linux-kernel - Re: [PATCH v3 03/10] efi: Enumerate EFI_MEMORY

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Date:   Fri, 7 Jun 2019 15:07:19 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        X86 ML <x86@...nel.org>, linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v3 03/10] efi: Enumerate EFI_MEMORY_SP

On Fri, Jun 7, 2019 at 2:12 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 6/7/19 1:03 PM, Dan Williams wrote:
> >> Separate from these patches, should we have a runtime file that dumps
> >> out the same info?  dmesg isn't always available, and hotplug could
> >> change this too, I'd imagine.
> > Perhaps, but I thought /proc/iomem was that runtime file. Given that
> > x86/Linux only seems to care about the the EFI to E820 translation of
> > the map and the E820 map is directly reflected in /proc/iomem, do we
> > need another file?
>
> Probably not.
>
> I'm just trying to think of ways that we can debug systems where someone
> "loses" a bunch of memory, especially if they're moving from an old
> kernel to a new one with these patches.  From their perspective, they
> just lost a bunch of expensive memory.
>
> Do we owe a pr_info(), perhaps?  Or even a /proc/meminfo entry for how
> much memory these devices own?

We have this existing print when this bit is found:

[    0.023650] e820: update [mem 0x240000000-0x43fffffff] usable ==>
application reserved

...but perhaps /proc/meminfo could grow:

ApplicationReservedOffline
ApplicationReservedOnline

...to show the relative amount of this memory that has been routed to
device-dax and how much has been returned to the core-mm?