linux-kernel - [PATCH RFC 05/19] slab: add sheaves to most caches

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20251023-sheaves-for-all-v1-5-6ffa2c9941c0@suse.cz>
Date: Thu, 23 Oct 2025 15:52:27 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>
Cc: 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 05/19] slab: add sheaves to most caches

In the first step to replace cpu (partial) slabs with sheaves, enable
sheaves for almost all caches. Treat args->sheaf_capacity as a minimum,
and calculate sheaf capacity with a formula that roughly follows the
formula for number of objects in cpu partial slabs in set_cpu_partial().

This should achieve roughly similar contention on the barn spin lock as
there's currently for node list_lock without sheaves, to make
benchmarking results comparable. It can be further tuned later.

Don't enable sheaves for kmalloc caches yet, as that needs further
changes to bootstraping.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 include/linux/slab.h |  6 ------
 mm/slub.c            | 51 +++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index cf443f064a66..e42aa6a3d202 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -57,9 +57,7 @@ enum _slab_flag_bits {
 #endif
 	_SLAB_OBJECT_POISON,
 	_SLAB_CMPXCHG_DOUBLE,
-#ifdef CONFIG_SLAB_OBJ_EXT
 	_SLAB_NO_OBJ_EXT,
-#endif
 	_SLAB_FLAGS_LAST_BIT
 };
 
@@ -238,11 +236,7 @@ enum _slab_flag_bits {
 #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
 
 /* Slab created using create_boot_cache */
-#ifdef CONFIG_SLAB_OBJ_EXT
 #define SLAB_NO_OBJ_EXT		__SLAB_FLAG_BIT(_SLAB_NO_OBJ_EXT)
-#else
-#define SLAB_NO_OBJ_EXT		__SLAB_FLAG_UNUSED
-#endif
 
 /*
  * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
diff --git a/mm/slub.c b/mm/slub.c
index f2b2a6180759..a6e58d3708f4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -7810,6 +7810,48 @@ static void set_cpu_partial(struct kmem_cache *s)
 #endif
 }
 
+static unsigned int calculate_sheaf_capacity(struct kmem_cache *s,
+					     struct kmem_cache_args *args)
+
+{
+	unsigned int capacity;
+	size_t size;
+
+
+	if (IS_ENABLED(CONFIG_SLUB_TINY) || s->flags & SLAB_DEBUG_FLAGS)
+		return 0;
+
+	/* bootstrap caches can't have sheaves for now */
+	if (s->flags & SLAB_NO_OBJ_EXT)
+		return 0;
+
+	/*
+	 * For now we use roughly similar formula (divided by two as there are
+	 * two percpu sheaves) as what was used for percpu partial slabs, which
+	 * should result in similar lock contention (barn or list_lock)
+	 */
+	if (s->size >= PAGE_SIZE)
+		capacity = 4;
+	else if (s->size >= 1024)
+		capacity = 12;
+	else if (s->size >= 256)
+		capacity = 26;
+	else
+		capacity = 60;
+
+	/* Increment capacity to make sheaf exactly a kmalloc size bucket */
+	size = struct_size_t(struct slab_sheaf, objects, capacity);
+	size = kmalloc_size_roundup(size);
+	capacity = (size - struct_size_t(struct slab_sheaf, objects, 0)) / sizeof(void *);
+
+	/*
+	 * Respect an explicit request for capacity that's typically motivated by
+	 * expected maximum size of kmem_cache_prefill_sheaf() to not end up
+	 * using low-performance oversize sheaves
+	 */
+	return max(capacity, args->sheaf_capacity);
+}
+
 /*
  * calculate_sizes() determines the order and the distribution of data within
  * a slab object.
@@ -7944,6 +7986,10 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 	if (s->flags & SLAB_RECLAIM_ACCOUNT)
 		s->allocflags |= __GFP_RECLAIMABLE;
 
+	/* kmalloc caches need extra care to support sheaves */
+	if (!is_kmalloc_cache(s))
+		s->sheaf_capacity = calculate_sheaf_capacity(s, args);
+
 	/*
 	 * Determine the number of objects per slab
 	 */
@@ -8562,15 +8608,12 @@ int do_kmem_cache_create(struct kmem_cache *s, const char *name,
 
 	set_cpu_partial(s);
 
-	if (args->sheaf_capacity && !IS_ENABLED(CONFIG_SLUB_TINY)
-					&& !(s->flags & SLAB_DEBUG_FLAGS)) {
+	if (s->sheaf_capacity) {
 		s->cpu_sheaves = alloc_percpu(struct slub_percpu_sheaves);
 		if (!s->cpu_sheaves) {
 			err = -ENOMEM;
 			goto out;
 		}
-		// TODO: increase capacity to grow slab_sheaf up to next kmalloc size?
-		s->sheaf_capacity = args->sheaf_capacity;
 	}
 
 #ifdef CONFIG_NUMA

-- 
2.51.1