linux-kernel - Re: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset and bail out early

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Message-ID: <YUBasMWLAjzcgtt9@dhcp22.suse.cz>
Date:   Tue, 14 Sep 2021 10:17:52 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Feng Tang <feng.tang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset
 and bail out early

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