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Subject[PATCH v2] psi: move PF_MEMSTALL out of task->flags
Date
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This patch also removes an out-of-date comment pointed by Matthew.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
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