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Date: Fri, 13 Oct 2017 10:14:16 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
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To: Anshuman Khandual <khandual@linux.vnet.ibm.com>
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        Laura Abbott <labbott@redhat.com>, Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP_CONTIG) support
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On Thu, 12 Oct 2017, Anshuman Khandual wrote:

> > +static long __alloc_vma_contig_range(struct vm_area_struct *vma)
> > +{
> > +	gfp_t gfp = GFP_HIGHUSER | __GFP_ZERO;
>
> Would it be GFP_HIGHUSER_MOVABLE instead ? Why __GFP_ZERO ? If its
> coming from Buddy, every thing should have already been zeroed out
> in there. Am I missing something ?

Contiguous pages cannot and should not be moved. They will no longer be
contiguous then. Also the page migration code cannot handle this case.