linux-kernel - Re: [PATCH -V10 2/9] mm/migrate: update node demotion order on hotplug events

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Message-ID: <FDEEF381-7672-458B-949D-9F5D8D9003B5@nvidia.com>
Date:   Thu, 15 Jul 2021 14:00:49 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        Wei Xu <weixugc@...gle.com>, osalvador <osalvador@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH -V10 2/9] mm/migrate: update node demotion order on hotplug events

On 15 Jul 2021, at 1:51, Huang Ying wrote:

> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Reclaim-based migration is attempting to optimize data placement in
> memory based on the system topology.  If the system changes, so must
> the migration ordering.
>
> The implementation is conceptually simple and entirely unoptimized.
> On any memory or CPU hotplug events, assume that a node was added or
> removed and recalculate all migration targets.  This ensures that the
> node_demotion[] array is always ready to be used in case the new
> reclaim mode is enabled.
>
> This recalculation is far from optimal, most glaringly that it does
> not even attempt to figure out the hotplug event would have some
> *actual* effect on the demotion order.  But, given the expected
> paucity of hotplug events, this should be fine.
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Reviewed-by: Yang Shi <shy828301@...il.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Wei Xu <weixugc@...gle.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: osalvador <osalvador@...e.de>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
>
> --
>
> Changes since 20210618:
>  * moved RCU part to the prev patch in series.
>
> Changes since 20210302:
>  * remove duplicate synchronize_rcu()
> ---
>  mm/migrate.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 89 insertions(+), 1 deletion(-)

LGTM. Reviewed-by: Zi Yan <ziy@...dia.com>


—
Best Regards,
Yan, Zi

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