linux-kernel - [PATCH v3 1/2] mm/slub: limit number of node partial slabs only in cache creation

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Date:   Mon,  7 Mar 2022 07:40:55 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     linux-mm@...ck.org
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Marco Elver <elver@...gle.com>,
        Matthew WilCox <willy@...radead.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        linux-kernel@...r.kernel.org, 42.hyeyoo@...il.com
Subject: [PATCH v3 1/2] mm/slub: limit number of node partial slabs 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 limits value of
min_partial 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.

[ rientjes@...gle.com: Fold set_min_partial() into its callers ]

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 261474092e43..1ce09b0347ad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4000,15 +4000,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
 	return 1;
 }
 
-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;
-}
-
 static void set_cpu_partial(struct kmem_cache *s)
 {
 #ifdef CONFIG_SLUB_CPU_PARTIAL
@@ -4215,7 +4206,8 @@ 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);
+	s->min_partial = min_t(unsigned long, MAX_PARTIAL, ilog2(s->size) / 2);
+	s->min_partial = max_t(unsigned long, MIN_PARTIAL, s->min_partial);
 
 	set_cpu_partial(s);
 
@@ -5396,7 +5388,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
 	if (err)
 		return err;
 
-	set_min_partial(s, min);
+	s->min_partial = min;
 	return length;
 }
 SLAB_ATTR(min_partial);
-- 
2.33.1