> 	/* Careful, release_pages() uses a smaller integer type for npages: */
> 	if (WARN_ON_ONCE(npages > (unsigned long)INT_MAX))
> 		return;
> 
> 	release_pages(pages, (int)npages);
> }

Well, it might be slower.  release_pages() has a ton of fluff.

As mentioned, the above might be faster if the pages tend
to have page_count()==1??