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Reply-To: Gavin Shan <gshan@redhat.com>
Subject: Re: [PATCH v3] arm64/mm: add fallback option to allocate virtually
 contiguous memory
To:     Anshuman Khandual <anshuman.khandual@arm.com>,
        Sudarshan Rajagopalan <sudaraja@codeaurora.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Mark Rutland <mark.rutland@arm.com>, Will Deacon <will@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Price <steven.price@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Logan Gunthorpe <logang@deltatee.com>
References: <cover.1601582954.git.sudaraja@codeaurora.org>
 <9e6178d2828e9c36275487263c5842c688e5b731.1601582954.git.sudaraja@codeaurora.org>
 <49dd60a7-25f4-8dc1-b905-088dff2a84fb@arm.com>
From:   Gavin Shan <gshan@redhat.com>
Message-ID: <c61139c9-0949-e602-f880-9731eafc7a67@redhat.com>
Date:   Mon, 12 Oct 2020 13:54:40 +1100
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On 10/6/20 2:36 PM, Anshuman Khandual wrote:
> On 10/02/2020 01:46 AM, Sudarshan Rajagopalan wrote:
>> When section mappings are enabled, we allocate vmemmap pages from physically
>> continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). Section
>> mappings are good to reduce TLB pressure. But when system is highly fragmented
>> and memory blocks are being hot-added at runtime, its possible that such
>> physically continuous memory allocations can fail. Rather than failing the
>> memory hot-add procedure, add a fallback option to allocate vmemmap pages from
>> discontinuous pages using vmemmap_populate_basepages().
>>
>> Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/mm/mmu.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>

It looks good to me with Anshuman's comments fixed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 75df62f..11f8639 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1121,8 +1121,15 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>>   			void *p = NULL;
>>   
>>   			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
>> -			if (!p)
>> -				return -ENOMEM;
>> +			if (!p) {
>> +				/*
>> +				 * fallback allocating with virtually
>> +				 * contiguous memory for this section
>> +				 */
> 
> Mapping is always virtually contiguous with or without huge pages.
> Please drop this comment here, as it's obvious.
> 
>> +				if (vmemmap_populate_basepages(addr, next, node, NULL))
>> +					return -ENOMEM;
> 
> Please send in the 'altmap' instead of NULL for allocation from
> device memory if and when requested.
> 
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