linux-kernel - Re: [PATCH v3 0/2] sched/numa: Skip VMA scanning on memory pinned

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Message-Id: <20250417131236.c47ce477c0e68dbb06a4fabb@linux-foundation.org>
Date: Thu, 17 Apr 2025 13:12:36 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: peterz@...radead.org, mgorman@...e.de, mingo@...hat.com,
 juri.lelli@...hat.com, vincent.guittot@...aro.org, tj@...nel.org,
 rostedt@...dmis.org, llong@...hat.com, kprateek.nayak@....com,
 raghavendra.kt@....com, yu.c.chen@...el.com, tim.c.chen@...el.com,
 vineethr@...ux.ibm.com, chris.hyser@...cle.com, daniel.m.jordan@...cle.com,
 lorenzo.stoakes@...cle.com, mkoutny@...e.com, Dhaval.Giani@....com,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] sched/numa: Skip VMA scanning on memory pinned

On Thu, 17 Apr 2025 12:15:41 -0700 Libo Chen <libo.chen@...cle.com> wrote:

> v1->v2:
> 1. add perf improvment numbers in commit log. Yet to find perf diff on
> will-it-scale, so not included here. Plan to run more workloads.
> 2. add tracepoint.
> 3. To peterz's comment, this will make it impossible to attract tasks to
> those memory just like other VMA skippings. This is the current
> implementation, I think we can improve that in the future, but at the
> moment it's probabaly better to keep it consistent.
> 
> v2->v3:
> 1. add enable_cpuset() based on Mel's suggestion but again I think it's
> redundant
> 2. print out nodemask with %*p.. format in the tracepoint

I do agree with Mel - bitmap_weight() is somewhat expensive and
cpusets_enabled() is super fast.  So the benefit to
cpusets_enabled()=false kernels will exceed to cost to
cpusets_enabled()=true kernels.

This isn't traditionally mm.git material, but it's close.  I'll grab
the patchset for some testing.  and shall drop it again if it turns up
via another tree.