Re: [v5 PATCH] arm64: mm: show direct mapping use in /proc/meminfo

On Thu, Jan 22, 2026 at 10:39:25AM +0530, Anshuman Khandual wrote:

Hello Yang,

On 07/01/26 5:59 AM, Yang Shi wrote:

quoted

Since commit a166563e7ec3 ("arm64: mm: support large block mapping when
rodata=full"), the direct mapping may be split on some machines instead
keeping static since boot. It makes more sense to show the direct mapping
use in /proc/meminfo than before.

I guess the direct mapping here refers to linear map ? IIUC it is called
direct map on x86 and linear map on arm64 platforms. Then should not it
be renamed as s/DirectMap/LinearMap instead ? This will align with names
from ptdump as well.

Before the above mentioned commit, linear could get altered with memory
hotplug and remove events as well.

quoted

This patch will make /proc/meminfo show the direct mapping use like the
below (4K base page size):
DirectMap4K:	   94792 kB
DirectMap64K:	  134208 kB
DirectMap2M:	 1173504 kB
DirectMap32M:	 5636096 kB
DirectMap1G:	529530880 kB

If /proc/meminfo interface is getting updated via  arch_report_meminfo()
why not add stats for all kernel virtual address space ranges including
vmemmap, vmalloc etc aka all address range headers in ptdump as many of
those could change during system runtime. What makes linear mapping any
special ?

tbh, I think compatability with x86 is a good argument in this case and
so the naming and formatting proposed by this patch makes sense to me.

I'm also not sure that it's particularly interesting to see these
rolled-up numbers for the vmalloc area. You really want information
about the area, so extending /proc/vmallocinfo to give information
about the granule size for each entry might be useful but I don't think
it should be part of this patch.

Will