From: Andrew Morton <akpm@linux-foundation.org>
To: Oscar Salvador <osalvador@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
"Huang, Ying" <ying.huang@intel.com>,
Abhishek Goel <huntbag@linux.vnet.ibm.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm: Only re-generate demotion targets when a numa node changes its N_CPU state
Date: Thu, 10 Mar 2022 18:39:51 -0800 [thread overview]
Message-ID: <20220310183951.cb713c6ae926ea6ea8489a71@linux-foundation.org> (raw)
In-Reply-To: <20220310120749.23077-1-osalvador@suse.de>
On Thu, 10 Mar 2022 13:07:49 +0100 Oscar Salvador <osalvador@suse.de> wrote:
> Abhishek reported that after patch [1], hotplug operations are
> taking ~double the expected time. [2]
>
> The reason behind is that the CPU callbacks that migrate_on_reclaim_init()
> sets always call set_migration_target_nodes() whenever a CPU is brought
> up/down.
> But we only care about numa nodes going from having cpus to become
> cpuless, and vice versa, as that influences the demotion_target order.
>
> We do already have two CPU callbacks (vmstat_cpu_online() and vmstat_cpu_dead())
> that check exactly that, so get rid of the CPU callbacks in
> migrate_on_reclaim_init() and only call set_migration_target_nodes() from
> vmstat_cpu_{dead,online}() whenever a numa node change its N_CPU state.
What I'm not getting here (as so often happens) is a sense of how badly
this affects our users. Does anyone actually hotplug frequently enough
to care?
If "yes" then I'm inclined to merge this up for 5.18 with a cc:stable.
Not for 5.17 because it's late and things are looking rather creaky
already.
And I'll add a
Fixes: 884a6e5d1f93b ("mm/migrate: update node demotion order on hotplug events")
which is that patch's fourth such bouquet.
next prev parent reply other threads:[~2022-03-11 2:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-10 12:07 [PATCH v2] mm: Only re-generate demotion targets when a numa node changes its N_CPU state Oscar Salvador
2022-03-11 1:33 ` Baolin Wang
2022-03-11 2:24 ` Huang, Ying
2022-03-11 8:39 ` Oscar Salvador
2022-03-14 1:03 ` Huang, Ying
2022-03-14 15:13 ` Oscar Salvador
2022-03-14 15:20 ` Dave Hansen
2022-03-15 6:13 ` Oscar Salvador
2022-03-15 6:31 ` Huang, Ying
2022-03-11 2:39 ` Andrew Morton [this message]
2022-03-11 9:23 ` Oscar Salvador
2022-03-11 17:10 ` Dave Hansen
2022-03-14 9:09 ` Abhishek Goel
2022-03-11 5:06 ` Huang, Ying
2022-03-11 9:17 ` Oscar Salvador
2022-03-14 3:09 ` Huang, Ying
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