linux-kernel - Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave

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Message-ID: <oe7s47mjbemtfsc3tbhweeiledh4srjntrsyohsvpy5m4jsgsb@xjl7u5a3p3z3>
Date:   Fri, 3 Nov 2023 17:59:00 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        linux-mm@...ck.org, ying.huang@...el.com,
        akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
        weixugc@...gle.com, apopple@...dia.com, tim.c.chen@...el.com,
        dave.hansen@...el.com, shy828301@...il.com,
        gregkh@...uxfoundation.org, rafael@...nel.org
Subject: Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave

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