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Documentation/admin-guide/mm/pagemap.rst: drop "Using pagemap to do something useful"

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That example was added in 2008.  In 2015, we restricted access to the PFNs
in the pagemap to CAP_SYS_ADMIN, making that approach quite less usable.

It's 2024 now, and using that racy and low-lewel mechanism to calculate
the USS should not be considered a good example anymore.  /proc/$pid/smaps
and /proc/$pid/smaps_rollup can do a much better job without any of that
low-level handling.

Let's just drop that example.

Link: https://lkml.kernel.org/r/20240607122357.115423-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Oscar Salvador <osalvador@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2024-06-07 14:23:57 +02:00 committed by Andrew Morton
parent cdd9a571b7
commit 478fd0d8ec
1 changed files with 0 additions and 21 deletions
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Documentation/admin-guide/mm/pagemap.rst
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@ -173,27 +173,6 @@ LRU related page flags
The page-types tool in the tools/mm directory can be used to query the
above flags.
Using pagemap to do something useful
====================================
The general procedure for using pagemap to find out about a process' memory
usage goes like this:
1. Read ``/proc/pid/maps`` to determine which parts of the memory space are
mapped to what.
2. Select the maps you are interested in -- all of them, or a particular
library, or the stack or the heap, etc.
3. Open ``/proc/pid/pagemap`` and seek to the pages you would like to examine.
4. Read a u64 for each page from pagemap.
5. Open ``/proc/kpagecount`` and/or ``/proc/kpageflags``. For each PFN you
just read, seek to that entry in the file, and read the data you want.
For example, to find the "unique set size" (USS), which is the amount of
memory that a process is using that is not shared with any other process,
you can go through every map in the process, find the PFNs, look those up
in kpagecount, and tally up the number of pages that are only referenced
once.
Exceptions for Shared Memory
============================