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Subject: Re: [Patch v2] mm/hotplug: Only respect mem= parameter during boot
 stage
To:     Baoquan He <bhe@redhat.com>, linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, mhocko@kernel.org, jgross@suse.com,
        akpm@linux-foundation.org
References: <20191210084413.21957-1-bhe@redhat.com>
From:   David Hildenbrand <david@redhat.com>
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Message-ID: <1a7a6ae6-e229-981c-9113-0a96683320a0@redhat.com>
Date:   Tue, 10 Dec 2019 10:32:34 +0100
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On 10.12.19 09:44, Baoquan He wrote:
> In commit 357b4da50a62 ("x86: respect memory size limiting via mem=3D
> parameter") a global varialbe global max_mem_size is added to store

Only some nits:

s/varialbe global/variable/

> the value parsed from 'mem=3D ', then checked when memory region is
> added. This truly stops those DIMM from being added into system memory
s/DIMM/DIMMs/

> during boot-time.
>=20
> However, it also limits the later memory hotplug functionality. Any
> memory board can't be hot added any more if its region is beyond the

s/memory board/DIMM/ ?

s/hot added/hotplugged/ ?

> max_mem_size. System will print error like below:

"We will get errors like:"

>=20
> [  216.387164] acpi PNP0C80:02: add_memory failed
> [  216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
> [  216.392187] acpi PNP0C80:02: Enumeration failure
>=20
> From document of 'mem=3D ' parameter, it should be a restriction during

"the documentation of the"

> boot, but not impact the system memory adding/removing after booting.

"but not impact memory hotplug once booted."

>=20
>   mem=3Dnn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
> =09          ...
>=20
> So fix it by also checking if it's during boot-time when restrict memory

s/when restrict memory adding/restricting to add memory/

> adding. Otherwise, skip the restriction.
>=20
> Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem=3D parame=
ter")
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/memory_hotplug.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>=20
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 55ac23ef11c1..989707295d15 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -105,7 +105,11 @@ static struct resource *register_memory_resource(u64=
 start, u64 size)
>  =09unsigned long flags =3D  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>  =09char *resource_name =3D "System RAM";
> =20
> -=09if (start + size > max_mem_size)
> +=09/*
> +=09 * Make sure value parsed from 'mem=3D' only restricts memory adding
> +=09 * during boot-time, so that memory hotplug won't be impacted.

s/during boot-time/while booting/

Only some nits, thanks!

Reviewed-by: David Hildenbrand <david@redhat.com>

--=20
Thanks,

David / dhildenb