linux-kernel - Re: [PATCH 4/4] dax: "Hotplug" persistent memory for use like normal RAM

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Message-ID: <CAErSpo6xjELcvj1jZ20UZS-rEHr-kNioPFTjWR9K3CuZq8ecmw@mail.gmail.com>
Date:   Wed, 16 Jan 2019 15:59:28 -0600
From:   Bjorn Helgaas <bhelgaas@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Dave Hansen <dave@...1.net>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, zwisler@...nel.org,
        vishal.l.verma@...el.com, thomas.lendacky@....com,
        Andrew Morton <akpm@...ux-foundation.org>, mhocko@...e.com,
        linux-nvdimm@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Huang Ying <ying.huang@...el.com>,
        Wu Fengguang <fengguang.wu@...el.com>,
        Borislav Petkov <bp@...e.de>, baiyaowei@...s.chinamobile.com,
        Takashi Iwai <tiwai@...e.de>
Subject: Re: [PATCH 4/4] dax: "Hotplug" persistent memory for use like normal RAM

On Wed, Jan 16, 2019 at 3:53 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 1/16/19 1:16 PM, Bjorn Helgaas wrote:
> >> +       /*
> >> +        * Set flags appropriate for System RAM.  Leave ..._BUSY clear
> >> +        * so that add_memory() can add a child resource.
> >> +        */
> >> +       new_res->flags = IORESOURCE_SYSTEM_RAM;
> > IIUC, new_res->flags was set to "IORESOURCE_MEM | ..." in the
> > devm_request_mem_region() path.  I think you should keep at least
> > IORESOURCE_MEM so the iomem_resource tree stays consistent.
>
> I went to look at fixing this.  It looks like "IORESOURCE_SYSTEM_RAM"
> includes IORESOURCE_MEM:
>
> > #define IORESOURCE_SYSTEM_RAM           (IORESOURCE_MEM|IORESOURCE_SYSRAM)
>
> Did you want the patch to expand this #define, or did you just want to
> ensure that IORESORUCE_MEM got in there somehow?

The latter.  Since it's already included, forget I said anything :)
Although if your intent is only to clear IORESOURCE_BUSY, maybe it
would be safer to just clear that bit instead of overwriting
everything?  That might also help people grepping for IORESOURCE_BUSY
usage.