linux-kernel - Re: [RFC][PATCH 5/8] mm/numa: automatically generate node migration order

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Date:   Wed, 1 Jul 2020 11:23:00 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        yang.shi@...ux.alibaba.com, rientjes@...gle.com,
        dan.j.williams@...el.com
Subject: Re: [RFC][PATCH 5/8] mm/numa: automatically generate node migration
 order

On 6/30/20 1:22 AM, Huang, Ying wrote:
>> +	/*
>> +	 * To avoid cycles in the migration "graph", ensure
>> +	 * that migration sources are not future targets by
>> +	 * setting them in 'used_targets'.
>> +	 *
>> +	 * But, do this only once per pass so that multiple
>> +	 * source nodes can share a target node.
> establish_migrate_target() calls find_next_best_node(), which will set
> target_node in used_targets.  So it seems that the nodes_or() below is
> only necessary to initialize used_targets, and multiple source nodes
> cannot share one target node in current implementation.

Yes, that is true.  My focus on this implementation was simplicity and
sanity for common configurations.  I can certainly imagine scenarios
where this is suboptimal.

I'm totally open to other ways of doing this.