linux-kernel - Re: [PATCH -V6 RESEND 1/3] numa balancing: Migrate on fault among multiple bound nodes

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Date:   Thu, 3 Dec 2020 10:53:13 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Huang Ying <ying.huang@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>, linux-api@...r.kernel.org
Subject: Re: [PATCH -V6 RESEND 1/3] numa balancing: Migrate on fault among
 multiple bound nodes

On Thu, Dec 03, 2020 at 11:25:50AM +0100, Peter Zijlstra wrote:
> On Wed, Dec 02, 2020 at 11:40:54AM +0000, Mel Gorman wrote:
> > On Wed, Dec 02, 2020 at 04:42:32PM +0800, Huang Ying wrote:
> > > Now, NUMA balancing can only optimize the page placement among the
> > > NUMA nodes if the default memory policy is used.  Because the memory
> > > policy specified explicitly should take precedence.  But this seems
> > > too strict in some situations.  For example, on a system with 4 NUMA
> > > nodes, if the memory of an application is bound to the node 0 and 1,
> > > NUMA balancing can potentially migrate the pages between the node 0
> > > and 1 to reduce cross-node accessing without breaking the explicit
> > > memory binding policy.
> > > 
> > 
> > Ok, I think this part is ok and while the test case is somewhat
> > superficial, it at least demonstrated that the NUMA balancing overhead
> > did not offset any potential benefit
> > 
> > Acked-by: Mel Gorman <mgorman@...e.de>
> 
> Who do we expect to merge this, me through tip/sched/core or akpm ?

I would expect akpm, it's much more on the mm side because it affects
the semantics of memory policies. It should also have more mm-orientated
review than just mine because it affects user-visible semantics and the
ability to detect whether the feature is available or not needs to be
treated with care.

-- 
Mel Gorman
SUSE Labs