Re: [RFC PATCH 3/3] fuse: add per-file DAX flag

From: JeffleXu <jefflexu@linux.alibaba.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: linux-fsdevel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Liu Bo <bo.liu@linux.alibaba.com>,
	stefanha@redhat.com, miklos@szeredi.hu
Subject: Re: [RFC PATCH 3/3] fuse: add per-file DAX flag
Date: Fri, 16 Jul 2021 09:59:24 +0800	[thread overview]
Message-ID: <bfde6c40-4b67-fd24-0df1-21f0cf5a8fd1@linux.alibaba.com> (raw)
In-Reply-To: <YPDhv0JJHqbMCyXD@redhat.com>

On 7/16/21 9:32 AM, Vivek Goyal wrote:
> On Fri, Jul 16, 2021 at 09:18:34AM +0800, JeffleXu wrote:
>>
>>
>> On 7/16/21 8:51 AM, Vivek Goyal wrote:
>>> On Fri, Jul 16, 2021 at 08:40:29AM +0800, Liu Bo wrote:
>>>> On Thu, Jul 15, 2021 at 05:30:31PM +0800, Jeffle Xu wrote:
>>>>> Add one flag for fuse_attr.flags indicating if DAX shall be enabled for
>>>>> this file.
>>>>>
>>>>> When the per-file DAX flag changes for an *opened* file, the state of
>>>>> the file won't be updated until this file is closed and reopened later.
>>>>>
>>>>> Currently it is not implemented yet to change per-file DAX flag inside
>>>>> guest kernel, e.g., by chattr(1).
>>>>
>>>> Thanks for the patch, it looks good to me.
>>>>
>>>> I think it's a good starting point, what I'd like to discuss here is
>>>> whether we're going to let chattr to toggle the dax flag.
>>>
>>> I have the same question. Why not take chattr approach as taken
>>> by ext4/xfs as well.
>>>
>>> Vivek
>>
>> Thanks.
>>
>> We can implement the chattr approach as ext4/xfs do, if we have this use
>> scenario. It's an RFC patch, and I want to collect more feedback as soon
>> as possible.
> 
> I guess chattr approach will allow client (as well as server) to control
> which files should be DAX. While this approach allows only server to
> specify which files should use DAX. Given currently we let client
> control whether to use dax or not (-o dax), it probably will make
> sense to use chattr based approach?

Yes, changing the per-file DAX flag from guest side, such as by chattr,
may be needed for completeness. I will include this in the next version.

> 
> I will look at the patches. Do you have a corresponding user space
> implementation somewhere so that I can test it?

Thanks. I have sent the corresponding patch in-reply-to your mail.

-- 
Thanks,
Jeffle
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