From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset
 and bail out early
Date: Tue, 14 Sep 2021 10:17:52 +0200
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To: Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>
Cc: Feng Tang <feng.tang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Mel Gorman <mgorman-3eNAlZScCAx27rWaFMvyedHuzzzSOjJt@public.gmane.org>, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Tue 14-09-21 10:01:26, Vlastimil Babka wrote:
> On 9/14/21 05:40, Feng Tang wrote:
[...]
> > +/* Whether the 'nodes' are all movable nodes */
> > +static inline bool movable_only_nodes(nodemask_t *nodes)
> > +{
> > +	struct zonelist *zonelist;
> > +	struct zoneref *z;
> > +
> > +	if (nodes_empty(*nodes))
> > +		return false;
> > +
> > +	zonelist =
> > +	    &NODE_DATA(first_node(*nodes))->node_zonelists[ZONELIST_FALLBACK];
> > +	z = first_zones_zonelist(zonelist, ZONE_NORMAL,	nodes);
> > +	return (!z->zone) ? true : false;
> > +}
> 
> Hmm, could all that become just this?
> 
> !nodes_intersects(&node_states[N_NORMAL_MEMORY], nodes)

Maybe yes but I find the zonelist approach much easier to follow even
though the code looks more complex at first sight. It talks about an
empty zone list for ZONE_NORMAL request which is quite clear from the
scribble. I always have to re-learn how the N*MEMORY works TBH. Maybe
this is just me though.
-- 
Michal Hocko
SUSE Labs