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Date: Tue, 11 Jun 2024 15:30:03 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Sourav Panda <souravpanda@google.com>
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Subject: Re: [PATCH v13] mm: report per-page metadata information
Message-Id: <20240611153003.9f1b701e0ed28b129325128a@linux-foundation.org>
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On Wed,  5 Jun 2024 22:27:51 +0000 Sourav Panda <souravpanda@google.com> wrote:

> Today, we do not have any observability of per-page metadata
> and how much it takes away from the machine capacity. Thus,
> we want to describe the amount of memory that is going towards
> per-page metadata, which can vary depending on build
> configuration, machine architecture, and system use.
> 
> This patch adds 2 fields to /proc/vmstat that can used as shown
> below:
> 
> Accounting per-page metadata allocated by boot-allocator:
> 	/proc/vmstat:nr_memmap_boot * PAGE_SIZE
> 
> Accounting per-page metadata allocated by buddy-allocator:
> 	/proc/vmstat:nr_memmap * PAGE_SIZE
> 
> Accounting total Perpage metadata allocated on the machine:
> 	(/proc/vmstat:nr_memmap_boot +
> 	 /proc/vmstat:nr_memmap) * PAGE_SIZE

Under what circumstances do these change?  Only hotplug?

It's nasty, but would it be sufficient to simply emit these numbers
into dmesg when they change?