linux-kernel - Re: [PATCH v3 2/7] mm: demotion: Add new node state N_DEMOTION

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Date:   Fri, 22 Apr 2022 13:29:22 -0700
From:   Wei Xu <weixugc@...gle.com>
To:     Jagdish Gediya <jvgediya@...ux.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, baolin.wang@...ux.alibaba.com,
        dave.hansen@...ux.intel.com, ying.huang@...el.com,
        aneesh.kumar@...ux.ibm.com, shy828301@...il.com,
        gthelen@...gle.com, dan.j.williams@...el.com
Subject: Re: [PATCH v3 2/7] mm: demotion: Add new node state N_DEMOTION_TARGETS

On Fri, Apr 22, 2022 at 12:55 PM Jagdish Gediya <jvgediya@...ux.ibm.com> wrote:
>
> Some systems(e.g. PowerVM) have DRAM(fast memory) only NUMA node
> which are N_MEMORY as well as slow memory(persistent memory) only
> NUMA node which are also N_MEMORY. As the current demotion target
> finding algorithm works based on N_MEMORY and best distance, it can
> choose DRAM only NUMA node as demotion target instead of persistent
> memory node on such systems. If DRAM only NUMA node is filled with
> demoted pages then at some point new allocations can start falling
> to persistent memory, so basically cold pages are in fast memory
> (due to demotion) and new pages are in slow memory, this is why
> persistent memory nodes should be utilized for demotion and dram node
> should be avoided for demotion so that they can be used for new
> allocations.
>
> Add new state N_DEMOTION_TARGETS, node_states[N_DEMOTION_TARGETS]
> then can be used to hold the list of nodes which can be used
> as demotion targets, later patches in the series builds demotion
> targets based on nodes available in node_states[N_DEMOTION_TARGETS].
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Signed-off-by: Jagdish Gediya <jvgediya@...ux.ibm.com>
> ---
>  drivers/base/node.c      | 4 ++++
>  include/linux/nodemask.h | 1 +
>  2 files changed, 5 insertions(+)
>

Acked-by: Wei Xu <weixugc@...gle.com>

> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index ec8bb24a5a22..6eef22e6413e 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -1038,6 +1038,9 @@ static struct node_attr node_state_attr[] = {
>         [N_CPU] = _NODE_ATTR(has_cpu, N_CPU),
>         [N_GENERIC_INITIATOR] = _NODE_ATTR(has_generic_initiator,
>                                            N_GENERIC_INITIATOR),
> +       [N_DEMOTION_TARGETS] = _NODE_ATTR(demotion_targets,
> +                                         N_DEMOTION_TARGETS),
> +
>  };
>
>  static struct attribute *node_state_attrs[] = {
> @@ -1050,6 +1053,7 @@ static struct attribute *node_state_attrs[] = {
>         &node_state_attr[N_MEMORY].attr.attr,
>         &node_state_attr[N_CPU].attr.attr,
>         &node_state_attr[N_GENERIC_INITIATOR].attr.attr,
> +       &node_state_attr[N_DEMOTION_TARGETS].attr.attr,
>         NULL
>  };
>
> diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
> index 567c3ddba2c4..17844300fd57 100644
> --- a/include/linux/nodemask.h
> +++ b/include/linux/nodemask.h
> @@ -400,6 +400,7 @@ enum node_states {
>         N_MEMORY,               /* The node has memory(regular, high, movable) */
>         N_CPU,          /* The node has one or more cpus */
>         N_GENERIC_INITIATOR,    /* The node has one or more Generic Initiators */
> +       N_DEMOTION_TARGETS,     /* Nodes that should be considered as demotion targets */
>         NR_NODE_STATES
>  };
>
> --
> 2.35.1
>