linux-ext4 - Re: [LSF/MM TOPIC] The end of the DAX experiment

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Date:   Fri, 8 Feb 2019 10:02:45 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     "Kani, Toshi" <toshi.kani@....com>
Cc:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "lsf-pc@...ts.linux-foundation.org" 
        <lsf-pc@...ts.linux-foundation.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [LSF/MM TOPIC] The end of the DAX experiment

On 07/02/2019 22:51, Kani, Toshi wrote:
> I've also had multiple users complained about 'mount -o dax' succeeded
> by falling back to non-dax despite of their intent.  Such users wasted
> many hours without knowing their setup error / current restrictions.
> The next think they always ask is how to check if dax is enabled in such
> case, and they are not happy about limited interfaces (ex. look for
> mount entry in /proc/mounts), either.

Exactly, there's a need for admins and user-space applications to check if they
can use DAX or not. See also [1] for reference.

> Same as above.  Such enhancement should be possible after EXPERIMENTAL
> is removed from 'mount -o dax'.  IOW, a separate EXPERIMENTAL message
> can be shown when user requests per-directory dax.

Just as a data point here, in our Kernels we've removed the EXPERIMENTAL
warning for DAX on XFS (but not EXT4) and we are supporting it for some limited
use-cases.

[1] https://lore.kernel.org/linux-fsdevel/20181002100531.GC4135@quack2.suse.cz/

Byte,
        Johannes
-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@...e.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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