[RFC v2 8/9] mm/damon/debugfs: Support physical memory monitoring

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

This commit makes the debugfs interface to support the physical memory
monitoring, in addition to the virtual memory monitoring.

Users can do the physical memory monitoring by writing a special
keyword, 'paddr\n' to the 'pids' debugfs file.  Then, DAMON will check
the special keyword and configure the callbacks of the monitoring
context for the debugfs user for physical memory.  This will internally
add one fake monitoring target process, which has pid as -1.

Unlike the virtual memory monitoring, DAMON debugfs will not
automatically set the monitoring target region.  Therefore, users should
also set the monitoring target address region using the 'init_regions'
debugfs file.  While doing this, the 'pid' in the input should be '-1'.

Finally, the physical memory monitoring will not automatically
terminated because it has fake monitoring target process.  The user
should explicitly turn off the monitoring by writing 'off' to the
'monitor_on' debugfs file.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 mm/damon.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/mm/damon.c b/mm/damon.c
index 6a5c6d540580..7361d5885118 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -1263,6 +1263,9 @@ static bool kdamond_need_stop(struct damon_ctx *ctx)
 		return true;
 
 	damon_for_each_task(t, ctx) {
+		if (t->pid == -1)
+			return false;
+
 		task = damon_get_task_struct(t);
 		if (task) {
 			put_task_struct(task);
@@ -1796,6 +1799,23 @@ static ssize_t debugfs_pids_write(struct file *file,
 	if (ret < 0)
 		goto out;
 
+	if (!strncmp(kbuf, "paddr\n", count)) {
+		/* Configure the context for physical memory monitoring */
+		ctx->init_target_regions = kdamond_init_phys_regions;
+		ctx->update_target_regions = kdamond_update_phys_regions;
+		ctx->prepare_access_checks = kdamond_prepare_phys_access_checks;
+		ctx->check_accesses = kdamond_check_phys_accesses;
+
+		/* Set the fake target task pid as -1 */
+		snprintf(kbuf, count, "-1");
+	} else {
+		/* Configure the context for virtual memory monitoring */
+		ctx->init_target_regions = kdamond_init_vm_regions;
+		ctx->update_target_regions = kdamond_update_vm_regions;
+		ctx->prepare_access_checks = kdamond_prepare_vm_access_checks;
+		ctx->check_accesses = kdamond_check_vm_accesses;
+	}
+
 	targets = str_to_pids(kbuf, ret, &nr_targets);
 	if (!targets) {
 		ret = -ENOMEM;
-- 
2.17.1