Re: [RFC v6 00/10] DAMON: Support Physical Memory Address Space Monitoring

[SeongJae Park <sjpark@amazon.com>]

On Wed, 5 Aug 2020 08:59:41 +0200 SeongJae Park <sjpark@amazon.com> wrote:

> From: SeongJae Park <sjpark@amazon.de>
> 
> Changes from Previous Version
> =============================
> 
> - paddr: Support nested iomem sections (Du Fan)
> - Rebase on v5.8
> 
> Introduction
> ============
> 
> DAMON[1] programming interface users can extend DAMON for any address space by
> configuring the address-space specific low level primitives with appropriate
> ones including their own implementations.  However, because the implementation
> for the virtual address space is only available now, the users should implement
> their own for other address spaces.  Worse yet, the user space users who rely
> on the debugfs interface and user space tool, cannot implement their own.
> 
> This patchset implements another reference implementation of the low level
> primitives for the physical memory address space.  With this change, hence, the
> kernel space users can monitor both the virtual and the physical address spaces
> by simply changing the configuration in the runtime.  Further, this patchset
> links the implementation to the debugfs interface and the user space tool for
> the user space users.
> 
> Note that the implementation supports only the user memory, as same to the idle
> page access tracking feature.
> 
> [1] https://lore.kernel.org/linux-mm/20200706115322.29598-1-sjpark@amazon.com/

This patchset doesn't works for physical address monitoring because I forgot
below patch.  Sorry for missing it.  Please apply it before you test this
patchset.  Or, you can clone the patch applied complete git tree:

    $ git clone git://github.com/sjp38/linux -b cdamon/rfc/v6.1

The web is also available:
https://github.com/sjp38/linux/releases/tag/cdamon/rfc/v6.1

The patch will be split and squashed in appropriate patch in the next spin.

=============================== >8 ===========================================
From edf6b586f4ac3f8f4d61ebde56d644422bd93bee Mon Sep 17 00:00:00 2001
From: SeongJae Park <sjpark@amazon.de>
Date: Thu, 6 Aug 2020 08:18:49 +0000
Subject: [PATCH] mm/damon: Fix paddr target id problem

The target id for 'paddr' is meaningless, but we set it as '-1' for fun
and smooth interaction with the user space interfaces.  However, the
target ids are 'unsigned long' and thus using '-1' makes no sense.  This
commit changes the fake number to another funny but unsigned number,
'42'.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 Documentation/admin-guide/mm/damon/usage.rst | 4 ++--
 mm/damon.c                                   | 2 +-
 tools/damon/_damon.py                        | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 88b8e9254a7e..3e2f1519c96a 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -334,12 +334,12 @@ check it again::
 Users can also monitor the physical memory address space of the system by
 writing a special keyword, "``paddr\n``" to the file.  Because physical address
 space monitoring doesn't support multiple targets, reading the file will show a
-fake value, ``-1``, as below::
+fake value, ``42``, as below::

     # cd <debugfs>/damon
     # echo paddr > target_ids
     # cat target_ids
-    -1
+    42

 Note that setting the target ids doesn't start the monitoring.

diff --git a/mm/damon.c b/mm/damon.c
index a9757a0e5cf7..66268cb45b51 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -2047,7 +2047,7 @@ static ssize_t debugfs_target_ids_write(struct file *file,
                ctx->target_valid = NULL;

                /* target id is meaningless here, but we set it just for fun */
-               snprintf(kbuf, count, "-1    ");
+               snprintf(kbuf, count, "42    ");
        } else {
                /* Configure the context for virtual memory monitoring */
                ctx->init_target_regions = kdamond_init_vm_regions;
diff --git a/tools/damon/_damon.py b/tools/damon/_damon.py
index cf14a0d59b94..6ff278117e84 100644
--- a/tools/damon/_damon.py
+++ b/tools/damon/_damon.py
@@ -28,7 +28,7 @@ def set_target(tid, init_regions=[]):
         return 0

     if tid == 'paddr':
-        tid = -1
+        tid = 42
     string = ' '.join(['%s %d %d' % (tid, r[0], r[1]) for r in init_regions])
     return subprocess.call('echo "%s" > %s' % (string, debugfs_init_regions),
             shell=True, executable='/bin/bash')
--
2.17.1