linux-kernel - Re: [PATCH v8 1/1] f2fs: dax: implement direct access

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Date:   Tue, 25 Jul 2017 19:16:20 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Dan Williams <dan.j.williams@...il.com>
Cc:     sunqiuyang <sunqiuyang@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>
Subject: Re: [PATCH v8 1/1] f2fs: dax: implement direct access

Hi Dan,

On 07/25, Dan Williams wrote:
> [ adding linux-nvdimm ]
> 
> On Thu, Jul 20, 2017 at 5:10 AM, sunqiuyang <sunqiuyang@...wei.com> wrote:
> > From: Qiuyang Sun <sunqiuyang@...wei.com>
> >
> > This patch implements Direct Access (DAX) in F2FS, including:
> >  - a mount option to choose whether to enable DAX or not
> 
> We're in the process of walking back and potentially deprecating the
> use of the dax mount option for xfs and ext4 since dax can have
> negative performance implications if page cache memory happens to be
> faster than pmem. It should be limited to applications that
> specifically want the semantic, not globally enabled for the entire
> mount. xfs has went ahead and added the XFS_DIFLAG2_DAX indoe flag for
> per-inode enabling of dax.

Thank you so much for pointing this out. So, is there a plan to define a
generic inode flag to enable dax via inode_set_flag? Or, does each filesystem
need to handle it individually likewise xfs?

> 
> I'm wondering if any new filesystem that adds dax support at this
> point should do so with inode flags and not a mount option?

Anyway, in such the case, I have to postpone merging this patch for a while.

Thanks,