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Message-Id: <20260116-sheaves-for-all-v3-7-5595cb000772@suse.cz>
Date: Fri, 16 Jan 2026 15:40:27 +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 v3 07/21] slab: make percpu sheaves compatible with
kmalloc_nolock()/kfree_nolock()
Before we enable percpu sheaves for kmalloc caches, we need to make sure
kmalloc_nolock() and kfree_nolock() will continue working properly and
not spin when not allowed to.
Percpu sheaves themselves use local_trylock() so they are already
compatible. We just need to be careful with the barn->lock spin_lock.
Pass a new allow_spin parameter where necessary to use
spin_trylock_irqsave().
In kmalloc_nolock_noprof() we can now attempt alloc_from_pcs() safely,
for now it will always fail until we enable sheaves for kmalloc caches
next. Similarly in kfree_nolock() we can attempt free_to_pcs().
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/slub.c | 79 ++++++++++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 56 insertions(+), 23 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 706cb6398f05..b385247c219f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2893,7 +2893,8 @@ static void pcs_destroy(struct kmem_cache *s)
s->cpu_sheaves = NULL;
}
-static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn)
+static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn,
+ bool allow_spin)
{
struct slab_sheaf *empty = NULL;
unsigned long flags;
@@ -2901,7 +2902,10 @@ static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn)
if (!data_race(barn->nr_empty))
return NULL;
- spin_lock_irqsave(&barn->lock, flags);
+ if (likely(allow_spin))
+ spin_lock_irqsave(&barn->lock, flags);
+ else if (!spin_trylock_irqsave(&barn->lock, flags))
+ return NULL;
if (likely(barn->nr_empty)) {
empty = list_first_entry(&barn->sheaves_empty,
@@ -2978,7 +2982,8 @@ static struct slab_sheaf *barn_get_full_or_empty_sheaf(struct node_barn *barn)
* change.
*/
static struct slab_sheaf *
-barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
+barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty,
+ bool allow_spin)
{
struct slab_sheaf *full = NULL;
unsigned long flags;
@@ -2986,7 +2991,10 @@ barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
if (!data_race(barn->nr_full))
return NULL;
- spin_lock_irqsave(&barn->lock, flags);
+ if (likely(allow_spin))
+ spin_lock_irqsave(&barn->lock, flags);
+ else if (!spin_trylock_irqsave(&barn->lock, flags))
+ return NULL;
if (likely(barn->nr_full)) {
full = list_first_entry(&barn->sheaves_full, struct slab_sheaf,
@@ -3007,7 +3015,8 @@ barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
* barn. But if there are too many full sheaves, reject this with -E2BIG.
*/
static struct slab_sheaf *
-barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full)
+barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full,
+ bool allow_spin)
{
struct slab_sheaf *empty;
unsigned long flags;
@@ -3018,7 +3027,10 @@ barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full)
if (!data_race(barn->nr_empty))
return ERR_PTR(-ENOMEM);
- spin_lock_irqsave(&barn->lock, flags);
+ if (likely(allow_spin))
+ spin_lock_irqsave(&barn->lock, flags);
+ else if (!spin_trylock_irqsave(&barn->lock, flags))
+ return ERR_PTR(-EBUSY);
if (likely(barn->nr_empty)) {
empty = list_first_entry(&barn->sheaves_empty, struct slab_sheaf,
@@ -5012,7 +5024,8 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
return NULL;
}
- full = barn_replace_empty_sheaf(barn, pcs->main);
+ full = barn_replace_empty_sheaf(barn, pcs->main,
+ gfpflags_allow_spinning(gfp));
if (full) {
stat(s, BARN_GET);
@@ -5029,7 +5042,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
empty = pcs->spare;
pcs->spare = NULL;
} else {
- empty = barn_get_empty_sheaf(barn);
+ empty = barn_get_empty_sheaf(barn, true);
}
}
@@ -5169,7 +5182,8 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node)
}
static __fastpath_inline
-unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
+unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, gfp_t gfp, size_t size,
+ void **p)
{
struct slub_percpu_sheaves *pcs;
struct slab_sheaf *main;
@@ -5203,7 +5217,8 @@ unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
return allocated;
}
- full = barn_replace_empty_sheaf(barn, pcs->main);
+ full = barn_replace_empty_sheaf(barn, pcs->main,
+ gfpflags_allow_spinning(gfp));
if (full) {
stat(s, BARN_GET);
@@ -5701,7 +5716,7 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
gfp_t alloc_gfp = __GFP_NOWARN | __GFP_NOMEMALLOC | gfp_flags;
struct kmem_cache *s;
bool can_retry = true;
- void *ret = ERR_PTR(-EBUSY);
+ void *ret;
VM_WARN_ON_ONCE(gfp_flags & ~(__GFP_ACCOUNT | __GFP_ZERO |
__GFP_NO_OBJ_EXT));
@@ -5732,6 +5747,12 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
*/
return NULL;
+ ret = alloc_from_pcs(s, alloc_gfp, node);
+ if (ret)
+ goto success;
+
+ ret = ERR_PTR(-EBUSY);
+
/*
* Do not call slab_alloc_node(), since trylock mode isn't
* compatible with slab_pre_alloc_hook/should_failslab and
@@ -5768,6 +5789,7 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
ret = NULL;
}
+success:
maybe_wipe_obj_freeptr(s, ret);
slab_post_alloc_hook(s, NULL, alloc_gfp, 1, &ret,
slab_want_init_on_alloc(alloc_gfp, s), size);
@@ -6088,7 +6110,8 @@ static void __pcs_install_empty_sheaf(struct kmem_cache *s,
* unlocked.
*/
static struct slub_percpu_sheaves *
-__pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
+__pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
+ bool allow_spin)
{
struct slab_sheaf *empty;
struct node_barn *barn;
@@ -6112,7 +6135,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
put_fail = false;
if (!pcs->spare) {
- empty = barn_get_empty_sheaf(barn);
+ empty = barn_get_empty_sheaf(barn, allow_spin);
if (empty) {
pcs->spare = pcs->main;
pcs->main = empty;
@@ -6126,7 +6149,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
return pcs;
}
- empty = barn_replace_full_sheaf(barn, pcs->main);
+ empty = barn_replace_full_sheaf(barn, pcs->main, allow_spin);
if (!IS_ERR(empty)) {
stat(s, BARN_PUT);
@@ -6134,7 +6157,8 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
return pcs;
}
- if (PTR_ERR(empty) == -E2BIG) {
+ /* sheaf_flush_unused() doesn't support !allow_spin */
+ if (PTR_ERR(empty) == -E2BIG && allow_spin) {
/* Since we got here, spare exists and is full */
struct slab_sheaf *to_flush = pcs->spare;
@@ -6159,6 +6183,14 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
alloc_empty:
local_unlock(&s->cpu_sheaves->lock);
+ /*
+ * alloc_empty_sheaf() doesn't support !allow_spin and it's
+ * easier to fall back to freeing directly without sheaves
+ * than add the support (and to sheaf_flush_unused() above)
+ */
+ if (!allow_spin)
+ return NULL;
+
empty = alloc_empty_sheaf(s, GFP_NOWAIT);
if (empty)
goto got_empty;
@@ -6201,7 +6233,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
* The object is expected to have passed slab_free_hook() already.
*/
static __fastpath_inline
-bool free_to_pcs(struct kmem_cache *s, void *object)
+bool free_to_pcs(struct kmem_cache *s, void *object, bool allow_spin)
{
struct slub_percpu_sheaves *pcs;
@@ -6212,7 +6244,7 @@ bool free_to_pcs(struct kmem_cache *s, void *object)
if (unlikely(pcs->main->size == s->sheaf_capacity)) {
- pcs = __pcs_replace_full_main(s, pcs);
+ pcs = __pcs_replace_full_main(s, pcs, allow_spin);
if (unlikely(!pcs))
return false;
}
@@ -6319,7 +6351,7 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)
goto fail;
}
- empty = barn_get_empty_sheaf(barn);
+ empty = barn_get_empty_sheaf(barn, true);
if (empty) {
pcs->rcu_free = empty;
@@ -6437,7 +6469,7 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
goto no_empty;
if (!pcs->spare) {
- empty = barn_get_empty_sheaf(barn);
+ empty = barn_get_empty_sheaf(barn, true);
if (!empty)
goto no_empty;
@@ -6451,7 +6483,7 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
goto do_free;
}
- empty = barn_replace_full_sheaf(barn, pcs->main);
+ empty = barn_replace_full_sheaf(barn, pcs->main, true);
if (IS_ERR(empty)) {
stat(s, BARN_PUT_FAIL);
goto no_empty;
@@ -6703,7 +6735,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())
&& likely(!slab_test_pfmemalloc(slab))) {
- if (likely(free_to_pcs(s, object)))
+ if (likely(free_to_pcs(s, object, true)))
return;
}
@@ -6964,7 +6996,8 @@ void kfree_nolock(const void *object)
* since kasan quarantine takes locks and not supported from NMI.
*/
kasan_slab_free(s, x, false, false, /* skip quarantine */true);
- do_slab_free(s, slab, x, x, 0, _RET_IP_);
+ if (!free_to_pcs(s, x, false))
+ do_slab_free(s, slab, x, x, 0, _RET_IP_);
}
EXPORT_SYMBOL_GPL(kfree_nolock);
@@ -7516,7 +7549,7 @@ int kmem_cache_alloc_bulk_noprof(struct kmem_cache *s, gfp_t flags, size_t size,
size--;
}
- i = alloc_from_pcs_bulk(s, size, p);
+ i = alloc_from_pcs_bulk(s, flags, size, p);
if (i < size) {
/*
--
2.52.0
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