[PATCH v2] psi: move PF_MEMSTALL out of task->flags

[PATCH v2] psi: move PF_MEMSTALL out of task->flags

[Yafang Shao]

The task->flags is a 32-bits flag, in which 31 bits have already been
consumed. So it is hardly to introduce other new per process flag.
Currently there're still enough spaces in the bit-field section of
task_struct, so we can define the memstall state as a single bit in
task_struct instead.
This patch also removes an out-of-date comment pointed by Matthew.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/linux/sched.h |  6 ++++--
 kernel/sched/psi.c    | 12 ++++++------
 kernel/sched/stats.h  | 10 +++++-----
 3 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0d84f8f..c429e97 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -783,9 +783,12 @@ struct task_struct {
 	unsigned			frozen:1;
 #endif
 #ifdef CONFIG_BLK_CGROUP
-	/* to be used once the psi infrastructure lands upstream. */
 	unsigned			use_memdelay:1;
 #endif
+#ifdef CONFIG_PSI
+	/* Stalled due to lack of memory */
+	unsigned			in_memstall:1;
+#endif
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
@@ -1490,7 +1493,6 @@ static inline int is_global_init(struct task_struct *tsk)
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
-#define PF_MEMSTALL		0x01000000	/* Stalled due to lack of memory */
 #define PF_UMH			0x02000000	/* I'm an Usermodehelper process */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 517e371..d068e83 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -817,17 +817,17 @@ void psi_memstall_enter(unsigned long *flags)
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	*flags = current->flags & PF_MEMSTALL;
+	*flags = current->in_memstall;
 	if (*flags)
 		return;
 	/*
-	 * PF_MEMSTALL setting & accounting needs to be atomic wrt
+	 * in_memstall setting & accounting needs to be atomic wrt
 	 * changes to the task's scheduling state, otherwise we can
 	 * race with CPU migration.
 	 */
 	rq = this_rq_lock_irq(&rf);
 
-	current->flags |= PF_MEMSTALL;
+	current->in_memstall = 1;
 	psi_task_change(current, 0, TSK_MEMSTALL);
 
 	rq_unlock_irq(rq, &rf);
@@ -850,13 +850,13 @@ void psi_memstall_leave(unsigned long *flags)
 	if (*flags)
 		return;
 	/*
-	 * PF_MEMSTALL clearing & accounting needs to be atomic wrt
+	 * in_memstall clearing & accounting needs to be atomic wrt
 	 * changes to the task's scheduling state, otherwise we could
 	 * race with CPU migration.
 	 */
 	rq = this_rq_lock_irq(&rf);
 
-	current->flags &= ~PF_MEMSTALL;
+	current->in_memstall = 0;
 	psi_task_change(current, TSK_MEMSTALL, 0);
 
 	rq_unlock_irq(rq, &rf);
@@ -920,7 +920,7 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 	else if (task->in_iowait)
 		task_flags = TSK_IOWAIT;
 
-	if (task->flags & PF_MEMSTALL)
+	if (task->in_memstall)
 		task_flags |= TSK_MEMSTALL;
 
 	if (task_flags)
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index ba683fe..199e304 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -70,7 +70,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 		return;
 
 	if (!wakeup || p->sched_psi_wake_requeue) {
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
 		if (p->sched_psi_wake_requeue)
 			p->sched_psi_wake_requeue = 0;
@@ -90,7 +90,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
 		return;
 
 	if (!sleep) {
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			clear |= TSK_MEMSTALL;
 	} else {
 		if (p->in_iowait)
@@ -109,14 +109,14 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
 	 * deregister its sleep-persistent psi states from the old
 	 * queue, and let psi_enqueue() know it has to requeue.
 	 */
-	if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
+	if (unlikely(p->in_iowait || p->in_memstall)) {
 		struct rq_flags rf;
 		struct rq *rq;
 		int clear = 0;
 
 		if (p->in_iowait)
 			clear |= TSK_IOWAIT;
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			clear |= TSK_MEMSTALL;
 
 		rq = __task_rq_lock(p, &rf);
@@ -131,7 +131,7 @@ static inline void psi_task_tick(struct rq *rq)
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	if (unlikely(rq->curr->flags & PF_MEMSTALL))
+	if (unlikely(rq->curr->in_memstall))
 		psi_memstall_tick(rq->curr, cpu_of(rq));
 }
 #else /* CONFIG_PSI */
-- 
1.8.3.1

[tip: sched/core] psi: Move PF_MEMSTALL out of task->flags

[tip-bot2 for Yafang Shao]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     1066d1b6974e095d5a6c472ad9180a957b496cd6
Gitweb:        https://git.kernel.org/tip/1066d1b6974e095d5a6c472ad9180a957b496cd6
Author:        Yafang Shao <laoar.shao@gmail.com>
AuthorDate:    Mon, 16 Mar 2020 21:28:05 -04:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 20 Mar 2020 13:06:19 +01:00

psi: Move PF_MEMSTALL out of task->flags

The task->flags is a 32-bits flag, in which 31 bits have already been
consumed. So it is hardly to introduce other new per process flag.
Currently there're still enough spaces in the bit-field section of
task_struct, so we can define the memstall state as a single bit in
task_struct instead.
This patch also removes an out-of-date comment pointed by Matthew.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/1584408485-1921-1-git-send-email-laoar.shao@gmail.com
---
 include/linux/sched.h |  6 ++++--
 kernel/sched/psi.c    | 12 ++++++------
 kernel/sched/stats.h  | 10 +++++-----
 3 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2e9199b..09bddd9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -785,9 +785,12 @@ struct task_struct {
 	unsigned			frozen:1;
 #endif
 #ifdef CONFIG_BLK_CGROUP
-	/* to be used once the psi infrastructure lands upstream. */
 	unsigned			use_memdelay:1;
 #endif
+#ifdef CONFIG_PSI
+	/* Stalled due to lack of memory */
+	unsigned			in_memstall:1;
+#endif
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
@@ -1480,7 +1483,6 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
-#define PF_MEMSTALL		0x01000000	/* Stalled due to lack of memory */
 #define PF_UMH			0x02000000	/* I'm an Usermodehelper process */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 955a124..8f45cdb 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -865,17 +865,17 @@ void psi_memstall_enter(unsigned long *flags)
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	*flags = current->flags & PF_MEMSTALL;
+	*flags = current->in_memstall;
 	if (*flags)
 		return;
 	/*
-	 * PF_MEMSTALL setting & accounting needs to be atomic wrt
+	 * in_memstall setting & accounting needs to be atomic wrt
 	 * changes to the task's scheduling state, otherwise we can
 	 * race with CPU migration.
 	 */
 	rq = this_rq_lock_irq(&rf);
 
-	current->flags |= PF_MEMSTALL;
+	current->in_memstall = 1;
 	psi_task_change(current, 0, TSK_MEMSTALL);
 
 	rq_unlock_irq(rq, &rf);
@@ -898,13 +898,13 @@ void psi_memstall_leave(unsigned long *flags)
 	if (*flags)
 		return;
 	/*
-	 * PF_MEMSTALL clearing & accounting needs to be atomic wrt
+	 * in_memstall clearing & accounting needs to be atomic wrt
 	 * changes to the task's scheduling state, otherwise we could
 	 * race with CPU migration.
 	 */
 	rq = this_rq_lock_irq(&rf);
 
-	current->flags &= ~PF_MEMSTALL;
+	current->in_memstall = 0;
 	psi_task_change(current, TSK_MEMSTALL, 0);
 
 	rq_unlock_irq(rq, &rf);
@@ -970,7 +970,7 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 	} else if (task->in_iowait)
 		task_flags = TSK_IOWAIT;
 
-	if (task->flags & PF_MEMSTALL)
+	if (task->in_memstall)
 		task_flags |= TSK_MEMSTALL;
 
 	if (task_flags)
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 1339f5b..33d0daf 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -70,7 +70,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 		return;
 
 	if (!wakeup || p->sched_psi_wake_requeue) {
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
 		if (p->sched_psi_wake_requeue)
 			p->sched_psi_wake_requeue = 0;
@@ -90,7 +90,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
 		return;
 
 	if (!sleep) {
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			clear |= TSK_MEMSTALL;
 	} else {
 		/*
@@ -117,14 +117,14 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
 	 * deregister its sleep-persistent psi states from the old
 	 * queue, and let psi_enqueue() know it has to requeue.
 	 */
-	if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
+	if (unlikely(p->in_iowait || p->in_memstall)) {
 		struct rq_flags rf;
 		struct rq *rq;
 		int clear = 0;
 
 		if (p->in_iowait)
 			clear |= TSK_IOWAIT;
-		if (p->flags & PF_MEMSTALL)
+		if (p->in_memstall)
 			clear |= TSK_MEMSTALL;
 
 		rq = __task_rq_lock(p, &rf);
@@ -149,7 +149,7 @@ static inline void psi_task_tick(struct rq *rq)
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	if (unlikely(rq->curr->flags & PF_MEMSTALL))
+	if (unlikely(rq->curr->in_memstall))
 		psi_memstall_tick(rq->curr, cpu_of(rq));
 }
 #else /* CONFIG_PSI */

Re: [tip: sched/core] psi: Move PF_MEMSTALL out of task->flags

[Yafang Shao]

On Fri, Mar 20, 2020 at 8:58 PM tip-bot2 for Yafang Shao
<tip-bot2@linutronix.de> wrote:
>
> The following commit has been merged into the sched/core branch of tip:
>
> Commit-ID:     1066d1b6974e095d5a6c472ad9180a957b496cd6
> Gitweb:        https://git.kernel.org/tip/1066d1b6974e095d5a6c472ad9180a957b496cd6
> Author:        Yafang Shao <laoar.shao@gmail.com>
> AuthorDate:    Mon, 16 Mar 2020 21:28:05 -04:00
> Committer:     Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Fri, 20 Mar 2020 13:06:19 +01:00
>
> psi: Move PF_MEMSTALL out of task->flags
>
> The task->flags is a 32-bits flag, in which 31 bits have already been
> consumed. So it is hardly to introduce other new per process flag.
> Currently there're still enough spaces in the bit-field section of
> task_struct, so we can define the memstall state as a single bit in
> task_struct instead.
> This patch also removes an out-of-date comment pointed by Matthew.
>
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Link: https://lkml.kernel.org/r/1584408485-1921-1-git-send-email-laoar.shao@gmail.com
> ---
>  include/linux/sched.h |  6 ++++--
>  kernel/sched/psi.c    | 12 ++++++------
>  kernel/sched/stats.h  | 10 +++++-----
>  3 files changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 2e9199b..09bddd9 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -785,9 +785,12 @@ struct task_struct {
>         unsigned                        frozen:1;
>  #endif
>  #ifdef CONFIG_BLK_CGROUP
> -       /* to be used once the psi infrastructure lands upstream. */
>         unsigned                        use_memdelay:1;
>  #endif
> +#ifdef CONFIG_PSI
> +       /* Stalled due to lack of memory */
> +       unsigned                        in_memstall:1;
> +#endif
>
>         unsigned long                   atomic_flags; /* Flags requiring atomic access. */
>
> @@ -1480,7 +1483,6 @@ extern struct pid *cad_pid;
>  #define PF_KTHREAD             0x00200000      /* I am a kernel thread */
>  #define PF_RANDOMIZE           0x00400000      /* Randomize virtual address space */
>  #define PF_SWAPWRITE           0x00800000      /* Allowed to write to swap */
> -#define PF_MEMSTALL            0x01000000      /* Stalled due to lack of memory */
>  #define PF_UMH                 0x02000000      /* I'm an Usermodehelper process */
>  #define PF_NO_SETAFFINITY      0x04000000      /* Userland is not allowed to meddle with cpus_mask */
>  #define PF_MCE_EARLY           0x08000000      /* Early kill for mce process policy */
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 955a124..8f45cdb 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -865,17 +865,17 @@ void psi_memstall_enter(unsigned long *flags)
>         if (static_branch_likely(&psi_disabled))
>                 return;
>
> -       *flags = current->flags & PF_MEMSTALL;
> +       *flags = current->in_memstall;
>         if (*flags)
>                 return;
>         /*
> -        * PF_MEMSTALL setting & accounting needs to be atomic wrt
> +        * in_memstall setting & accounting needs to be atomic wrt
>          * changes to the task's scheduling state, otherwise we can
>          * race with CPU migration.
>          */
>         rq = this_rq_lock_irq(&rf);
>
> -       current->flags |= PF_MEMSTALL;
> +       current->in_memstall = 1;
>         psi_task_change(current, 0, TSK_MEMSTALL);
>
>         rq_unlock_irq(rq, &rf);
> @@ -898,13 +898,13 @@ void psi_memstall_leave(unsigned long *flags)
>         if (*flags)
>                 return;
>         /*
> -        * PF_MEMSTALL clearing & accounting needs to be atomic wrt
> +        * in_memstall clearing & accounting needs to be atomic wrt
>          * changes to the task's scheduling state, otherwise we could
>          * race with CPU migration.
>          */
>         rq = this_rq_lock_irq(&rf);
>
> -       current->flags &= ~PF_MEMSTALL;
> +       current->in_memstall = 0;
>         psi_task_change(current, TSK_MEMSTALL, 0);
>
>         rq_unlock_irq(rq, &rf);
> @@ -970,7 +970,7 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
>         } else if (task->in_iowait)
>                 task_flags = TSK_IOWAIT;
>
> -       if (task->flags & PF_MEMSTALL)
> +       if (task->in_memstall)
>                 task_flags |= TSK_MEMSTALL;
>
>         if (task_flags)
> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
> index 1339f5b..33d0daf 100644
> --- a/kernel/sched/stats.h
> +++ b/kernel/sched/stats.h
> @@ -70,7 +70,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
>                 return;
>
>         if (!wakeup || p->sched_psi_wake_requeue) {
> -               if (p->flags & PF_MEMSTALL)
> +               if (p->in_memstall)
>                         set |= TSK_MEMSTALL;
>                 if (p->sched_psi_wake_requeue)
>                         p->sched_psi_wake_requeue = 0;
> @@ -90,7 +90,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
>                 return;
>
>         if (!sleep) {
> -               if (p->flags & PF_MEMSTALL)
> +               if (p->in_memstall)
>                         clear |= TSK_MEMSTALL;
>         } else {
>                 /*
> @@ -117,14 +117,14 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
>          * deregister its sleep-persistent psi states from the old
>          * queue, and let psi_enqueue() know it has to requeue.
>          */
> -       if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
> +       if (unlikely(p->in_iowait || p->in_memstall)) {
>                 struct rq_flags rf;
>                 struct rq *rq;
>                 int clear = 0;
>
>                 if (p->in_iowait)
>                         clear |= TSK_IOWAIT;
> -               if (p->flags & PF_MEMSTALL)
> +               if (p->in_memstall)
>                         clear |= TSK_MEMSTALL;
>
>                 rq = __task_rq_lock(p, &rf);
> @@ -149,7 +149,7 @@ static inline void psi_task_tick(struct rq *rq)
>         if (static_branch_likely(&psi_disabled))
>                 return;
>
> -       if (unlikely(rq->curr->flags & PF_MEMSTALL))
> +       if (unlikely(rq->curr->in_memstall))
>                 psi_memstall_tick(rq->curr, cpu_of(rq));
>  }
>  #else /* CONFIG_PSI */

+ Andrew

Hi Peter,

This patch was aleady added into Andrew's -mm tree.[1]
I'm not sure whether that could cause merge conflict when both of them
are merged into Linus's tree.

[1]. https://marc.info/?l=linux-mm-commits&m=158456557519886&w=2

-- 
Yafang Shao
DiDi

Re: [tip: sched/core] psi: Move PF_MEMSTALL out of task->flags

[Andrew Morton]

On Sat, 21 Mar 2020 10:47:05 +0800 Yafang Shao <laoar.shao@gmail.com> wrote:

> This patch was aleady added into Andrew's -mm tree.[1]
> I'm not sure whether that could cause merge conflict when both of them
> are merged into Linus's tree.
> 

That's OK - if a patch turns up in someone else's -next tree I'll drop
my copy.  Usually after checking that the other copy was the same
version (it usually is) and after checking whether it has up to date
cc:stable and review/ack tags (it usually doesn't!).

Re: [tip: sched/core] psi: Move PF_MEMSTALL out of task->flags

[Yafang Shao]

On Sat, Mar 21, 2020 at 10:55 AM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Sat, 21 Mar 2020 10:47:05 +0800 Yafang Shao <laoar.shao@gmail.com> wrote:
>
> > This patch was aleady added into Andrew's -mm tree.[1]
> > I'm not sure whether that could cause merge conflict when both of them
> > are merged into Linus's tree.
> >
>
> That's OK - if a patch turns up in someone else's -next tree I'll drop
> my copy.  Usually after checking that the other copy was the same
> version (it usually is) and after checking whether it has up to date
> cc:stable and review/ack tags (it usually doesn't!).
>

Got it.
Thanks for your explanation.

-- 
Yafang Shao
DiDi