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SubjectRe: [PATCH v2 4/7] mm,memory_hotplug: Enforce struct page size to be multiple of PMD
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On 01.03.21 11:06, Oscar Salvador wrote:
> On Thu, Feb 25, 2021 at 07:26:50PM +0100, David Hildenbrand wrote:
>> On 09.02.21 14:38, Oscar Salvador wrote:
>>> When struct page's size is not multiple of PMD, these do not get
>>> fully populated when adding sections, hence two sections will
>>> intersect the same the PMD. This goes against the vmemmap-per-device
>>> premise, so reject it if that is the case.
>>>
>>> Signed-off-by: Oscar Salvador <osalvador@suse.de>
>>> ---
>>> mm/memory_hotplug.c | 5 +++--
>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 95695483a622..d3fb036d33fd 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -57,10 +57,11 @@ static __meminit int memmap_on_memory_store(const char *val,
>>> const struct kernel_param *kp)
>>> {
>>> /*
>>> - * Fail silently in case we cannot enable it due to platform constraints.
>>> + * Fail silently in case we cannot enable it due to system constraints.
>>> * User can always check whether it is enabled or not via /sys/module.
>>> */
>>> - if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE))
>>> + if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE) ||
>>> + (PMD_SIZE % sizeof(struct page)))
>>> return 0;
>>> return param_set_bool(val, kp);
>>>
>>
>> Squash that into #1 - it's part of basic operation.
>
> Just to be sure we are on the same page.
> You mean to move this patch and patch#5 into the runtime check in
> mhp_supports_memmap_on_memory(), right?

Yes, then the compiler might even be able to figure out that what
follows the check is dead code.

--
Thanks,

David / dhildenb

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