linux-kernel - Re: [PATCH] bugfix dax fault page should be no cache

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Message-ID: <20160113163206.GE8945@linux.intel.com>
Date:	Wed, 13 Jan 2016 11:32:06 -0500
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	"Chenjie (K)" <chenjie6@...wei.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, zhihui.gao@...wei.com,
	linux-kernel@...r.kernel.org, lizefan@...wei.com,
	stable@...r.kernel.org
Subject: Re: [PATCH] bugfix dax fault page should be no cache

On Wed, Jan 13, 2016 at 11:47:12AM +0800, Chenjie (K) wrote:
> The DAX means Direct Access for files，if the pages have cache,
> the file is not direct access. But in normal condition,
> we can not find the problem directly.

The file absolutely is direct accessed.  The CPU cache is critical to
performance, and should not be bypassed lightly.  We have instructions to
flush the cache, and a library (see http://pmem.io/) so that applications
don't have to use them directly.