linux-kernel - [PATCH RFC v2 03/20] mm/slab: make caches with sheaves mergeable

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Message-Id: <20260112-sheaves-for-all-v2-3-98225cfb50cf@suse.cz>
Date: Mon, 12 Jan 2026 16:16:57 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Harry Yoo <harry.yoo@...cle.com>, Petr Tesarik <ptesarik@...e.com>, 
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Hao Li <hao.li@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
 Uladzislau Rezki <urezki@...il.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Suren Baghdasaryan <surenb@...gle.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
 bpf@...r.kernel.org, kasan-dev@...glegroups.com, 
 Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH RFC v2 03/20] mm/slab: make caches with sheaves mergeable

Before enabling sheaves for all caches (with automatically determined
capacity), their enablement should no longer prevent merging of caches.
Limit this merge prevention only to caches that were created with a
specific sheaf capacity, by adding the SLAB_NO_MERGE flag to them.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slab_common.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 52591d9c04f3..54c17dc6d5ec 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -163,9 +163,6 @@ int slab_unmergeable(struct kmem_cache *s)
 		return 1;
 #endif

-	if (s->cpu_sheaves)
-		return 1;
-
 	/*
 	 * We may have set a slab to be unmergeable during bootstrap.
 	 */
@@ -190,9 +187,6 @@ static struct kmem_cache *find_mergeable(unsigned int size, slab_flags_t flags,
 	if (IS_ENABLED(CONFIG_HARDENED_USERCOPY) && args->usersize)
 		return NULL;

-	if (args->sheaf_capacity)
-		return NULL;
-
 	flags = kmem_cache_flags(flags, name);

 	if (flags & SLAB_NEVER_MERGE)
@@ -337,6 +331,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 	flags &= ~SLAB_DEBUG_FLAGS;
 #endif

+	/*
+	 * Caches with specific capacity are special enough. It's simpler to
+	 * make them unmergeable.
+	 */
+	if (args->sheaf_capacity)
+		flags |= SLAB_NO_MERGE;
+
 	mutex_lock(&slab_mutex);

 	err = kmem_cache_sanity_check(name, object_size);

-- 
2.52.0