drop_caches: re-enable message after disabling

PATCH Superseded Ruiwu Chen 4 participants 5 messages Feb 16, 2025 – Feb 21, 2025

Subsystems (4)

Documentation VFS MM core Proc sysctl

lore

Share & tools

lore

Ruiwu Chen

author

2025-02-16 10:18 UTC #0 lore raw

PATCH 1/1 drop_caches: re-enable message after disabling

When 'echo 4 > /proc/sys/vm/drop_caches' the message is disabled, but there is no interface to enable the message, only by restarting the way, so I want to add the 'echo 0 > /proc/sys/vm/drop_caches' way to enabled the message again.

Signed-off-by Ruiwu Chen <[email protected]>

---
 fs/drop_caches.c | 7 +++++--
 kernel/sysctl.c  | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

fs/drop_caches.c +5 -2

index d45ef541d848..c90cfaf9756d 100644
@@ -57,7 +57,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	if (ret)
 		return ret;
 	if (write) {
-		static int stfu;
+		static bool stfu;
 
 		if (sysctl_drop_caches & 1) {
 			lru_add_drain_all();

@@ -73,7 +73,10 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		if (sysctl_drop_caches == 0)
+			stfu = false;
+		else if (sysctl_drop_caches == 4)
+			stfu = true;
 	}
 	return 0;
 }

kernel/sysctl.c +1 -1

index cb57da499ebb..f2e06e074724 100644
@@ -2088,7 +2088,7 @@ static const struct ctl_table vm_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0200,
 		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_FOUR,
 	},
 	{

Signature · 1 line

2.27.0

Darrick J. Wong

2025-02-16 17:07 UTC #1 lore raw

Quoted 4 lines · Ruiwu Chen

When 'echo 4 > /proc/sys/vm/drop_caches' the message is disabled, but there is no interface to enable the message, only by restarting the way, so I want to add the 'echo 0 > /proc/sys/vm/drop_caches' way to enabled the message again.

Please update Documentation/ to note this new API.

--D

Quoted 48 lines

Signed-off-by Ruiwu Chen <[email protected]>

---
 fs/drop_caches.c | 7 +++++--
 kernel/sysctl.c  | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

fs/drop_caches.c +5 -2

index d45ef541d848..c90cfaf9756d 100644
@@ -57,7 +57,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	if (ret)
 		return ret;
 	if (write) {
-		static int stfu;
+		static bool stfu;
 
 		if (sysctl_drop_caches & 1) {
 			lru_add_drain_all();

@@ -73,7 +73,10 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		if (sysctl_drop_caches == 0)
+			stfu = false;
+		else if (sysctl_drop_caches == 4)
+			stfu = true;
 	}
 	return 0;
 }

kernel/sysctl.c +1 -1

index cb57da499ebb..f2e06e074724 100644
@@ -2088,7 +2088,7 @@ static const struct ctl_table vm_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0200,
 		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_FOUR,
 	},
 	{

Signature · 1 line

2.27.0

Christian Brauner

maintainer

2025-02-17 08:28 UTC #2 lore raw

In reply to Ruiwu Chen

Quoted 16 lines · Ruiwu Chen

When 'echo 4 > /proc/sys/vm/drop_caches' the message is disabled, but there is no interface to enable the message, only by restarting the way, so I want to add the 'echo 0 > /proc/sys/vm/drop_caches' way to enabled the message again.
Signed-off-by Ruiwu Chen <[email protected]>
---
 fs/drop_caches.c | 7 +++++--
 kernel/sysctl.c  | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)
fs/drop_caches.c +0 -0
index d45ef541d848..c90cfaf9756d 100644

fs/drop_caches.c int drop_caches_sysctl_handler(const struct ctl_table *table, int write, · line 60

Quoted 5 lines

fs/drop_caches.c +1 -1

@@ -57,7 +57,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	if (ret)
 		return ret;
 	if (write) {
-		static int stfu;
+		static bool stfu;

Please the change and change that to something explicitly like "silent".

Quoted 31 lines

fs/drop_caches.c +4 -1

 		if (sysctl_drop_caches & 1) {
 			lru_add_drain_all();

@@ -73,7 +73,10 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		if (sysctl_drop_caches == 0)
+			stfu = false;
+		else if (sysctl_drop_caches == 4)
+			stfu = true;
 	}
 	return 0;
 }

kernel/sysctl.c +1 -1

index cb57da499ebb..f2e06e074724 100644
@@ -2088,7 +2088,7 @@ static const struct ctl_table vm_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0200,
 		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_FOUR,
 	},
 	{

Signature · 1 line

2.27.0

Ruiwu Chen

author

2025-02-20 13:19 UTC #3 lore raw

PATCH v2 1/1 drop_caches: re-enable message after disabling

In reply to Ruiwu Chen

Signed-off-by Ruiwu Chen <[email protected]>

---
v2: - updated Documentation/ to note this new API.
- renamed the variable.

 Documentation/admin-guide/sysctl/vm.rst | 11 ++++++++++-
 fs/drop_caches.c                        |  9 ++++++---
 kernel/sysctl.c                         |  2 +-
 3 files changed, 17 insertions(+), 5 deletions(-)

Documentation/admin-guide/sysctl/vm.rst +10 -1

index f48eaa98d22d..1b9ae9bc6cf9 100644
@@ -266,7 +266,16 @@ used::
 	cat (1234): drop_caches: 3
 
 These are informational only.  They do not mean that anything is wrong
-with your system.  To disable them, echo 4 (bit 2) into drop_caches.
+with your system.
+
+To disable informational::
+
+    echo 4 > /proc/sys/vm/drop_caches
+
+To enable informational::
+
+    echo 0 > /proc/sys/vm/drop_caches
+
 
 enable_soft_offline
 ===================

fs/drop_caches.c +6 -3

index d45ef541d848..5d02c1d99d9f 100644
@@ -57,7 +57,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	if (ret)
 		return ret;
 	if (write) {
-		static int stfu;
+		static bool silent;
 
 		if (sysctl_drop_caches & 1) {
 			lru_add_drain_all();

@@ -68,12 +68,15 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 			drop_slab();
 			count_vm_event(DROP_SLAB);
 		}
-		if (!stfu) {
+		if (!silent) {
 			pr_info("%s (%d): drop_caches: %d\n",
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		if (sysctl_drop_caches == 0)
+			silent = false;
+		else if (sysctl_drop_caches == 4)
+			silent = true;
 	}
 	return 0;
 }

kernel/sysctl.c +1 -1

index cb57da499ebb..f2e06e074724 100644
@@ -2088,7 +2088,7 @@ static const struct ctl_table vm_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0200,
 		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_FOUR,
 	},
 	{

Signature · 1 line

2.27.0

Joel Granados

maintainer

2025-02-21 08:52 UTC #4 lore raw

In reply to Ruiwu Chen

Quoted 41 lines · Ruiwu Chen

Signed-off-by Ruiwu Chen <[email protected]>

---
 fs/drop_caches.c | 7 +++++--
 kernel/sysctl.c  | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

fs/drop_caches.c +5 -2

index d45ef541d848..c90cfaf9756d 100644
@@ -57,7 +57,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 	if (ret)
 		return ret;
 	if (write) {
-		static int stfu;
+		static bool stfu;
 
 		if (sysctl_drop_caches & 1) {
 			lru_add_drain_all();

@@ -73,7 +73,10 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		if (sysctl_drop_caches == 0)
+			stfu = false;
+		else if (sysctl_drop_caches == 4)
+			stfu = true;
 	}
 	return 0;
 }

kernel/sysctl.c +0 -0

index cb57da499ebb..f2e06e074724 100644

kernel/sysctl.c static const struct ctl_table vm_table[] = { · line 2092

Quoted 6 lines

kernel/sysctl.c +1 -1

@@ -2088,7 +2088,7 @@ static const struct ctl_table vm_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0200,
 		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_FOUR,

note that vm_table will no longer exist in the next version. Please rebase this on top of sysctl-next

Best

Quoted 5 lines

kernel/sysctl.c +0 -0
 	},
 	{
Signature · 1 line
2.27.0

Signature · 1 line

Joel Granados