linux-kernel - Re: [PATCH v3 1/4] fs: kiocb: introduce IOCB_DONT_DIRTY

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Date:	Thu, 7 May 2015 00:16:18 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Christoph Hellwig <hch@...radead.org>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v3 1/4] fs: kiocb: introduce IOCB_DONT_DIRTY_PAGE flag
 for direct IO

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.
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