linux-kernel - [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

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Date:   Mon, 21 Feb 2022 10:53:35 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     linux-mm@...ck.org
Cc:     Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

SLUB sets number of minimum partial slabs for node (min_partial) using
set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
to avoid excessive use of page allocator.

set_min_partial() limits value of min_partial between MIN_PARTIAL and
MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
too, Only limit value of min_partial in kmem_cache_open() so that it
can be changed to value that a user wants.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
---
 mm/slub.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 3a4458976ab7..a4964deccb61 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4002,10 +4002,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
 
 static void set_min_partial(struct kmem_cache *s, unsigned long min)
 {
-	if (min < MIN_PARTIAL)
-		min = MIN_PARTIAL;
-	else if (min > MAX_PARTIAL)
-		min = MAX_PARTIAL;
 	s->min_partial = min;
 }
 
@@ -4184,6 +4180,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 
 static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 {
+	int min_partial;
+
 	s->flags = kmem_cache_flags(s->size, flags, s->name);
 #ifdef CONFIG_SLAB_FREELIST_HARDENED
 	s->random = get_random_long();
@@ -4215,7 +4213,10 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 	 * The larger the object size is, the more slabs we want on the partial
 	 * list to avoid pounding the page allocator excessively.
 	 */
-	set_min_partial(s, ilog2(s->size) / 2);
+	min_partial = min(MAX_PARTIAL, ilog2(s->size) / 2);
+	min_partial = max(MIN_PARTIAL, min_partial);
+
+	set_min_partial(s, min_partial);
 
 	set_cpu_partial(s);
 
-- 
2.33.1