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authorVlastimil Babka <vbabka@suse.cz>2021-05-21 14:03:23 +0200
committerVlastimil Babka <vbabka@suse.cz>2021-09-04 10:21:32 +0200
commit25c00c506e8176d03f9ad821cc349230dfb5dc1a (patch)
tree4942ab6bec74b8736658937c427378c65563c89d /mm/slub.c
parente0a043aa4145a14d6a8864847811491699a81310 (diff)
mm, slub: use migrate_disable() on PREEMPT_RT
We currently use preempt_disable() (directly or via get_cpu_ptr()) to stabilize the pointer to kmem_cache_cpu. On PREEMPT_RT this would be incompatible with the list_lock spinlock. We can use migrate_disable() instead, but that increases overhead on !PREEMPT_RT as it's an unconditional function call. In order to get the best available mechanism on both PREEMPT_RT and !PREEMPT_RT, introduce private slub_get_cpu_ptr() and slub_put_cpu_ptr() wrappers and use them. Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Diffstat (limited to 'mm/slub.c')
-rw-r--r--mm/slub.c39
1 files changed, 30 insertions, 9 deletions
diff --git a/mm/slub.c b/mm/slub.c
index f4b33d2fddc1..38d4cc51e880 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -118,6 +118,26 @@
* the fast path and disables lockless freelists.
*/
+/*
+ * We could simply use migrate_disable()/enable() but as long as it's a
+ * function call even on !PREEMPT_RT, use inline preempt_disable() there.
+ */
+#ifndef CONFIG_PREEMPT_RT
+#define slub_get_cpu_ptr(var) get_cpu_ptr(var)
+#define slub_put_cpu_ptr(var) put_cpu_ptr(var)
+#else
+#define slub_get_cpu_ptr(var) \
+({ \
+ migrate_disable(); \
+ this_cpu_ptr(var); \
+})
+#define slub_put_cpu_ptr(var) \
+do { \
+ (void)(var); \
+ migrate_enable(); \
+} while (0)
+#endif
+
#ifdef CONFIG_SLUB_DEBUG
#ifdef CONFIG_SLUB_DEBUG_ON
DEFINE_STATIC_KEY_TRUE(slub_debug_enabled);
@@ -2852,7 +2872,7 @@ redo:
if (unlikely(!pfmemalloc_match_unsafe(page, gfpflags)))
goto deactivate_slab;
- /* must check again c->page in case IRQ handler changed it */
+ /* must check again c->page in case we got preempted and it changed */
local_irq_save(flags);
if (unlikely(page != c->page)) {
local_irq_restore(flags);
@@ -2911,7 +2931,8 @@ new_slab:
}
if (unlikely(!slub_percpu_partial(c))) {
local_irq_restore(flags);
- goto new_objects; /* stolen by an IRQ handler */
+ /* we were preempted and partial list got empty */
+ goto new_objects;
}
page = c->page = slub_percpu_partial(c);
@@ -2927,9 +2948,9 @@ new_objects:
if (freelist)
goto check_new_page;
- put_cpu_ptr(s->cpu_slab);
+ slub_put_cpu_ptr(s->cpu_slab);
page = new_slab(s, gfpflags, node);
- c = get_cpu_ptr(s->cpu_slab);
+ c = slub_get_cpu_ptr(s->cpu_slab);
if (unlikely(!page)) {
slab_out_of_memory(s, gfpflags, node);
@@ -3012,12 +3033,12 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
* cpu before disabling preemption. Need to reload cpu area
* pointer.
*/
- c = get_cpu_ptr(s->cpu_slab);
+ c = slub_get_cpu_ptr(s->cpu_slab);
#endif
p = ___slab_alloc(s, gfpflags, node, addr, c);
#ifdef CONFIG_PREEMPT_COUNT
- put_cpu_ptr(s->cpu_slab);
+ slub_put_cpu_ptr(s->cpu_slab);
#endif
return p;
}
@@ -3546,7 +3567,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
* IRQs, which protects against PREEMPT and interrupts
* handlers invoking normal fastpath.
*/
- c = get_cpu_ptr(s->cpu_slab);
+ c = slub_get_cpu_ptr(s->cpu_slab);
local_irq_disable();
for (i = 0; i < size; i++) {
@@ -3592,7 +3613,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
}
c->tid = next_tid(c->tid);
local_irq_enable();
- put_cpu_ptr(s->cpu_slab);
+ slub_put_cpu_ptr(s->cpu_slab);
/*
* memcg and kmem_cache debug support and memory initialization.
@@ -3602,7 +3623,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
slab_want_init_on_alloc(flags, s));
return i;
error:
- put_cpu_ptr(s->cpu_slab);
+ slub_put_cpu_ptr(s->cpu_slab);
slab_post_alloc_hook(s, objcg, flags, i, p, false);
__kmem_cache_free_bulk(s, i, p);
return 0;