[PATCH v3 2/2] lru: allow large batched add large folio to lru list

[Yin Fengwei <fengwei.yin@intel.com>]

Currently, large folio is not batched added to lru list. Which
cause high lru lock contention after enable large folio for
anonymous mapping.

Running page_fault1 of will-it-scale + order 2 folio with 96
processes on Ice Lake 48C/96T, the lru lock contention could
be around 64%:
-   64.31%     0.23%  page_fault1_pro  [kernel.kallsyms]           [k] folio_lruvec_lock_irqsave
   - 64.07% folio_lruvec_lock_irqsave
      + 64.01% _raw_spin_lock_irqsave

With this patch, the lru lock contention dropped to 43% with same
testing:
-   42.67%     0.19%  page_fault1_pro  [kernel.kallsyms]           [k] folio_lruvec_lock_irqsave
   - 42.48% folio_lruvec_lock_irqsave
      + 42.42% _raw_spin_lock_irqsave

Reported-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
---
 include/linux/pagevec.h | 46 ++++++++++++++++++++++++++++++++++++++---
 mm/mlock.c              |  7 +++----
 mm/swap.c               |  3 +--
 3 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index f582f7213ea5..9479b7b50bc6 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -10,6 +10,7 @@
 #define _LINUX_PAGEVEC_H
 
 #include <linux/xarray.h>
+#include <linux/mm.h>
 
 /* 15 pointers + header align the pagevec structure to a power of two */
 #define PAGEVEC_SIZE	15
@@ -22,6 +23,7 @@ struct address_space;
 struct pagevec {
 	unsigned char nr;
 	bool percpu_pvec_drained;
+	unsigned short nr_pages;
 	struct page *pages[PAGEVEC_SIZE];
 };
 
@@ -30,12 +32,14 @@ void __pagevec_release(struct pagevec *pvec);
 static inline void pagevec_init(struct pagevec *pvec)
 {
 	pvec->nr = 0;
+	pvec->nr_pages = 0;
 	pvec->percpu_pvec_drained = false;
 }
 
 static inline void pagevec_reinit(struct pagevec *pvec)
 {
 	pvec->nr = 0;
+	pvec->nr_pages = 0;
 }
 
 static inline unsigned pagevec_count(struct pagevec *pvec)
@@ -54,7 +58,12 @@ static inline unsigned pagevec_space(struct pagevec *pvec)
 static inline unsigned pagevec_add(struct pagevec *pvec, struct page *page)
 {
 	pvec->pages[pvec->nr++] = page;
-	return pagevec_space(pvec);
+	pvec->nr_pages += compound_nr(page);
+
+	if (pvec->nr_pages > PAGEVEC_SIZE)
+		return 0;
+	else
+		return pagevec_space(pvec);
 }
 
 static inline void pagevec_release(struct pagevec *pvec)
@@ -75,6 +84,7 @@ static inline void pagevec_release(struct pagevec *pvec)
 struct folio_batch {
 	unsigned char nr;
 	bool percpu_pvec_drained;
+	unsigned short nr_pages;
 	struct folio *folios[PAGEVEC_SIZE];
 };
 
@@ -92,12 +102,14 @@ static_assert(offsetof(struct pagevec, pages) ==
 static inline void folio_batch_init(struct folio_batch *fbatch)
 {
 	fbatch->nr = 0;
+	fbatch->nr_pages = 0;
 	fbatch->percpu_pvec_drained = false;
 }
 
 static inline void folio_batch_reinit(struct folio_batch *fbatch)
 {
 	fbatch->nr = 0;
+	fbatch->nr_pages = 0;
 }
 
 static inline unsigned int folio_batch_count(struct folio_batch *fbatch)
@@ -110,6 +122,32 @@ static inline unsigned int fbatch_space(struct folio_batch *fbatch)
 	return PAGEVEC_SIZE - fbatch->nr;
 }
 
+/**
+ * folio_batch_add_nr_pages() - Add a folio to a batch.
+ * @fbatch: The folio batch.
+ * @folio: The folio to add.
+ * @nr_pages: The number of pages added to batch.
+ *
+ * The folio is added to the end of the batch.
+ * The batch must have previously been initialised using folio_batch_init().
+ *
+ * Return: The number of slots still available.
+ * Note: parameter folio may not be direct reference to folio and can't
+ *       use folio_nr_pages(folio).
+ *       Currently, this function is only called in mlock.c.
+ */
+static inline unsigned folio_batch_add_nr_pages(struct folio_batch *fbatch,
+		struct folio *folio, unsigned int nr_pages)
+{
+	fbatch->folios[fbatch->nr++] = folio;
+	fbatch->nr_pages += nr_pages;
+
+	if (fbatch->nr_pages > PAGEVEC_SIZE)
+		return 0;
+	else
+		return fbatch_space(fbatch);
+}
+
 /**
  * folio_batch_add() - Add a folio to a batch.
  * @fbatch: The folio batch.
@@ -123,8 +161,10 @@ static inline unsigned int fbatch_space(struct folio_batch *fbatch)
 static inline unsigned folio_batch_add(struct folio_batch *fbatch,
 		struct folio *folio)
 {
-	fbatch->folios[fbatch->nr++] = folio;
-	return fbatch_space(fbatch);
+	unsigned int nr_pages;
+
+	nr_pages = xa_is_value(folio) ? 1 : folio_nr_pages(folio);
+	return folio_batch_add_nr_pages(fbatch, folio, nr_pages);
 }
 
 static inline void folio_batch_release(struct folio_batch *fbatch)
diff --git a/mm/mlock.c b/mm/mlock.c
index 617469fce96d..6de3e6d4639f 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -243,19 +243,18 @@ bool need_mlock_drain(int cpu)
 void mlock_folio(struct folio *folio)
 {
 	struct folio_batch *fbatch;
+	unsigned int nr_pages = folio_nr_pages(folio);
 
 	local_lock(&mlock_fbatch.lock);
 	fbatch = this_cpu_ptr(&mlock_fbatch.fbatch);
 
 	if (!folio_test_set_mlocked(folio)) {
-		int nr_pages = folio_nr_pages(folio);
-
 		zone_stat_mod_folio(folio, NR_MLOCK, nr_pages);
 		__count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
 	}
 
 	folio_get(folio);
-	if (!folio_batch_add(fbatch, mlock_lru(folio)) ||
+	if (!folio_batch_add_nr_pages(fbatch, mlock_lru(folio), nr_pages) ||
 	    folio_test_large(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
@@ -278,7 +277,7 @@ void mlock_new_folio(struct folio *folio)
 	__count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
 
 	folio_get(folio);
-	if (!folio_batch_add(fbatch, mlock_new(folio)) ||
+	if (!folio_batch_add_nr_pages(fbatch, mlock_new(folio), nr_pages) ||
 	    folio_test_large(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
diff --git a/mm/swap.c b/mm/swap.c
index 57cb01b042f6..0f8554aeb338 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -228,8 +228,7 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
 static void folio_batch_add_and_move(struct folio_batch *fbatch,
 		struct folio *folio, move_fn_t move_fn)
 {
-	if (folio_batch_add(fbatch, folio) && !folio_test_large(folio) &&
-	    !lru_cache_disabled())
+	if (folio_batch_add(fbatch, folio) && !lru_cache_disabled())
 		return;
 	folio_batch_move_lru(fbatch, move_fn);
 }
-- 
2.34.1