mm: batch activate_page() to reduce lock contention

The zone->lru_lock is heavily contented in workload where activate_page()
is frequently used.  We could do batch activate_page() to reduce the lock
contention.  The batched pages will be added into zone list when the pool
is full or page reclaim is trying to drain them.

For example, in a 4 socket 64 CPU system, create a sparse file and 64
processes, processes shared map to the file.  Each process read access the
whole file and then exit.  The process exit will do unmap_vmas() and cause
a lot of activate_page() call.  In such workload, we saw about 58% total
time reduction with below patch.  Other workloads with a lot of
activate_page also benefits a lot too.

I tested some microbenchmarks:
case-anon-cow-rand-mt		0.58%
case-anon-cow-rand		-3.30%
case-anon-cow-seq-mt		-0.51%
case-anon-cow-seq		-5.68%
case-anon-r-rand-mt		0.23%
case-anon-r-rand		0.81%
case-anon-r-seq-mt		-0.71%
case-anon-r-seq			-1.99%
case-anon-rx-rand-mt		2.11%
case-anon-rx-seq-mt		3.46%
case-anon-w-rand-mt		-0.03%
case-anon-w-rand		-0.50%
case-anon-w-seq-mt		-1.08%
case-anon-w-seq			-0.12%
case-anon-wx-rand-mt		-5.02%
case-anon-wx-seq-mt		-1.43%
case-fork			1.65%
case-fork-sleep			-0.07%
case-fork-withmem		1.39%
case-hugetlb			-0.59%
case-lru-file-mmap-read-mt	-0.54%
case-lru-file-mmap-read		0.61%
case-lru-file-mmap-read-rand	-2.24%
case-lru-file-readonce		-0.64%
case-lru-file-readtwice		-11.69%
case-lru-memcg			-1.35%
case-mmap-pread-rand-mt		1.88%
case-mmap-pread-rand		-15.26%
case-mmap-pread-seq-mt		0.89%
case-mmap-pread-seq		-69.72%
case-mmap-xread-rand-mt		0.71%
case-mmap-xread-seq-mt		0.38%

The most significent are:
case-lru-file-readtwice		-11.69%
case-mmap-pread-rand		-15.26%
case-mmap-pread-seq		-69.72%

which use activate_page a lot.  others are basically variations because
each run has slightly difference.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 79 insertions, 11 deletions

diff --git a/mm/swap.c b/mm/swap.c
index ab498ea04ae3..bbc1ce9f9460 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -271,27 +271,94 @@ static void update_page_reclaim_stat(struct zone *zone, struct page *page,
 }
 
 /*
- * FIXME: speed this up?
+ * A page will go to active list either by activate_page or putback_lru_page.
+ * In the activate_page case, the page hasn't active bit set. The page might
+ * not in LRU list because it's isolated before it gets a chance to be moved to
+ * active list. The window is small because pagevec just stores several pages.
+ * For such case, we do nothing for such page.
+ * In the putback_lru_page case, the page isn't in lru list but has active
+ * bit set
  */
-void activate_page(struct page *page)
+static void __activate_page(struct page *page, void *arg)
 {
         struct zone *zone = page_zone(page);
+        int file = page_is_file_cache(page);
+        int lru = page_lru_base_type(page);
+        bool putback = !PageLRU(page);
 
-        spin_lock_irq(&zone->lru_lock);
-        if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
-                int file = page_is_file_cache(page);
-                int lru = page_lru_base_type(page);
+        /* The page is isolated before it's moved to active list */
+        if (!PageLRU(page) && !PageActive(page))
+                return;
+        if ((PageLRU(page) && PageActive(page)) || PageUnevictable(page))
+                return;
+
+        if (!putback)
                 del_page_from_lru_list(zone, page, lru);
+        else
+                SetPageLRU(page);
 
-                SetPageActive(page);
-                lru += LRU_ACTIVE;
-                add_page_to_lru_list(zone, page, lru);
-                __count_vm_event(PGACTIVATE);
+        SetPageActive(page);
+        lru += LRU_ACTIVE;
+        add_page_to_lru_list(zone, page, lru);
+
+        if (putback)
+                return;
+        __count_vm_event(PGACTIVATE);
+        update_page_reclaim_stat(zone, page, file, 1);
+}
+
+#ifdef CONFIG_SMP
+static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
+
+static void activate_page_drain(int cpu)
+{
+        struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
+
+        if (pagevec_count(pvec))
+                pagevec_lru_move_fn(pvec, __activate_page, NULL);
+}
+
+void activate_page(struct page *page)
+{
+        if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
+                struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
+
+                page_cache_get(page);
+                if (!pagevec_add(pvec, page))
+                        pagevec_lru_move_fn(pvec, __activate_page, NULL);
+                put_cpu_var(activate_page_pvecs);
+        }
+}
 
-                update_page_reclaim_stat(zone, page, file, 1);
+/* Caller should hold zone->lru_lock */
+int putback_active_lru_page(struct zone *zone, struct page *page)
+{
+        struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
+
+        if (!pagevec_add(pvec, page)) {
+                spin_unlock_irq(&zone->lru_lock);
+                pagevec_lru_move_fn(pvec, __activate_page, NULL);
+                spin_lock_irq(&zone->lru_lock);
         }
+        put_cpu_var(activate_page_pvecs);
+        return 1;
+}
+
+#else
+static inline void activate_page_drain(int cpu)
+{
+}
+
+void activate_page(struct page *page)
+{
+        struct zone *zone = page_zone(page);
+
+        spin_lock_irq(&zone->lru_lock);
+        if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page))
+                __activate_page(page, NULL);
         spin_unlock_irq(&zone->lru_lock);
 }
+#endif
 
 /*
  * Mark a page as having seen activity.
@@ -390,6 +457,7 @@ static void drain_cpu_pagevecs(int cpu)
                 pagevec_move_tail(pvec);
                 local_irq_restore(flags);
         }
+        activate_page_drain(cpu);
 }
 
 void lru_add_drain(void)