Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask

[David Rientjes <rientjes@google.com>]

On Wed, 26 Sep 2018, Kirill A. Shutemov wrote:

> On Tue, Sep 25, 2018 at 02:03:26PM +0200, Michal Hocko wrote:
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index c3bc7e9c9a2a..c0bcede31930 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -629,21 +629,40 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> >   *	    available
> >   * never: never stall for any thp allocation
> >   */
> > -static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
> > +static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma, unsigned long addr)
> >  {
> >  	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
> > +	gfp_t this_node = 0;
> > +
> > +#ifdef CONFIG_NUMA
> > +	struct mempolicy *pol;
> > +	/*
> > +	 * __GFP_THISNODE is used only when __GFP_DIRECT_RECLAIM is not
> > +	 * specified, to express a general desire to stay on the current
> > +	 * node for optimistic allocation attempts. If the defrag mode
> > +	 * and/or madvise hint requires the direct reclaim then we prefer
> > +	 * to fallback to other node rather than node reclaim because that
> > +	 * can lead to excessive reclaim even though there is free memory
> > +	 * on other nodes. We expect that NUMA preferences are specified
> > +	 * by memory policies.
> > +	 */
> > +	pol = get_vma_policy(vma, addr);
> > +	if (pol->mode != MPOL_BIND)
> > +		this_node = __GFP_THISNODE;
> > +	mpol_cond_put(pol);
> > +#endif
> 
> I'm not very good with NUMA policies. Could you explain in more details how
> the code above is equivalent to the code below?
> 

It breaks mbind() because new_page() is now using numa_node_id() to 
allocate migration targets for instead of using the mempolicy.  I'm not 
sure that this patch was tested for mbind().