[PATCH v3 12/14] mm, swap: cap xswap growth at nr_clusters

[Baoquan He]

Add si->nr_clusters as the ceiling for the cluster_info array's growth.
It starts at the whole address space, so nothing changes yet.

Signed-off-by: Baoquan He <hebaoquan@xxxxxxxxxx>
---
 include/linux/swap.h |  1 +
 mm/swapfile.c        | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 30642bb481df..9fe82d0f1740 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -245,6 +245,7 @@ struct swap_info_struct {
 #ifdef CONFIG_XSWAP
 	struct vm_struct	*cluster_vm;	/* VM_SPARSE area for cluster_info */
 	unsigned long		nr_clusters_max;/* total clusters in the xswap address space */
+	unsigned long		nr_clusters;	/* how far the array may grow */
 	unsigned long		nr_clusters_mapped; /* currently mapped cluster count */
 	struct work_struct	xswap_shrink_work; /* deferred shrink trigger */
 	struct mutex		xswap_lock;	/* serialize map/unmap operations */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index cac084bc72d6..2cf6ba0bd0c0 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1319,16 +1319,18 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si,
 
 #ifdef CONFIG_XSWAP
 	/* For xswap: grow the cluster_info array, then retry. */
-	if (!found && (si->flags & SWP_XSWAP) &&
-	    READ_ONCE(si->nr_clusters_mapped) < READ_ONCE(si->nr_clusters_max) &&
-	    list_empty(&si->free_clusters)) {
-		unsigned long nr_new = min(READ_ONCE(si->nr_clusters_max) -
-					  READ_ONCE(si->nr_clusters_mapped),
-					  XSWAP_GROW_CLUSTERS);
-		unsigned long start = READ_ONCE(si->nr_clusters_mapped);
-		unsigned long i;
+	if (!found && (si->flags & SWP_XSWAP) && list_empty(&si->free_clusters)) {
+		unsigned long ceiling = READ_ONCE(si->nr_clusters);
+		unsigned long mapped = READ_ONCE(si->nr_clusters_mapped);
+		unsigned long nr_new, start, i;
 		int ret;
 
+		if (mapped >= ceiling)
+			goto done;
+
+		nr_new = min(ceiling - mapped, XSWAP_GROW_CLUSTERS);
+		start = mapped;
+
 		/*
 		 * Mapping pages can sleep.  The lock only guards the per-cpu
 		 * cluster cache, which this path does not touch.
@@ -4294,6 +4296,7 @@ static int setup_swap_clusters_info(struct swap_info_struct *si,
 		cluster_info = vm->addr;
 		si->cluster_vm = vm;
 		si->nr_clusters_max = nr_clusters;
+		si->nr_clusters = nr_clusters;
 		si->cluster_info = cluster_info;
 
 		/* Must be initialized before xswap_map_clusters() locks it. */
-- 
2.54.0