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

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Message-ID: <CA+CK2bCFgwLXp=pUTKezWtRoCKiDC41DqGXx_kahg0UcB53sPw@mail.gmail.com>
Date:   Thu, 2 Nov 2023 11:11:03 -0400
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Sourav Panda <souravpanda@...gle.com>, corbet@....net,
        rafael@...nel.org, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com, muchun.song@...ux.dev, rppt@...nel.org,
        david@...hat.com, rdunlap@...radead.org, chenlinxuan@...ontech.com,
        yang.yang29@....com.cn, tomas.mudrunka@...il.com,
        bhelgaas@...gle.com, ivan@...udflare.com, yosryahmed@...gle.com,
        hannes@...xchg.org, shakeelb@...gle.com,
        kirill.shutemov@...ux.intel.com, wangkefeng.wang@...wei.com,
        adobriyan@...il.com, vbabka@...e.cz, Liam.Howlett@...cle.com,
        surenb@...gle.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, willy@...radead.org, weixugc@...gle.com
Subject: Re: [PATCH v5 1/1] mm: report per-page metadata information

On Thu, Nov 2, 2023 at 10:29 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Nov 02, 2023 at 10:24:04AM -0400, Pasha Tatashin wrote:
> > On Thu, Nov 2, 2023 at 1:42 AM Greg KH <gregkh@...uxfoundation.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.
>
> And that is wrong, and again, an abuse of sysfs, please do not continue
> to add to it, that will only cause problems.
>
> > 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
>
> All of the fields should be individual files, please start adding them
> if you want to add new items, I do not want to see additional abuse here

Sounds good, in our next patch version we will create a new file under
nodeN/ to contain per-page metadata overhead, and add an ABI doc file
for it.

Thanks,
Pasha