linux-kernel - Re: [PATCH 6/6] mm/migrate: export whether or not node is toptier in sysf

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Message-ID: <CAHbLzkpNBRdhBewviYWke+dgERjKi_nhEdTU5V75Sr92yp2K3w@mail.gmail.com>
Date:   Fri, 22 Apr 2022 10:37:00 -0700
From:   Yang Shi <shy828301@...il.com>
To:     linux-mm@...ck.org, mhocko@...nel.org, akpm@...ux-foundation.org,
        rientjes@...gle.com, yosryahmed@...gle.com, hannes@...xchg.org,
        shakeelb@...gle.com, dave.hansen@...ux.intel.com,
        tim.c.chen@...ux.intel.com, roman.gushchin@...ux.dev,
        gthelen@...gle.com, a.manzanares@...sung.com,
        heekwon.p@...sung.com, gim.jongmin@...sung.com,
        linux-kernel@...r.kernel.org, jvgediya@...ux.ibm.com,
        ying.huang@...el.com
Subject: Re: [PATCH 6/6] mm/migrate: export whether or not node is toptier in sysf

On Sat, Apr 16, 2022 at 8:49 PM Davidlohr Bueso <dave@...olabs.net> wrote:
>
>
>
> This allows userspace to know if the node is considered fast
> memory (with CPUs attached to it). While this can be already
> derived without a new file, this helps further encapsulate the
> concept.
>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> ---
> Resending, just noticed this oatch was never posted.
>
>   Documentation/ABI/stable/sysfs-devices-node |  6 ++++++
>   drivers/base/node.c                         | 13 +++++++++++++
>   2 files changed, 19 insertions(+)
>
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index f620c6ae013c..1c21c3985535 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -198,3 +198,9 @@ Date:               April 2022
>   Contact:      Davidlohr Bueso <dave@...olabs.net>
>   Description:
>                 Shows nodes within the next tier of slower memory below this node.
> +
> +What:          /sys/devices/system/node/nodeX/memory_toptier
> +Date:          April 2022
> +Contact:       Davidlohr Bueso <dave@...olabs.net>
> +Description:
> +               Node is attached to fast memory or not.
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index ab4bae777535..b9de5b0360f2 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -598,12 +598,25 @@ static ssize_t node_read_demotion_path(struct device *dev,
>   }
>   static DEVICE_ATTR(demotion_path, 0444, node_read_demotion_path, NULL);
>
> +static ssize_t node_read_memory_toptier(struct device *dev,
> +                                    struct device_attribute *attr, char *buf)
> +{
> +       int nid = dev->id;
> +       int len = 0;
> +
> +       len += sysfs_emit_at(buf, len, "%d\n", !!node_is_toptier(nid));

It is not guaranteed. Some hardware configurations have cpuless DRAM
nodes, but they should be treated as top tier nodes IMHO. Please see
https://lore.kernel.org/linux-mm/20220413092206.73974-1-jvgediya@linux.ibm.com/

> +
> +       return len;
> +}
> +static DEVICE_ATTR(memory_toptier, 0444, node_read_memory_toptier, NULL);
> +
>   static struct attribute *node_dev_attrs[] = {
>         &dev_attr_meminfo.attr,
>         &dev_attr_numastat.attr,
>         &dev_attr_distance.attr,
>         &dev_attr_vmstat.attr,
>         &dev_attr_demotion_path.attr,
> +       &dev_attr_memory_toptier.attr,
>         NULL
>   };
>
> --
> 2.26.2
>