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Date: Fri, 5 Jun 2015 08:03:48 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Ming Lei <ming.lei@canonical.com>
Cc: linux-kernel@vger.kernel.org, Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jens Axboe <axboe@kernel.dk>, Zach Brown <zab@zabbo.net>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>, Tejun Heo <tj@kernel.org>,
        Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH v4 1/5] fs: kiocb: introduce IOCB_DONT_DIRTY_PAGE flag
 for direct IO
Message-ID: <20150605150348.GA6835@infradead.org>
References: <1432881338-898-1-git-send-email-ming.lei@canonical.com>
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As mentioned last time a big fat NAK for this one.  We generally
do not dirty kernel pages anywhere, so a flag that must alway be set
for default behavior just to prepare for a highy hypothetical user that
in the future might want to abuse the interface is a no-go.

Just make the dirtying behavior dependent on the iov_iter type:
dirty for ITER_IOVEC and do nothing for ITER_KVEC and ITER_BVEC.