linux-kernel - Re: [PATCH v8 1/9] dax: Use percpu rwsem for dax_{read,write}

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Message-ID: <Ybi69MCK5sP4ebwG@infradead.org>
Date:   Tue, 14 Dec 2021 07:40:36 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, djwong@...nel.org,
        dan.j.williams@...el.com, david@...morbit.com, hch@...radead.org,
        jane.chu@...cle.com
Subject: Re: [PATCH v8 1/9] dax: Use percpu rwsem for dax_{read,write}_lock()

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?

What is the impact of this to benchmarks?  Also if we stop using srcu
protection, we should be able to get rid of grace periods or RCU frees.