[PATCH v2] mm/slub: Simplify get_partial_node()

[sxwjean]

From: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>

Remove the check of !kmem_cache_has_cpu_partial() because it is always
false, we've known this by calling kmem_cache_debug() before calling
remove_partial(), so we can remove the check.

Meanwhile, redo filling cpu partial and add comment to improve the
readability.

Signed-off-by: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
---
Changes in v2:
 - Use "#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)" to instead 
   "if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))" to fix build error.
   (Thanks Chengming Zhou)
 - Add __maybe_unused for partial_slabs to prevent compiler warning.

v1: 
 https://lore.kernel.org/linux-kernel/20240311132720.37741-1-sxwjean@xxxxxx/T/
---
 mm/slub.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index a3ab096c38c0..ab526960ee5b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2588,7 +2588,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
 {
 	struct slab *slab, *slab2, *partial = NULL;
 	unsigned long flags;
-	unsigned int partial_slabs = 0;
+	unsigned int __maybe_unused partial_slabs = 0;
 
 	/*
 	 * Racy check. If we mistakenly see no partial slabs then we
@@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
 		if (!partial) {
 			partial = slab;
 			stat(s, ALLOC_FROM_PARTIAL);
-		} else {
-			put_cpu_partial(s, slab, 0);
-			stat(s, CPU_PARTIAL_NODE);
-			partial_slabs++;
+
+			/* Fill cpu partial if needed from next iteration, or break */
+			if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
+				continue;
+			else
+				break;
 		}
-#ifdef CONFIG_SLUB_CPU_PARTIAL
-		if (!kmem_cache_has_cpu_partial(s)
-			|| partial_slabs > s->cpu_partial_slabs / 2)
+
+#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)
+		put_cpu_partial(s, slab, 0);
+		stat(s, CPU_PARTIAL_NODE);
+
+		if (++partial_slabs > s->cpu_partial_slabs/2)
 			break;
-#else
-		break;
 #endif
-
 	}
 	spin_unlock_irqrestore(&n->list_lock, flags);
 	return partial;
-- 
2.34.1