linux-kernel - Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct

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Date:   Tue, 9 Oct 2018 14:36:35 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Argangeli <andrea@...nel.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into
 alloc_hugepage_direct_gfpmask

On Thu 04-10-18 13:17:52, David Rientjes wrote:
> 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().

I am sorry but I do not follow, could you be more specific please?
MPOL_BIND should never get __GFP_THISNODE. What am I missing?

-- 
Michal Hocko
SUSE Labs