linux-kernel - Re: [PATCH 0/5] [v5] Allow persistent memory to be used like normal RAM

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Date:   Wed, 27 Feb 2019 23:53:52 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        "Huang, Ying" <ying.huang@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Takashi Iwai <tiwai@...e.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Keith Busch <keith.busch@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH 0/5] [v5] Allow persistent memory to be used like normal RAM

[ add Stephen and Juergen ]

On Mon, Feb 25, 2019 at 11:02 AM Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> This is a relatively small delta from v4.  The review comments seem
> to be settling down, so it seems like we should start thinking about
> how this might get merged.  Are there any objections to taking it in
> via the nvdimm tree?
>
> Dan Williams, our intrepid nvdimm maintainer has said he would
> appreciate acks on these from relevant folks before merging them.
> Reviews/acks on any in the series would be welcome, but the last
> two especially are lacking any non-Intel acks:
>
>         mm/resource: let walk_system_ram_range() search child resources
>         dax: "Hotplug" persistent memory for use like normal RAM

I've gone ahead and added this to the libnvdimm-for-next branch for
wider exposure. Acks of course still welcome.

Stephen, this collides with commit 357b4da50a62 "x86: respect memory
size limiting via mem= parameter" in current -next. Here's my
resolution for reference, basically just add the max_mem_size
statement to Dave's rework. Holler if this causes any other problems.

diff --cc mm/memory_hotplug.c
index a9d5787044e1,b37f3a5c4833..c4f59ac21014
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@@ -102,28 -99,21 +102,24 @@@ u64 max_mem_size = U64_MAX
  /* add this memory to iomem resource */
  static struct resource *register_memory_resource(u64 start, u64 size)
  {
-       struct resource *res, *conflict;
+       struct resource *res;
+       unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+       char *resource_name = "System RAM";

 +      if (start + size > max_mem_size)
 +              return ERR_PTR(-E2BIG);
 +
-       res = kzalloc(sizeof(struct resource), GFP_KERNEL);
-       if (!res)
-               return ERR_PTR(-ENOMEM);
-
-       res->name = "System RAM";
-       res->start = start;
-       res->end = start + size - 1;
-       res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
-       conflict =  request_resource_conflict(&iomem_resource, res);
-       if (conflict) {
-               if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
-                       pr_debug("Device unaddressable memory block "
-                                "memory hotplug at %#010llx !\n",
-                                (unsigned long long)start);
-               }
-               pr_debug("System RAM resource %pR cannot be added\n", res);
-               kfree(res);
+       /*
+        * Request ownership of the new memory range.  This might be
+        * a child of an existing resource that was present but
+        * not marked as busy.
+        */
+       res = __request_region(&iomem_resource, start, size,
+                              resource_name, flags);
+
+       if (!res) {
+               pr_debug("Unable to reserve System RAM region:
%016llx->%016llx\n",
+                               start, start + size);
                return ERR_PTR(-EEXIST);
        }
        return res;