linux-kernel - Re: [PATCH v2 3/3] device-dax: Add system ram (add_memory()) with MHP_NO_FIRMWARE

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Date:   Thu, 30 Apr 2020 04:23:42 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, virtio-dev@...ts.oasis-open.org,
        virtualization@...ts.linux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-hyperv@...r.kernel.org,
        linux-s390@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Baoquan He <bhe@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 3/3] device-dax: Add system ram (add_memory()) with
 MHP_NO_FIRMWARE_MEMMAP

On 4/30/20 3:29 AM, David Hildenbrand wrote:
> Currently, when adding memory, we create entries in /sys/firmware/memmap/
> as "System RAM". This does not reflect the reality and will lead to
> kexec-tools to add that memory to the fixed-up initial memmap for a
> kexec kernel (loaded via kexec_load()). The memory will be considered
> initial System RAM by the kexec kernel.
> 
> We should let the kexec kernel decide how to use that memory - just as
> we do during an ordinary reboot.
...
> -	rc = add_memory(numa_node, new_res->start, resource_size(new_res), 0);
> +	rc = add_memory(numa_node, new_res->start, resource_size(new_res),
> +			MHP_NO_FIRMWARE_MEMMAP);

Looks fine.  But, if you send another revision, could you add a comment
about the actual goal of MHP_NO_FIRMWARE_MEMMAP?  Maybe:

	/*
	 * MHP_NO_FIRMWARE_MEMMAP ensures that future
	 * kexec'd kernels will not treat this as RAM.
	 */

Not a biggie, though.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>