linux-kernel - Re: [PATCH v6 2/6] mm/memplicy: add page allocation function for MPOL_PREFERRED

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Date:   Wed, 28 Jul 2021 18:14:41 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, ying.huang@...el.com
Subject: Re: [PATCH v6 2/6] mm/memplicy: add page allocation function for
 MPOL_PREFERRED_MANY policy

On Wed 28-07-21 23:18:10, Feng Tang wrote:
> On Wed, Jul 28, 2021 at 02:42:26PM +0200, Michal Hocko wrote:
> > On Mon 12-07-21 16:09:30, Feng Tang wrote:
> > > The semantics of MPOL_PREFERRED_MANY is similar to MPOL_PREFERRED,
> > > that it will first try to allocate memory from the preferred node(s),
> > > and fallback to all nodes in system when first try fails.
> > > 
> > > Add a dedicated function for it just like 'interleave' policy.
> > > 
> > > Link: https://lore.kernel.org/r/20200630212517.308045-9-ben.widawsky@intel.com
> > > Suggested-by: Michal Hocko <mhocko@...e.com>
> > > Co-developed-by: Ben Widawsky <ben.widawsky@...el.com>
> > > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> > > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > 
> > It would be better to squash this together with the actual user of the
> > function added by the next patch.
>  
> Ok, will do
> 
> > > ---
> > >  mm/mempolicy.c | 19 +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > > index 17b5800b7dcc..d17bf018efcc 100644
> > > --- a/mm/mempolicy.c
> > > +++ b/mm/mempolicy.c
> > > @@ -2153,6 +2153,25 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
> > >  	return page;
> > >  }
> > >  
> > > +static struct page *alloc_page_preferred_many(gfp_t gfp, unsigned int order,
> > > +						struct mempolicy *pol)
> > 
> > We likely want a node parameter to know which one we want to start with
> > for locality. Callers should use policy_node for that.
>  
> Yes, locality should be considered, something like this?
> 
> 	int pnid, lnid = numa_node_id();
> 
> 	if (is_nodeset(lnid, &pol->nodes))
> 		pnid = local_nid;
> 	else
> 		pnid = first_node(pol->nodes);
> 
> 	page = __alloc_pages(((gfp | __GFP_NOWARN) & ~__GFP_DIRECT_RECLAIM),
> 				order, pnid, &pol->nodes);
> 	if (!page)
> 		page = __alloc_pages(gfp, order, lnid, NULL);
> 	return page;

No. I really meant to get a node argument and use it as it is. Your
callers already have some node preferences. Usually a local node and as
we have a nodemask here then we do not really need to have any special
logic here as mentioned in other email. The preferred node will act only
as a source for the zone list.
-- 
Michal Hocko
SUSE Labs