linux-kernel - Re: [PATCH v2] mm/page_alloc: detect allocation forbidden by cpuset and bail out early

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Message-ID: <YT8576cL4tSqmUKI@dhcp22.suse.cz>
Date:   Mon, 13 Sep 2021 13:45:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     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>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page_alloc: detect allocation forbidden by cpuset
 and bail out early

On Mon 13-09-21 19:34:23, Feng Tang wrote:
> On Mon, Sep 13, 2021 at 11:15:54AM +0200, Michal Hocko wrote:
[...] 
> > > +/* Whether the 'nodes' are all movable nodes */
> > > +static inline bool movable_only_nodes(nodemask_t *nodes)
> > > +{
> > > +	struct zonelist *zonelist;
> > > +	struct zoneref *z;
> > > +
> > > +	zonelist = &(first_online_pgdat())->node_zonelists[ZONELIST_FALLBACK];
> > 
> > This will work but it just begs a question why you haven't chosen a node
> > from the given nodemask. So I believe it would be easier to read if you
> > did
> > 	zonelist = NODE_DATA(first_node(nodes))->node_zonelists[ZONELIST_FALLBACK]
> 
> This was also my first try to get the 'zonelist', but from the
> update_nodemask(), the nodemask could be NULL.

I guess you meant to say s@...L@...ty@
While this complicates things a bit it is nothing really hard to work
around. You simply check for nodes_empty() and return false because such
a nodemask cannot by definition be movable only.
-- 
Michal Hocko
SUSE Labs