Date:   Wed, 15 Dec 2021 23:46:05 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
        nvdimm@lists.linux.dev, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, djwong@kernel.org,
        dan.j.williams@intel.com, david@fromorbit.com, jane.chu@oracle.com
Subject: Re: [PATCH v8 1/9] dax: Use percpu rwsem for dax_{read,write}_lock()
Message-ID: <YbruvTOVwwRhRLU8@infradead.org>
References: <20211202084856.1285285-1-ruansy.fnst@fujitsu.com>
 <20211202084856.1285285-2-ruansy.fnst@fujitsu.com>
 <Ybi69MCK5sP4ebwG@infradead.org>
 <bc5743cb-f79e-2f67-d594-85b56f05bda3@fujitsu.com>
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On Wed, Dec 15, 2021 at 10:06:29AM +0800, Shiyang Ruan wrote:
> 
> 
> 在 2021/12/14 23:40, Christoph Hellwig 写道:
> > On Thu, Dec 02, 2021 at 04:48:48PM +0800, Shiyang Ruan wrote:
> > > In order to introduce dax holder registration, we need a write lock for
> > > dax.  Change the current lock to percpu_rw_semaphore and introduce a
> > > write lock for registration.
> > 
> > Why do we need to change the existing, global locking for that?
> 
> I think we have talked about this in the previous v7 patchset:
> 
> 
> https://lore.kernel.org/nvdimm/20210924130959.2695749-1-ruansy.fnst@fujitsu.com/T/#m4031bc3dc49dcbaac6f8d99877f910fa9a6f998a

Any kind of rationale needs to go into the patch description.

> I didn't test in benchmarks for now.  Could you show me which one I should
> test this code on?  I am not familiar with this...

Just normal read/write I/O on a DAX device.