[PATCH v4] arm64/mm: add fallback option to allocate virtually contiguous memory

[Sudarshan Rajagopalan]

On 2020-10-16 11:56, Sudarshan Rajagopalan wrote:

Hello Will, Catalin,

Did you have a chance to review this patch? It is reviewed by others and 
haven't seen any Nacks. This patch will be useful to have so that memory 
hotremove doesn't fail when such PMD_SIZE pages aren't available.. which 
is usually the case in low RAM devices.

> 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 at codeaurora.org>
> Reviewed-by: Gavin Shan <gshan at redhat.com>
> Reviewed-by: Anshuman Khandual <anshuman.khandual at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Logan Gunthorpe <logang at deltatee.com>
> Cc: David Hildenbrand <david at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Steven Price <steven.price at arm.com>
> ---
>  arch/arm64/mm/mmu.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62fea1b6..44486fd0e883 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1121,8 +1121,11 @@ 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) {
> +				if (vmemmap_populate_basepages(addr, next, node, altmap))
> +					return -ENOMEM;
> +				continue;
> +			}
> 
>  			pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
>  		} else

-- 
Sudarshan

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