Re: [PATCH v3] arm64/mm: add fallback option to allocate virtually contiguous memory

[Sudarshan Rajagopalan]

On 2020-10-13 04:38, Anshuman Khandual wrote:
> On 10/13/2020 04:35 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().
>
> There is a checkpatch warning here, which could be fixed while merging 
> ?
>
> WARNING: Possible unwrapped commit description (prefer a maximum 75
> chars per line)
> #7:
> When section mappings are enabled, we allocate vmemmap pages from 
> physically
>
> total: 0 errors, 1 warnings, 13 lines checked

Thanks Anshuman for the review. I sent out an updated patch fixing the 
checkpatch warning.

> > Signed-off-by: Sudarshan Rajagopalan <sudaraja@xxxxxxxxxxxxxx>
> > Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Steven Price <steven.price@xxxxxxx>
>
> Nonetheless, this looks fine. Did not see any particular problem
> while creating an experimental vmemmap with interleaving section
> and base page mapping.
>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>
> > ---
> >  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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