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

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Date:	Mon, 11 May 2015 00:19:09 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	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 08:12:31PM +0800, Ming Lei wrote:
> In case of loop, it is quite specific about dirtying READ pages in
> direct IO because fs over loop has considered dirtying these pages
> already.
> 
> For other cases of ITER_BVEC or ITER_KVEC, if the page is
> anonymous or mapped, dirtying is still needed, otherwise
> the new written data may be dropped like direct-io from user space.

But those would be user pages.  Anyone who passes a kernel page doesn't
expect it do be dirtied for normal kernel interfaces.
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