linux-kernel - Re: [PATCH v9 1/1] mm: report per-page metadata information

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Message-Id: <20240319143320.d1b1ef7f6fa77b748579ba59@linux-foundation.org>
Date: Tue, 19 Mar 2024 14:33:20 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Sourav Panda <souravpanda@...gle.com>
Cc: corbet@....net, gregkh@...uxfoundation.org, rafael@...nel.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, pasha.tatashin@...een.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 v9 1/1] mm: report per-page metadata information

On Tue, 20 Feb 2024 13:45:58 -0800 Sourav Panda <souravpanda@...gle.com> wrote:

> Adds two new per-node fields, namely nr_memmap and nr_memmap_boot,
> to /sys/devices/system/node/nodeN/vmstat and a global Memmap field
> to /proc/meminfo. This information can be used by users to see how
> much memory is being used by per-page metadata, which can vary
> depending on build configuration, machine architecture, and system
> use.

I yield to no man in my admiration of changelogging but boy, that's a
lot of changelogging.  Would it be possible to consolidate the [0/N]
coverletter and the [1/N] changelog into a single thing please?

>  Documentation/filesystems/proc.rst |  3 +++
>  fs/proc/meminfo.c                  |  4 ++++
>  include/linux/mmzone.h             |  4 ++++
>  include/linux/vmstat.h             |  4 ++++
>  mm/hugetlb_vmemmap.c               | 17 ++++++++++++----
>  mm/mm_init.c                       |  3 +++
>  mm/page_alloc.c                    |  1 +
>  mm/page_ext.c                      | 32 +++++++++++++++++++++---------
>  mm/sparse-vmemmap.c                |  8 ++++++++
>  mm/sparse.c                        |  7 ++++++-
>  mm/vmstat.c                        | 26 +++++++++++++++++++++++-
>  11 files changed, 94 insertions(+), 15 deletions(-)

And yet we offer the users basically no documentation.  The new sysfs
file should be documented under Documentation/ABI somewhere and
perhaps we could prepare some more expansive user-facing documentation
elsewhere?

I'd like to hear others' views on the overall usefulness/utility of this
change, please?