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Date:   Fri, 3 Nov 2023 17:59:00 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Gregory Price <gregory.price@memverge.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Gregory Price <gourry.memverge@gmail.com>,
        linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org,
        linux-mm@kvack.org, ying.huang@intel.com,
        akpm@linux-foundation.org, aneesh.kumar@linux.ibm.com,
        weixugc@google.com, apopple@nvidia.com, tim.c.chen@intel.com,
        dave.hansen@intel.com, shy828301@gmail.com,
        gregkh@linuxfoundation.org, rafael@kernel.org
Subject: Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave
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On Thu 02-11-23 14:21:14, Gregory Price wrote:
[...]
> Only thing I'm not sure of is what happens if mempolicy is allowed to
> select a node that doesn't exist.  I could hack up a contrived test, but
> i don't think the state is reachable at the moment.

There are two different kinds of doesn't exist. One is an offline node
and the other is one with a number higher than the config option allows.
Although we do have a concept of possible nodes N_POSSIBLE I do not
think we do enforce that in any user interface and we only reject nodes
outside of MAX_NODE.

The possible nodes concept is more about optimizing for real HW so that
we do not over shoot when the config allows a huge number of nodes while
only handful of them are actually used (which is the majority of cases).
-- 
Michal Hocko
SUSE Labs