Re: [PATCH v5 1/1] mm: report per-page metadata information

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Thu, Nov 2, 2023 at 1:42 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Nov 01, 2023 at 04:08:16PM -0700, Sourav Panda wrote:
> > Adds a new per-node PageMetadata field to
> > /sys/devices/system/node/nodeN/meminfo
>
> No, this file is already an abuse of sysfs and we need to get rid of it
> (it has multiple values in one file.)  Please do not add to the
> nightmare by adding new values.

Hi Greg,

Today, nodeN/meminfo is a counterpart of /proc/meminfo, they contain
almost identical fields, but show node-wide and system-wide views.

Since per-page metadata is added into /proc/meminfo, it is logical to
add into nodeN/meminfo, some nodes can have more or less struct page
data based on size of the node, and also the way memory is configured,
such as use of vmemamp optimization etc, therefore this information is
useful to users.

I am not aware of any example of where a system-wide field from
/proc/meminfo is represented as a separate sysfs file under node0/. If
nodeN/meminfo is ever broken down into separate files it will affect
all the fields in it the same way with or without per-page metadata

> Also, even if you did want to do this, you didn't document it properly
> in Documentation/ABI/ :(

 The documentation for the fields in nodeN/meminfo is only specified
in  Documentation/filesystems/proc.rst, there is no separate sysfs
Documentation for the fields in this file, we could certainly add
that.

Thank you,
Pasha