linux-kernel - Re: [PATCH v4 1/5] fs: kiocb: introduce IOCB_DONT_DIRTY

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Date:	Sat, 6 Jun 2015 08:42:33 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	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>, Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v4 1/5] fs: kiocb: introduce IOCB_DONT_DIRTY_PAGE flag for
 direct IO

On Fri, Jun 5, 2015 at 11:03 PM, Christoph Hellwig <hch@...radead.org> wrote:
> 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.

Both ITER_KVEC and ITER_BVEC doesn't mean the pages are kernel
page, for example of loop and swap. That is why this patch is more flexiable,
and won't cause regression since the users may have different dirtying
rules as you mentioned last time.

http://marc.info/?t=143093223200001&r=1&w=2

Thanks,
Ming
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