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slub: Make PREEMPT_RT support less convoluted 

The slub code already has a few helpers depending on PREEMPT_RT. Add a few
more and get rid of the CONFIG_PREEMPT_RT conditionals all over the place.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Thomas Gleixner 2022-08-25 09:51:36 +02:00 committed by Vlastimil Babka
parent 5875e59828
commit 1f04b07d97
1 changed files with 24 additions and 32 deletions
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56
mm/slub.c
View File

@ -104,9 +104,11 @@
* except the stat counters. This is a percpu structure manipulated only by
* the local cpu, so the lock protects against being preempted or interrupted
* by an irq. Fast path operations rely on lockless operations instead.
* On PREEMPT_RT, the local lock does not actually disable irqs (and thus
* prevent the lockless operations), so fastpath operations also need to take
* the lock and are no longer lockless.
*
* On PREEMPT_RT, the local lock neither disables interrupts nor preemption
* which means the lockless fastpath cannot be used as it might interfere with
* an in-progress slow path operations. In this case the local lock is always
* taken but it still utilizes the freelist for the common operations.
*
* lockless fastpaths
*
@ -167,8 +169,9 @@
* 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)
#define slub_get_cpu_ptr(var) get_cpu_ptr(var)
#define slub_put_cpu_ptr(var) put_cpu_ptr(var)
#define USE_LOCKLESS_FAST_PATH() (true)
#else
#define slub_get_cpu_ptr(var) \
({ \
@ -180,6 +183,7 @@ do { \
(void)(var); \
migrate_enable(); \
} while (0)
#define USE_LOCKLESS_FAST_PATH() (false)
#endif
#ifdef CONFIG_SLUB_DEBUG
@ -474,7 +478,7 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab
void *freelist_new, unsigned long counters_new,
const char *n)
{
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
if (USE_LOCKLESS_FAST_PATH())
lockdep_assert_irqs_disabled();
#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
@ -3288,14 +3292,8 @@ redo:
object = c->freelist;
slab = c->slab;
/*
* We cannot use the lockless fastpath on PREEMPT_RT because if a
* slowpath has taken the local_lock_irqsave(), it is not protected
* against a fast path operation in an irq handler. So we need to take
* the slow path which uses local_lock. It is still relatively fast if
* there is a suitable cpu freelist.
*/
if (IS_ENABLED(CONFIG_PREEMPT_RT) ||
if (!USE_LOCKLESS_FAST_PATH() ||
unlikely(!object || !slab || !node_match(slab, node))) {
object = __slab_alloc(s, gfpflags, node, addr, c);
} else {
@ -3555,6 +3553,7 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
void *tail_obj = tail ? : head;
struct kmem_cache_cpu *c;
unsigned long tid;
void **freelist;
redo:
/*
@ -3569,9 +3568,13 @@ redo:
/* Same with comment on barrier() in slab_alloc_node() */
barrier();
if (likely(slab == c->slab)) {
#ifndef CONFIG_PREEMPT_RT
void **freelist = READ_ONCE(c->freelist);
if (unlikely(slab != c->slab)) {
__slab_free(s, slab, head, tail_obj, cnt, addr);
return;
}
if (USE_LOCKLESS_FAST_PATH()) {
freelist = READ_ONCE(c->freelist);
set_freepointer(s, tail_obj, freelist);
@ -3583,16 +3586,8 @@ redo:
note_cmpxchg_failure("slab_free", s, tid);
goto redo;
}
#else /* CONFIG_PREEMPT_RT */
/*
* We cannot use the lockless fastpath on PREEMPT_RT because if
* a slowpath has taken the local_lock_irqsave(), it is not
* protected against a fast path operation in an irq handler. So
* we need to take the local_lock. We shouldn't simply defer to
* __slab_free() as that wouldn't use the cpu freelist at all.
*/
void **freelist;
} else {
/* Update the free list under the local lock */
local_lock(&s->cpu_slab->lock);
c = this_cpu_ptr(s->cpu_slab);
if (unlikely(slab != c->slab)) {
@ -3607,11 +3602,8 @@ redo:
c->tid = next_tid(tid);
local_unlock(&s->cpu_slab->lock);
#endif
stat(s, FREE_FASTPATH);
} else
__slab_free(s, slab, head, tail_obj, cnt, addr);
}
stat(s, FREE_FASTPATH);
}
static __always_inline void slab_free(struct kmem_cache *s, struct slab *slab,