Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 25 Aug 2020 02:54:28 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, Jeff Layton <jlayton@kernel.org>,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, ceph-devel@vger.kernel.org,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast()
Message-ID: <20200825015428.GU1236603@ZenIV.linux.org.uk>
References: <20200822042059.1805541-1-jhubbard@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200822042059.1805541-1-jhubbard@nvidia.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote:

> Direct IO behavior:
> 
>     ITER_IOVEC:
>         pin_user_pages_fast();
>         break;
> 
>     ITER_KVEC:    // already elevated page refcount, leave alone
>     ITER_BVEC:    // already elevated page refcount, leave alone
>     ITER_PIPE:    // just, no :)

Why?  What's wrong with splice to O_DIRECT file?