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Date: Thu, 7 May 2015 00:16:18 -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>,
        Christoph Hellwig <hch@infradead.org>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v3 1/4] fs: kiocb: introduce IOCB_DONT_DIRTY_PAGE flag
 for direct IO
Message-ID: <20150507071618.GA7595@infradead.org>
References: <1430932106-17451-1-git-send-email-ming.lei@canonical.com>
 <1430932106-17451-2-git-send-email-ming.lei@canonical.com>
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On Thu, May 07, 2015 at 01:08:23AM +0800, Ming Lei wrote:
> When direct IO is submitted from kernel, it is often unnecessary
> to dirty pages, for example of loop, dirtying pages have been
> considered in the upper filesystem(over loop) side already, and
> they don't need to be dirtied again.
> 
> So this patch introduces IOCB_DONT_DIRTY_PAGE flag for direct IO,
> and other ITER_BVEC and ITER_KVEC cases might benefit from it too.
> 
> The patch is based on previous Dave's patch.

in-kernel I/O should never dirty the pages written to or read from,
so just checking the iov_iter type should be enough.