Re: [PATCH v2 3/7] mm/swap: Use local_lock for protection

Sebastian Andrzej Siewior
2020-05-25T17:08:00Z

On 2020-05-25 08:44:36 [+0200], Ingo Molnar wrote:
> s/lru_rotate_pvecs
> /lru_rotate_pvec
>
> it's a single pagevec, using plural is confusing when reading the
> code.

right. It had the _pvecs from the beginning so I assumed it is because
it is per-CPU.

With all you suggestions I'm at:

diff --git a/include/linux/swap.h b/include/linux/swap.h
index e1bbf7a16b276..25181d2dd0b9f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -337,6 +337,7 @@ extern void activate_page(struct page *);
extern void mark_page_accessed(struct page *);
extern void lru_add_drain(void);
extern void lru_add_drain_cpu(int cpu);
+extern void lru_add_drain_cpu_zone(struct zone *zone);
extern void lru_add_drain_all(void);
extern void rotate_reclaimable_page(struct page *page);
extern void deactivate_file_page(struct page *page);
diff --git a/mm/compaction.c b/mm/compaction.c
index 46f0fcc93081e..c9d659e6a02c5 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2243,15 +2243,11 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
* would succeed.
*/
if (cc->order > 0 && last_migrated_pfn) {
- int cpu;
unsigned long current_block_start =
block_start_pfn(cc->migrate_pfn, cc->order);

if (last_migrated_pfn < current_block_start) {
- cpu = get_cpu();
- lru_add_drain_cpu(cpu);
- drain_local_pages(cc->zone);
- put_cpu();
+ lru_add_drain_cpu_zone(cc->zone);
/* No more flushing until we migrate again */
last_migrated_pfn = 0;
}
diff --git a/mm/swap.c b/mm/swap.c
index bf9a79fed62d7..0ac463d44cff4 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -35,6 +35,7 @@
#include <linux/uio.h>
#include <linux/hugetlb.h>
#include <linux/page_idle.h>
+#include <linux/local_lock.h>

#include "internal.h"

@@ -44,14 +45,32 @@
/* How many pages do we try to swap or page in/out together? */
int page_cluster;

-static DEFINE_PER_CPU(struct pagevec, lru_add_pvec);
-static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
-static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs);
-static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
-static DEFINE_PER_CPU(struct pagevec, lru_lazyfree_pvecs);
+/* Protecting only lru_rotate.pvec which requires disabling interrupts */
+struct lru_rotate {
+ local_lock_t lock;
+ struct pagevec pvec;
+};
+static DEFINE_PER_CPU(struct lru_rotate, lru_rotate) = {
+ .lock = INIT_LOCAL_LOCK(lock),
+};
+
+/*
+ * The following struct pagevec are grouped together because they are protected
+ * by disabling preemption (and interrupts remain enabled).
+ */
+struct lru_pvecs {
+ local_lock_t lock;
+ struct pagevec lru_add;
+ struct pagevec lru_deactivate_file;
+ struct pagevec lru_deactivate;
+ struct pagevec lru_lazyfree;
#ifdef CONFIG_SMP
-static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
+ struct pagevec activate_page;
#endif
+};
+static DEFINE_PER_CPU(struct lru_pvecs, lru_pvecs) = {
+ .lock = INIT_LOCAL_LOCK(lock),
+};

/*
* This path almost never happens for VM activity - pages are normally
@@ -254,11 +273,11 @@ void rotate_reclaimable_page(struct page *page)
unsigned long flags;

get_page(page);
- local_irq_save(flags);
- pvec = this_cpu_ptr(&lru_rotate_pvecs);
+ local_lock_irqsave(&lru_rotate.lock, flags);
+ pvec = this_cpu_ptr(&lru_rotate.pvec);
if (!pagevec_add(pvec, page) || PageCompound(page))
pagevec_move_tail(pvec);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&lru_rotate.lock, flags);
}
}

@@ -293,7 +312,7 @@ static void __activate_page(struct page *page, struct lruvec *lruvec,
#ifdef CONFIG_SMP
static void activate_page_drain(int cpu)
{
- struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
+ struct pagevec *pvec = &per_cpu(lru_pvecs.activate_page, cpu);

if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, __activate_page, NULL);
@@ -301,19 +320,21 @@ static void activate_page_drain(int cpu)

static bool need_activate_page_drain(int cpu)
{
- return pagevec_count(&per_cpu(activate_page_pvecs, cpu)) != 0;
+ return pagevec_count(&per_cpu(lru_pvecs.activate_page, cpu)) != 0;
}

void activate_page(struct page *page)
{
page = compound_head(page);
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
- struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
+ struct pagevec *pvec;

+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.activate_page);
get_page(page);
if (!pagevec_add(pvec, page) || PageCompound(page))
pagevec_lru_move_fn(pvec, __activate_page, NULL);
- put_cpu_var(activate_page_pvecs);
+ local_unlock(&lru_pvecs.lock);
}
}

@@ -335,9 +356,12 @@ void activate_page(struct page *page)

static void __lru_cache_activate_page(struct page *page)
{
- struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
+ struct pagevec *pvec;
int i;

+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.lru_add);
+
/*
* Search backwards on the optimistic assumption that the page being
* activated has just been added to this pagevec. Note that only
@@ -357,7 +381,7 @@ static void __lru_cache_activate_page(struct page *page)
}
}

- put_cpu_var(lru_add_pvec);
+ local_unlock(&lru_pvecs.lock);
}

/*
@@ -385,7 +409,7 @@ void mark_page_accessed(struct page *page)
} else if (!PageActive(page)) {
/*
* If the page is on the LRU, queue it for activation via
- * activate_page_pvecs. Otherwise, assume the page is on a
+ * lru_pvecs.activate_page. Otherwise, assume the page is on a
* pagevec, mark it active and it'll be moved to the active
* LRU on the next drain.
*/
@@ -404,12 +428,14 @@ EXPORT_SYMBOL(mark_page_accessed);

static void __lru_cache_add(struct page *page)
{
- struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
+ struct pagevec *pvec;

+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.lru_add);
get_page(page);
if (!pagevec_add(pvec, page) || PageCompound(page))
__pagevec_lru_add(pvec);
- put_cpu_var(lru_add_pvec);
+ local_unlock(&lru_pvecs.lock);
}

/**
@@ -593,30 +619,30 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
*/
void lru_add_drain_cpu(int cpu)
{
- struct pagevec *pvec = &per_cpu(lru_add_pvec, cpu);
+ struct pagevec *pvec = &per_cpu(lru_pvecs.lru_add, cpu);

if (pagevec_count(pvec))
__pagevec_lru_add(pvec);

- pvec = &per_cpu(lru_rotate_pvecs, cpu);
+ pvec = &per_cpu(lru_rotate.pvec, cpu);
if (pagevec_count(pvec)) {
unsigned long flags;

/* No harm done if a racing interrupt already did this */
- local_irq_save(flags);
+ local_lock_irqsave(&lru_rotate.lock, flags);
pagevec_move_tail(pvec);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&lru_rotate.lock, flags);
}

- pvec = &per_cpu(lru_deactivate_file_pvecs, cpu);
+ pvec = &per_cpu(lru_pvecs.lru_deactivate_file, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);

- pvec = &per_cpu(lru_deactivate_pvecs, cpu);
+ pvec = &per_cpu(lru_pvecs.lru_deactivate, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);

- pvec = &per_cpu(lru_lazyfree_pvecs, cpu);
+ pvec = &per_cpu(lru_pvecs.lru_lazyfree, cpu);
if (pagevec_count(pvec))
pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);

@@ -641,11 +667,14 @@ void deactivate_file_page(struct page *page)
return;

if (likely(get_page_unless_zero(page))) {
- struct pagevec *pvec = &get_cpu_var(lru_deactivate_file_pvecs);
+ struct pagevec *pvec;
+
+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate_file);

if (!pagevec_add(pvec, page) || PageCompound(page))
pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);
- put_cpu_var(lru_deactivate_file_pvecs);
+ local_unlock(&lru_pvecs.lock);
}
}

@@ -660,12 +689,14 @@ void deactivate_file_page(struct page *page)
void deactivate_page(struct page *page)
{
if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
- struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
+ struct pagevec *pvec;

+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.lru_deactivate);
get_page(page);
if (!pagevec_add(pvec, page) || PageCompound(page))
pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
- put_cpu_var(lru_deactivate_pvecs);
+ local_unlock(&lru_pvecs.lock);
}
}

@@ -680,19 +711,30 @@ void mark_page_lazyfree(struct page *page)
{
if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
!PageSwapCache(page) && !PageUnevictable(page)) {
- struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs);
+ struct pagevec *pvec;

+ local_lock(&lru_pvecs.lock);
+ pvec = this_cpu_ptr(&lru_pvecs.lru_lazyfree);
get_page(page);
if (!pagevec_add(pvec, page) || PageCompound(page))
pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);
- put_cpu_var(lru_lazyfree_pvecs);
+ local_unlock(&lru_pvecs.lock);
}
}

void lru_add_drain(void)
{
- lru_add_drain_cpu(get_cpu());
- put_cpu();
+ local_lock(&lru_pvecs.lock);
+ lru_add_drain_cpu(smp_processor_id());
+ local_unlock(&lru_pvecs.lock);
+}
+
+void lru_add_drain_cpu_zone(struct zone *zone)
+{
+ local_lock(&lru_pvecs.lock);
+ lru_add_drain_cpu(smp_processor_id());
+ drain_local_pages(zone);
+ local_unlock(&lru_pvecs.lock);
}

#ifdef CONFIG_SMP
@@ -743,11 +785,11 @@ void lru_add_drain_all(void)
for_each_online_cpu(cpu) {
struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);

- if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
- pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
- pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) ||
- pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
- pagevec_count(&per_cpu(lru_lazyfree_pvecs, cpu)) ||
+ if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
+ pagevec_count(&per_cpu(lru_rotate.pvec, cpu)) ||
+ pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) ||
+ pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) ||
+ pagevec_count(&per_cpu(lru_pvecs.lru_lazyfree, cpu)) ||
need_activate_page_drain(cpu)) {
INIT_WORK(work, lru_add_drain_per_cpu);
queue_work_on(cpu, mm_percpu_wq, work);
--
2.27.0.rc0

> Thanks,
>
> Ingo

Sebastian