[PATCH 2/2] mm, swap: merge common convention and simplify allocation helper

[Kairui Song]

From: Kairui Song <kasong@xxxxxxxxxxx>

almost all callers of the cluster scan helper require the: lock -> check
usefulness/emptiness -> unlock routine. So merge them into the same
helper to simplify the code.

This should also improve the scan slightly, as a few callers didn't
check the emptiness, which might help reduce fragmentation in rare
cases.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/swapfile.c | 30 ++++++++----------------------
 1 file changed, 8 insertions(+), 22 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index bcac10d96fb5..03cc0ff4dc8c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -923,11 +923,14 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
 	bool need_reclaim, ret, usable;
 
 	lockdep_assert_held(&ci->lock);
-	VM_WARN_ON(!cluster_is_usable(ci, order));
 
-	if (end < nr_pages || ci->count + nr_pages > SWAPFILE_CLUSTER)
+	if (!cluster_is_usable(ci, order) || end < nr_pages ||
+	    ci->count + nr_pages > SWAPFILE_CLUSTER)
 		goto out;
 
+	if (cluster_is_empty(ci))
+		offset = cluster_offset(si, ci);
+
 	for (end -= nr_pages; offset <= end; offset += nr_pages) {
 		need_reclaim = false;
 		if (!cluster_scan_range(si, ci, offset, nr_pages, &need_reclaim))
@@ -1060,14 +1063,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si,
 			goto new_cluster;
 
 		ci = swap_cluster_lock(si, offset);
-		/* Cluster could have been used by another order */
-		if (cluster_is_usable(ci, order)) {
-			if (cluster_is_empty(ci))
-				offset = cluster_offset(si, ci);
-			found = alloc_swap_scan_cluster(si, ci, folio, offset);
-		} else {
-			swap_cluster_unlock(ci);
-		}
+		found = alloc_swap_scan_cluster(si, ci, folio, offset);
 		if (found)
 			goto done;
 	}
@@ -1332,14 +1328,7 @@ static bool swap_alloc_fast(struct folio *folio)
 		return false;
 
 	ci = swap_cluster_lock(si, offset);
-	if (cluster_is_usable(ci, order)) {
-		if (cluster_is_empty(ci))
-			offset = cluster_offset(si, ci);
-		alloc_swap_scan_cluster(si, ci, folio, offset);
-	} else {
-		swap_cluster_unlock(ci);
-	}
-
+	alloc_swap_scan_cluster(si, ci, folio, offset);
 	put_swap_device(si);
 	return folio_test_swapcache(folio);
 }
@@ -1945,10 +1934,7 @@ swp_entry_t swap_alloc_hibernation_slot(int type)
 		pcp_offset = this_cpu_read(percpu_swap_cluster.offset[0]);
 		if (pcp_si == si && pcp_offset) {
 			ci = swap_cluster_lock(si, pcp_offset);
-			if (cluster_is_usable(ci, 0))
-				offset = alloc_swap_scan_cluster(si, ci, NULL, pcp_offset);
-			else
-				swap_cluster_unlock(ci);
+			offset = alloc_swap_scan_cluster(si, ci, NULL, pcp_offset);
 		}
 		if (!offset)
 			offset = cluster_alloc_swap_entry(si, NULL);

-- 
2.52.0