Virtualization - Jul 2021 - [RFC PATCH 3/3] fuse: add per-file DAX flag

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.

-- 
Thanks,
Jeffle

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?

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

Vivek