[PATCH] mm/damon/core: introduce damon_set_target_pid()

[PATCH] mm/damon/core: introduce damon_set_target_pid()

[Enze Li]

The logic that finds the struct pid for a given pid number and assigns
it to a damon_target is duplicated in multiple places.  Including
damon_sysfs_add_target() of mm/damon/sysfs.c and the start functions
of the two sample modules, samples/damon/wsse.c and
samples/damon/prcl.c.  Add a function that does the work, and replace
the duplicated code in the places with calls to the function.

Signed-off-by: Enze Li <lienze@kylinos.cn>
---
 include/linux/damon.h |  1 +
 mm/damon/core.c       | 12 ++++++++++++
 mm/damon/sysfs.c      |  6 ++----
 samples/damon/prcl.c  |  5 +----
 samples/damon/wsse.c  |  5 +----
 5 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 0c8b7ddef9ab..a937aa55170b 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1054,6 +1054,7 @@ int damos_commit_quota_goals(struct damos_quota *dst, struct damos_quota *src);
 
 struct damon_target *damon_new_target(void);
 void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
+int damon_set_target_pid(struct damon_target *t, int pid);
 bool damon_targets_empty(struct damon_ctx *ctx);
 void damon_free_target(struct damon_target *t);
 void damon_destroy_target(struct damon_target *t, struct damon_ctx *ctx);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 644daf5a1656..82b196407ae8 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -10,6 +10,7 @@
 #include <linux/kthread.h>
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
+#include <linux/pid.h>
 #include <linux/psi.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -795,6 +796,17 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
 	list_add_tail(&t->list, &ctx->adaptive_targets);
 }
 
+/*
+ * Assign the struct pid of the given pid number to the given target.
+ */
+int damon_set_target_pid(struct damon_target *t, int pid)
+{
+	t->pid = find_get_pid(pid);
+	if (!t->pid)
+		return -EINVAL;
+	return 0;
+}
+
 bool damon_targets_empty(struct damon_ctx *ctx)
 {
 	return list_empty(&ctx->adaptive_targets);
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index e3858ffab4b2..3c81b4c91ac0 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -3,7 +3,6 @@
  * DAMON sysfs Interface
  */
 
-#include <linux/pid.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 
@@ -2035,9 +2034,8 @@ static int damon_sysfs_add_target(struct damon_sysfs_target *sys_target,
 		return -ENOMEM;
 	damon_add_target(ctx, t);
 	if (damon_target_has_pid(ctx)) {
-		t->pid = find_get_pid(sys_target->pid);
-		if (!t->pid)
-			/* caller will destroy targets */
+		/* caller will destroy targets */
+		if (damon_set_target_pid(t, sys_target->pid))
 			return -EINVAL;
 	}
 	t->obsolete = sys_target->obsolete;
diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c
index 842099bd6228..83ddf12811d5 100644
--- a/samples/damon/prcl.c
+++ b/samples/damon/prcl.c
@@ -32,7 +32,6 @@ module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
 MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_PRCL");
 
 static struct damon_ctx *ctx;
-static struct pid *target_pidp;
 
 static int damon_sample_prcl_repeat_call_fn(void *data)
 {
@@ -79,12 +78,10 @@ static int damon_sample_prcl_start(void)
 		return -ENOMEM;
 	}
 	damon_add_target(ctx, target);
-	target_pidp = find_get_pid(target_pid);
-	if (!target_pidp) {
+	if (damon_set_target_pid(target, target_pid)) {
 		damon_destroy_ctx(ctx);
 		return -EINVAL;
 	}
-	target->pid = target_pidp;
 
 	scheme = damon_new_scheme(
 			&(struct damos_access_pattern) {
diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
index 37fd5da20158..53944aea8428 100644
--- a/samples/damon/wsse.c
+++ b/samples/damon/wsse.c
@@ -33,7 +33,6 @@ module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
 MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_WSSE");
 
 static struct damon_ctx *ctx;
-static struct pid *target_pidp;
 
 static int damon_sample_wsse_repeat_call_fn(void *data)
 {
@@ -79,12 +78,10 @@ static int damon_sample_wsse_start(void)
 		return -ENOMEM;
 	}
 	damon_add_target(ctx, target);
-	target_pidp = find_get_pid(target_pid);
-	if (!target_pidp) {
+	if (damon_set_target_pid(target, target_pid)) {
 		damon_destroy_ctx(ctx);
 		return -EINVAL;
 	}
-	target->pid = target_pidp;
 
 	err = damon_start(&ctx, 1, true);
 	if (err) {
-- 
2.43.0

Re: [PATCH] mm/damon/core: introduce damon_set_target_pid()

[sashiko-bot]

> The logic that finds the struct pid for a given pid number and assigns
> it to a damon_target is duplicated in multiple places.  Including
> damon_sysfs_add_target() of mm/damon/sysfs.c and the start functions
> of the two sample modules, samples/damon/wsse.c and
> samples/damon/prcl.c.  Add a function that does the work, and replace
> the duplicated code in the places with calls to the function.
> 
> Signed-off-by: Enze Li <lienze@kylinos.cn>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260817125319.888994-1-lienze@kylinos.cn?part=1

Re: [PATCH] mm/damon/core: introduce damon_set_target_pid()

[Gutierrez Asier]

Hi Enze,

On 8/17/2026 3:53 PM, Enze Li wrote:
> The logic that finds the struct pid for a given pid number and assigns
> it to a damon_target is duplicated in multiple places.  Including
> damon_sysfs_add_target() of mm/damon/sysfs.c and the start functions
> of the two sample modules, samples/damon/wsse.c and
> samples/damon/prcl.c.  Add a function that does the work, and replace
> the duplicated code in the places with calls to the function.
> 
> Signed-off-by: Enze Li <lienze@kylinos.cn>
> ---
>  include/linux/damon.h |  1 +
>  mm/damon/core.c       | 12 ++++++++++++
>  mm/damon/sysfs.c      |  6 ++----
>  samples/damon/prcl.c  |  5 +----
>  samples/damon/wsse.c  |  5 +----
>  5 files changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 0c8b7ddef9ab..a937aa55170b 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -1054,6 +1054,7 @@ int damos_commit_quota_goals(struct damos_quota *dst, struct damos_quota *src);
>  
>  struct damon_target *damon_new_target(void);
>  void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
> +int damon_set_target_pid(struct damon_target *t, int pid);
>  bool damon_targets_empty(struct damon_ctx *ctx);
>  void damon_free_target(struct damon_target *t);
>  void damon_destroy_target(struct damon_target *t, struct damon_ctx *ctx);
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 644daf5a1656..82b196407ae8 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -10,6 +10,7 @@
>  #include <linux/kthread.h>
>  #include <linux/memcontrol.h>
>  #include <linux/mm.h>
> +#include <linux/pid.h>
>  #include <linux/psi.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> @@ -795,6 +796,17 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
>  	list_add_tail(&t->list, &ctx->adaptive_targets);
>  }
>  
> +/*
> + * Assign the struct pid of the given pid number to the given target.
> + */
This method is simple enough. Do we really need a comment?
> +int damon_set_target_pid(struct damon_target *t, int pid)
> +{
> +	t->pid = find_get_pid(pid);
> +	if (!t->pid)
> +		return -EINVAL;
> +	return 0;
> +}
> +
>  bool damon_targets_empty(struct damon_ctx *ctx)
>  {
>  	return list_empty(&ctx->adaptive_targets);
> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index e3858ffab4b2..3c81b4c91ac0 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c
> @@ -3,7 +3,6 @@
>   * DAMON sysfs Interface
>   */
>  
> -#include <linux/pid.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
>  
> @@ -2035,9 +2034,8 @@ static int damon_sysfs_add_target(struct damon_sysfs_target *sys_target,
>  		return -ENOMEM;
>  	damon_add_target(ctx, t);
>  	if (damon_target_has_pid(ctx)) {
> -		t->pid = find_get_pid(sys_target->pid);
> -		if (!t->pid)
> -			/* caller will destroy targets */
> +		/* caller will destroy targets */
> +		if (damon_set_target_pid(t, sys_target->pid))
>  			return -EINVAL;
>  	}
>  	t->obsolete = sys_target->obsolete;
> diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c
> index 842099bd6228..83ddf12811d5 100644
> --- a/samples/damon/prcl.c
> +++ b/samples/damon/prcl.c
> @@ -32,7 +32,6 @@ module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
>  MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_PRCL");
>  
>  static struct damon_ctx *ctx;
> -static struct pid *target_pidp;
>  
>  static int damon_sample_prcl_repeat_call_fn(void *data)
>  {
> @@ -79,12 +78,10 @@ static int damon_sample_prcl_start(void)
>  		return -ENOMEM;
>  	}
>  	damon_add_target(ctx, target);
> -	target_pidp = find_get_pid(target_pid);
> -	if (!target_pidp) {
> +	if (damon_set_target_pid(target, target_pid)) {
>  		damon_destroy_ctx(ctx);
>  		return -EINVAL;
>  	}
> -	target->pid = target_pidp;
>  
>  	scheme = damon_new_scheme(
>  			&(struct damos_access_pattern) {
> diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
> index 37fd5da20158..53944aea8428 100644
> --- a/samples/damon/wsse.c
> +++ b/samples/damon/wsse.c
> @@ -33,7 +33,6 @@ module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
>  MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_WSSE");
>  
>  static struct damon_ctx *ctx;
> -static struct pid *target_pidp;
>  
>  static int damon_sample_wsse_repeat_call_fn(void *data)
>  {
> @@ -79,12 +78,10 @@ static int damon_sample_wsse_start(void)
>  		return -ENOMEM;
>  	}
>  	damon_add_target(ctx, target);
> -	target_pidp = find_get_pid(target_pid);
> -	if (!target_pidp) {
> +	if (damon_set_target_pid(target, target_pid)) {
>  		damon_destroy_ctx(ctx);
>  		return -EINVAL;
>  	}
> -	target->pid = target_pidp;
>  
>  	err = damon_start(&ctx, 1, true);
>  	if (err) {

Otherwise, it looks like a nice patch.

-- 
Asier Gutierrez
Huawei

Re: [PATCH] mm/damon/core: introduce damon_set_target_pid()

[SJ Park]

On Mon, 17 Aug 2026 20:53:19 +0800 Enze Li <lienze@kylinos.cn> wrote:

> The logic that finds the struct pid for a given pid number and assigns
> it to a damon_target is duplicated in multiple places.  Including
> damon_sysfs_add_target() of mm/damon/sysfs.c and the start functions
> of the two sample modules, samples/damon/wsse.c and
> samples/damon/prcl.c.  Add a function that does the work, and replace
> the duplicated code in the places with calls to the function.

Looks good to me, thank you!

> 
> Signed-off-by: Enze Li <lienze@kylinos.cn>

Reviewed-by: SJ Park <sj@kernel.org>

This patch is applied to damon/next [1] tree.  If this patch is not added to
mm.git in short term, I will ask mm.git maintainer (Andrew Morton) to pick
this.  Note that we are in the middle of the merge window.  The action would be
made only after the end of the window.  So, no action from your side is needed
for now.  If it seems I also forgot doing that or you cannot wait for my
action, please feel free to directly ask that to Andrew.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees


Thanks,
SJ

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