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

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Message-ID: <5695C8C0.1080005@huawei.com>
Date:	Wed, 13 Jan 2016 11:47:12 +0800
From:	"Chenjie (K)" <chenjie6@...wei.com>
To:	Matthew Wilcox <willy@...ux.intel.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


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.

  In our case, we use ext2 filesystem with dax on the reserved mem.
we mmap the file and write some things ,the file is not changed immediately.

this is the wrong place to change that attribute:
	Do you mean
add
	ext4_file_mmap/ext2_file_mmap

	if (IS_DAX(file_inode(file))) {
		vma->vm_ops = &ext4_dax_vm_ops;
		vma->vm_flags |= VM_MIXEDMAP;
+	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
	} else {
like this ???

On 2016/1/12 20:51, Matthew Wilcox wrote:
> On Tue, Jan 12, 2016 at 07:43:45PM +0800, chenjie6@...wei.com wrote:
>> From: chenjie <chenjie6@...wei.com>
>>
>> We show the pte:
>> 	*pte=01600000159c8fd3
>> The page should be no_cache attr,it will be better.
>
> I disagree.  What data do you have to show that the WC attribute would
> be better than WB?
>
> Even if we agree to that, this is the wrong place to change that
> attribute, so the patch is NAKed.  But you need more than "it will
> be better".
>
> .
>