linux-kernel - Re: [PATCH v9 02/10] dax: Introduce holder for dax

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Date:   Thu, 20 Jan 2022 23:17:32 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Shiyang Ruan <ruansy.fnst@...itsu.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        david <david@...morbit.com>, Jane Chu <jane.chu@...cle.com>
Subject: Re: [PATCH v9 02/10] dax: Introduce holder for dax_device

On Thu, Jan 20, 2022 at 06:22:00PM -0800, Darrick J. Wong wrote:
> Hm, so that means XFS can only support dax+pmem when there aren't
> partitions in use?  Ew.

Yes.  Or any sensible DAX usage going forward for that matter.

> 
> > >   (2) extent the holder mechanism to cover a rangeo
> 
> I don't think I was around for the part where "hch balked at a notifier
> call chain" -- what were the objections there, specifically?  I would
> hope that pmem problems would be infrequent enough that the locking
> contention (or rcu expiration) wouldn't be an issue...?

notifiers are a nightmare untype API leading to tons of boilerplate
code.  Open coding the notification is almost always a better idea.