[PATCH] Make SPLIT_RSS_COUNTING configurable

Daniel Colascione
2019-10-02T20:25:13Z

Using the new config option, users can disable SPLIT_RSS_COUNTING to
get increased accuracy in user-visible mm counters.

Signed-off-by: Daniel Colascione <dancol@google.com>
---
include/linux/mm.h | 4 ++--
include/linux/mm_types_task.h | 5 ++---
include/linux/sched.h | 2 +-
kernel/fork.c | 2 +-
mm/Kconfig | 11 +++++++++++
mm/memory.c | 6 +++---
6 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cc292273e6ba..221395de3cb4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1637,7 +1637,7 @@ static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
{
long val = atomic_long_read(&mm->rss_stat.count[member]);

-#ifdef SPLIT_RSS_COUNTING
+#ifdef CONFIG_SPLIT_RSS_COUNTING
/*
* counter is updated in asynchronous manner and may go to minus.
* But it's never be expected number for users.
@@ -1723,7 +1723,7 @@ static inline void setmax_mm_hiwater_rss(unsigned long *maxrss,
*maxrss = hiwater_rss;
}

-#if defined(SPLIT_RSS_COUNTING)
+#ifdef CONFIG_SPLIT_RSS_COUNTING
void sync_mm_rss(struct mm_struct *mm);
#else
static inline void sync_mm_rss(struct mm_struct *mm)
diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h
index c1bc6731125c..d2adc8057e65 100644
--- a/include/linux/mm_types_task.h
+++ b/include/linux/mm_types_task.h
@@ -48,14 +48,13 @@ enum {
NR_MM_COUNTERS
};

-#if USE_SPLIT_PTE_PTLOCKS && defined(CONFIG_MMU)
-#define SPLIT_RSS_COUNTING
+#ifdef CONFIG_SPLIT_RSS_COUNTING
/* per-thread cached information, */
struct task_rss_stat {
int events; /* for synchronization threshold */
int count[NR_MM_COUNTERS];
};
-#endif /* USE_SPLIT_PTE_PTLOCKS */
+#endif /* CONFIG_SPLIT_RSS_COUNTING */

struct mm_rss_stat {
atomic_long_t count[NR_MM_COUNTERS];
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2c2e56bd8913..22f354774540 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -729,7 +729,7 @@ struct task_struct {
/* Per-thread vma caching: */
struct vmacache vmacache;

-#ifdef SPLIT_RSS_COUNTING
+#ifdef CONFIG_SPLIT_RSS_COUNTING
struct task_rss_stat rss_stat;
#endif
int exit_state;
diff --git a/kernel/fork.c b/kernel/fork.c
index f9572f416126..fc5e0889922b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1917,7 +1917,7 @@ static __latent_entropy struct task_struct *copy_process(
p->vtime.state = VTIME_INACTIVE;
#endif

-#if defined(SPLIT_RSS_COUNTING)
+#ifdef CONFIG_SPLIT_RSS_COUNTING
memset(&p->rss_stat, 0, sizeof(p->rss_stat));
#endif

diff --git a/mm/Kconfig b/mm/Kconfig
index a5dae9a7eb51..372ef9449924 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -736,4 +736,15 @@ config ARCH_HAS_PTE_SPECIAL
config ARCH_HAS_HUGEPD
bool

+config SPLIT_RSS_COUNTING
+ bool "Per-thread mm counter caching"
+ depends on MMU
+ default y if NR_CPUS >= SPLIT_PTLOCK_CPUS
+ help
+ Cache mm counter updates in thread structures and
+ flush them to visible per-process statistics in batches.
+ Say Y here to slightly reduce cache contention in processes
+ with many threads at the expense of decreasing the accuracy
+ of memory statistics in /proc.
+
endmenu
diff --git a/mm/memory.c b/mm/memory.c
index b1ca51a079f2..bf557ed5ba23 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -141,7 +141,7 @@ static int __init init_zero_pfn(void)
core_initcall(init_zero_pfn);

-#if defined(SPLIT_RSS_COUNTING)
+#ifdef CONFIG_SPLIT_RSS_COUNTING

void sync_mm_rss(struct mm_struct *mm)
{
@@ -177,7 +177,7 @@ static void check_sync_rss_stat(struct task_struct *task)
if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
sync_mm_rss(task->mm);
}
-#else /* SPLIT_RSS_COUNTING */
+#else /* CONFIG_SPLIT_RSS_COUNTING */

#define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
#define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)
@@ -186,7 +186,7 @@ static void check_sync_rss_stat(struct task_struct *task)
{
}

-#endif /* SPLIT_RSS_COUNTING */
+#endif /* CONFIG_SPLIT_RSS_COUNTING */

/*
* Note: this doesn't free the actual pages themselves. That
--
2.23.0.581.g78d2f28ef7-goog