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SubjectRe: [PATCH 3/5] mm/memory_hotplug: Check for IORESOURCE_SYSRAM in release_mem_region_adjustable
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On 15/10/2018 17:30, Oscar Salvador wrote:
> From: Oscar Salvador <osalvador@suse.de>
>
> This is a preparation for the next patch.
>
> Currently, we only call release_mem_region_adjustable() in __remove_pages
> if the zone is not ZONE_DEVICE, because resources that belong to
> HMM/devm are being released by themselves with devm_release_mem_region.
>
> Since we do not want to touch any zone/page stuff during the removing
> of the memory (but during the offlining), we do not want to check for
> the zone here.
> So we need another way to tell release_mem_region_adjustable() to not
> realease the resource in case it belongs to HMM/devm.
>
> HMM/devm acquires/releases a resource through
> devm_request_mem_region/devm_release_mem_region.
>
> These resources have the flag IORESOURCE_MEM, while resources acquired by
> hot-add memory path (register_memory_resource()) contain
> IORESOURCE_SYSTEM_RAM.
>
> So, we can check for this flag in release_mem_region_adjustable, and if
> the resource does not contain such flag, we know that we are dealing with
> a HMM/devm resource, so we can back off.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
> kernel/resource.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 81937830a42f..c45decd7d6af 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -1272,6 +1272,22 @@ int release_mem_region_adjustable(struct resource *parent,
> continue;
> }
>
> + /*
> + * All memory regions added from memory-hotplug path
> + * have the flag IORESOURCE_SYSTEM_RAM.
> + * If the resource does not have this flag, we know that
> + * we are dealing with a resource coming from HMM/devm.
> + * HMM/devm use another mechanism to add/release a resource.
> + * This goes via devm_request_mem_region and
> + * devm_release_mem_region.
> + * HMM/devm take care to release their resources when they want,
> + * so if we are dealing with them, let us just back off here.
> + */
> + if (!(res->flags & IORESOURCE_SYSRAM)) {
> + ret = 0;
> + break;
> + }
> +
> if (!(res->flags & IORESOURCE_MEM))
> break;
>
>

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

--

Thanks,

David / dhildenb

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