linux-kernel - Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove

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Date:   Tue, 4 Jun 2019 08:56:15 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        Dan Williams <dan.j.williams@...el.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove_memory()
 implementation

On 03.06.19 23:41, Wei Yang wrote:
> On Mon, May 27, 2019 at 01:11:45PM +0200, David Hildenbrand wrote:
>> A proper arch_remove_memory() implementation is on its way, which also
>> cleanly removes page tables in arch_add_memory() in case something goes
>> wrong.
> 
> Would this be better to understand?
> 
>     removes page tables created in arch_add_memory

That's not what this sentence expresses. Have a look at
arch_add_memory(), in case  __add_pages() fails, the page tables are not
removed. This will also be fixed by Anshuman in the same shot.

> 
>>
>> As we want to use arch_remove_memory() in case something goes wrong
>> during memory hotplug after arch_add_memory() finished, let's add
>> a temporary hack that is sufficient enough until we get a proper
>> implementation that cleans up page table entries.
>>
>> We will remove CONFIG_MEMORY_HOTREMOVE around this code in follow up
>> patches.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> Cc: Chintan Pandya <cpandya@...eaurora.org>
>> Cc: Mike Rapoport <rppt@...ux.ibm.com>
>> Cc: Jun Yao <yaojun8558363@...il.com>
>> Cc: Yu Zhao <yuzhao@...gle.com>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Cc: Anshuman Khandual <anshuman.khandual@....com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>> arch/arm64/mm/mmu.c | 19 +++++++++++++++++++
>> 1 file changed, 19 insertions(+)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index a1bfc4413982..e569a543c384 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1084,4 +1084,23 @@ int arch_add_memory(int nid, u64 start, u64 size,
>> 	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
>> 			   restrictions);
>> }
>> +#ifdef CONFIG_MEMORY_HOTREMOVE
>> +void arch_remove_memory(int nid, u64 start, u64 size,
>> +			struct vmem_altmap *altmap)
>> +{
>> +	unsigned long start_pfn = start >> PAGE_SHIFT;
>> +	unsigned long nr_pages = size >> PAGE_SHIFT;
>> +	struct zone *zone;
>> +
>> +	/*
>> +	 * FIXME: Cleanup page tables (also in arch_add_memory() in case
>> +	 * adding fails). Until then, this function should only be used
>> +	 * during memory hotplug (adding memory), not for memory
>> +	 * unplug. ARCH_ENABLE_MEMORY_HOTREMOVE must not be
>> +	 * unlocked yet.
>> +	 */
>> +	zone = page_zone(pfn_to_page(start_pfn));
> 
> Compared with arch_remove_memory in x86. If altmap is not NULL, zone will be
> retrieved from page related to altmap. Not sure why this is not the same?

This is a minimal implementation, sufficient for this use case here. A
full implementation is in the works. For now, this function will not be
used with an altmap (ZONE_DEVICE is not esupported for arm64 yet).

Thanks!

> 
>> +	__remove_pages(zone, start_pfn, nr_pages, altmap);
>> +}
>> +#endif
>> #endif
>> -- 
>> 2.20.1
> 


-- 

Thanks,

David / dhildenb