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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <yang.shi@linux.alibaba.com>, <rientjes@google.com>,
        <dan.j.williams@intel.com>
Subject: Re: [RFC][PATCH 5/8] mm/numa: automatically generate node migration order
References: <20200629234503.749E5340@viggo.jf.intel.com>
        <20200629234512.F34EDC44@viggo.jf.intel.com>
        <87ftadotd5.fsf@yhuang-dev.intel.com>
        <3ef8a701-fe8a-cf65-5b72-806b244aae8b@intel.com>
Date:   Thu, 02 Jul 2020 09:20:00 +0800
In-Reply-To: <3ef8a701-fe8a-cf65-5b72-806b244aae8b@intel.com> (Dave Hansen's
        message of "Wed, 1 Jul 2020 11:23:00 -0700")
Message-ID: <878sg2lnlr.fsf@yhuang-dev.intel.com>
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Dave Hansen <dave.hansen@intel.com> writes:

> 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.

OK.  So when we really need to share one target node for multiple source
nodes, we can add a parameter to find_next_best_node() to specify
whether set target_node in used_targets.

Best Regards,
Huang, Ying