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

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v8 1/1] f2fs: dax: implement direct access
Date	2017-07-26 21:20 +0200
Message-ID	<u7A0F-4lW-9@gated-at.bofh.it> (permalink)
References	(2 earlier) <u7oVA-5L0-3@gated-at.bofh.it> <u7xPc-2P1-25@gated-at.bofh.it> <u7xYU-37A-55@gated-at.bofh.it> <u7y8z-3b6-41@gated-at.bofh.it> <u7yig-3eE-63@gated-at.bofh.it>
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On Wed, Jul 26, 2017 at 10:20 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Wed, Jul 26, 2017 at 10:11:08AM -0700, Dan Williams wrote:
>> Until HMAT came along we had no data in the kernel how to pick a sane
>> default, but we could now very easily make a "if pmem performance <
>> dram, disable dax by default" policy in the kernel.
>
> I'd rather do it the other way around - if HMAT is present and
> pmem performance >= dram use dax.  Else require the explicit -o dax
> for now to enable it.  If an explicit -o nodax is specified disable
> DAX even if HMAT says it is faster.

Silently turn on DAX if HMAT says its ok? I think we would instead
want a "-o autodax" for that case and then "-o dax" and "-o nodax" for
the force cases.

>> The question for this patch is do we want to add yet another
>> filesystem that adds "-o dax" or require use of per-inode flags to
>> enable dax.
>
> Please stick to the mount option.  After spending a lot of time with
> DAX and various memory techologies I'm pretty confident that the inode
> flag is the wrong thing to do.

I think it's easier to administer than the dax mount option. If
someone wants dax on only in a sub-tree they can set the flag on that
parent directory and have a policy in dax filesystems that children
inherit the dax policy from the parent. That seems a better
administrative model than trying to get it all right globally at mount
time.

Thread

[PATCH v8 1/1] f2fs: dax: implement direct access sunqiuyang <sunqiuyang@huawei.com> - 2017-07-20 14:10 +0200
  Re: [PATCH v8 1/1] f2fs: dax: implement direct access Jaegeuk Kim <jaegeuk@kernel.org> - 2017-07-22 02:40 +0200
    Re: [PATCH v8 1/1] f2fs: dax: implement direct access Sun Qiuyang <sunqiuyang@huawei.com> - 2017-07-24 14:10 +0200
  Re: [PATCH v8 1/1] f2fs: dax: implement direct access Dan Williams <dan.j.williams@gmail.com> - 2017-07-26 02:20 +0200
    Re: [PATCH v8 1/1] f2fs: dax: implement direct access Jaegeuk Kim <jaegeuk@kernel.org> - 2017-07-26 04:20 +0200
      RE: [PATCH v8 1/1] f2fs: dax: implement direct access sunqiuyang <sunqiuyang@huawei.com> - 2017-07-26 08:50 +0200
    Re: [PATCH v8 1/1] f2fs: dax: implement direct access Christoph Hellwig <hch@infradead.org> - 2017-07-26 09:30 +0200
      Re: [PATCH v8 1/1] f2fs: dax: implement direct access Dan Williams <dan.j.williams@intel.com> - 2017-07-26 19:00 +0200
        Re: [PATCH v8 1/1] f2fs: dax: implement direct access Christoph Hellwig <hch@infradead.org> - 2017-07-26 19:10 +0200
          Re: [PATCH v8 1/1] f2fs: dax: implement direct access Dan Williams <dan.j.williams@intel.com> - 2017-07-26 19:20 +0200
            Re: [PATCH v8 1/1] f2fs: dax: implement direct access Christoph Hellwig <hch@infradead.org> - 2017-07-26 19:30 +0200
              Re: [PATCH v8 1/1] f2fs: dax: implement direct access Dan Williams <dan.j.williams@intel.com> - 2017-07-26 21:20 +0200
                Re: [PATCH v8 1/1] f2fs: dax: implement direct access Christoph Hellwig <hch@infradead.org> - 2017-07-26 22:20 +0200
                Re: [PATCH v8 1/1] f2fs: dax: implement direct access Dan Williams <dan.j.williams@intel.com> - 2017-07-26 22:30 +0200

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