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Date:   Sat, 28 Mar 2020 19:59:46 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Alastair D'Silva <alastair@d-silva.org>
Cc:     "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Oliver O'Halloran <oohall@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Frederic Barrat <fbarrat@linux.ibm.com>,
        Andrew Donnellan <ajd@linux.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Anton Blanchard <anton@ozlabs.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
        =?iso-8859-1?Q?C=E9dric?= Le Goater <clg@kaod.org>,
        Anju T Sudhakar <anju@linux.vnet.ibm.com>,
        Hari Bathini <hbathini@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kurz <groug@kaod.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-nvdimm@lists.01.org, linux-mm@kvack.org
Subject: Re: [PATCH v4 10/25] nvdimm: Add driver for OpenCAPI Persistent
 Memory
Message-ID: <20200329025946.GU22483@bombadil.infradead.org>
References: <20200327071202.2159885-1-alastair@d-silva.org>
 <20200327071202.2159885-11-alastair@d-silva.org>
 <20200329025617.GT22483@bombadil.infradead.org>
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On Sat, Mar 28, 2020 at 07:56:17PM -0700, Matthew Wilcox wrote:
> On Fri, Mar 27, 2020 at 06:11:47PM +1100, Alastair D'Silva wrote:
> > +static struct mutex minors_idr_lock;
> > +static struct idr minors_idr;
> ...
> > +	mutex_lock(&minors_idr_lock);
> > +	minor = idr_alloc(&minors_idr, ocxlpmem, 0, NUM_MINORS, GFP_KERNEL);
> > +	mutex_unlock(&minors_idr_lock);
> ...
> > +	mutex_lock(&minors_idr_lock);
> > +	idr_remove(&minors_idr, MINOR(ocxlpmem->dev.devt));
> > +	mutex_unlock(&minors_idr_lock);
> ...
> > +	mutex_init(&minors_idr_lock);
> > +	idr_init(&minors_idr);
> 
> Unless you look up ocxlpmem by minor number later in the patch series (and
> most of the series didn't make it to my mailbox), this can just be an ida.
> 
> static DEFINE_IDA(minors);
> ...
> minor = ida_alloc_max(&minors, NUM_MINORS, GFP_KERNEL);

Oops.  NUM_MINORS - 1.  Or #define MAX_MINOR 255 since you only seem to use
NUM_MINORS in this one place.

> ...
> ida_free(&minors, MINOR(ocxlpmem->dev.devt));
> ...
> and you can drop the dynamic initialisation.  And the mutex.