[RFC PATCH 2/2] mm: zsmalloc: use the shrinker reclaim budget

From: Xueyuan Chen <[email protected]>

The zsmalloc shrinker currently compacts the whole pool for every scan,
which can do much more work than reclaim requires.

Use the requested page count as the compaction goal and continue later
scans from the previous position.

Signed-off-by: Xueyuan Chen <[email protected]>
---
 mm/zsmalloc.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 334d24093c64..aa5900ce2620 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -217,6 +217,8 @@ struct zs_pool {
 	/* protect zspage migration/compaction */
 	rwlock_t lock;
 	atomic_t compaction_in_progress;
+	/* next class shrinker triggered compaction */
+	unsigned int compact_cursor;
 };
 
 static inline void zpdesc_set_first(struct zpdesc *zpdesc)
@@ -1949,9 +1951,10 @@ static unsigned long __zs_compact(struct zs_pool *pool,
 }
 
 static unsigned long zs_compact_pool(struct zs_pool *pool,
-					unsigned long max_pages)
+					unsigned long max_pages,
+					bool use_cursor)
 {
-	int i;
+	unsigned int index, nr_scanned;
 	struct size_class *class;
 	unsigned long pages_freed = 0;
 
@@ -1967,15 +1970,19 @@ static unsigned long zs_compact_pool(struct zs_pool *pool,
 	if (atomic_xchg(&pool->compaction_in_progress, 1))
 		return 0;
 
-	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
-		class = pool->size_class[i];
-		if (class->index != i)
-			continue;
-		pages_freed += __zs_compact(pool, class,
-					max_pages - pages_freed);
+	index = use_cursor ? pool->compact_cursor : ZS_SIZE_CLASSES - 1;
+	for (nr_scanned = ZS_SIZE_CLASSES; nr_scanned; nr_scanned--) {
+		class = pool->size_class[index];
+		if (class->index == index)
+			pages_freed += __zs_compact(pool, class,
+						max_pages - pages_freed);
+		index = index ? index - 1 : ZS_SIZE_CLASSES - 1;
 		if (pages_freed >= max_pages)
 			break;
 	}
+	if (use_cursor)
+		pool->compact_cursor = index;
+
 	atomic_long_add(pages_freed, &pool->stats.pages_compacted);
 	atomic_set(&pool->compaction_in_progress, 0);
 
@@ -1984,7 +1991,7 @@ static unsigned long zs_compact_pool(struct zs_pool *pool,
 
 unsigned long zs_compact(struct zs_pool *pool)
 {
-	return zs_compact_pool(pool, ULONG_MAX);
+	return zs_compact_pool(pool, ULONG_MAX, false);
 }
 EXPORT_SYMBOL_GPL(zs_compact);
 
@@ -2000,12 +2007,7 @@ static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
 	unsigned long pages_freed;
 	struct zs_pool *pool = shrinker->private_data;
 
-	/*
-	 * Compact classes and calculate compaction delta.
-	 * Can run concurrently with a manually triggered
-	 * (by user) compaction.
-	 */
-	pages_freed = zs_compact(pool);
+	pages_freed = zs_compact_pool(pool, sc->nr_to_scan, true);
 
 	return pages_freed ? pages_freed : SHRINK_STOP;
 }
@@ -2094,6 +2096,7 @@ struct zs_pool *zs_create_pool(const char *name)
 	init_deferred_free(pool);
 	rwlock_init(&pool->lock);
 	atomic_set(&pool->compaction_in_progress, 0);
+	pool->compact_cursor = ZS_SIZE_CLASSES - 1;
 
 	pool->name = kstrdup(name, GFP_KERNEL);
 	if (!pool->name)
-- 
2.47.3