Commit 1759415e authored by Christoph Lameter's avatar Christoph Lameter Committed by Pekka Enberg
Browse files

slub: Remove CONFIG_CMPXCHG_LOCAL ifdeffery 



Remove the #ifdefs. This means that the irqsafe_cpu_cmpxchg_double() is used
everywhere.

There may be performance implications since:

A. We now have to manage a transaction ID for all arches

B. The interrupt holdoff for arches not supporting CONFIG_CMPXCHG_LOCAL is reduced
to a very short irqoff section.

There are no multiple irqoff/irqon sequences as a result of this change. Even in the fallback
case we only have to do one disable and enable like before.

Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
Signed-off-by: default avatarPekka Enberg <penberg@kernel.org>
parent 8dc16c6c

include/linux/slub_def.h

+0 −2
Original line number Diff line number Diff line
@@ -37,9 +37,7 @@ enum stat_item { 


struct kmem_cache_cpu {

	void **freelist;	/* Pointer to next available object */

#ifdef CONFIG_CMPXCHG_LOCAL

	unsigned long tid;	/* Globally unique transaction id */

#endif

	struct page *page;	/* The slab from which we are allocating */

	int node;		/* The node of the page (or -1 for debug) */

#ifdef CONFIG_SLUB_STATS

mm/slub.c

+0 −56
Original line number Diff line number Diff line
@@ -1551,7 +1551,6 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail) 
	}

}



#ifdef CONFIG_CMPXCHG_LOCAL

#ifdef CONFIG_PREEMPT

/*

 * Calculate the next globally unique transaction for disambiguiation
@@ -1611,17 +1610,12 @@ static inline void note_cmpxchg_failure(const char *n, 
	stat(s, CMPXCHG_DOUBLE_CPU_FAIL);

}



#endif



void init_kmem_cache_cpus(struct kmem_cache *s)

{

#ifdef CONFIG_CMPXCHG_LOCAL

	int cpu;



	for_each_possible_cpu(cpu)

		per_cpu_ptr(s->cpu_slab, cpu)->tid = init_tid(cpu);

#endif



}

/*

 * Remove the cpu slab
@@ -1654,9 +1648,7 @@ static void deactivate_slab(struct kmem_cache *s, struct kmem_cache_cpu *c) 
		page->inuse--;

	}

	c->page = NULL;

#ifdef CONFIG_CMPXCHG_LOCAL

	c->tid = next_tid(c->tid);

#endif

	unfreeze_slab(s, page, tail);

}
@@ -1791,7 +1783,6 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, 
{

	void **object;

	struct page *page;

#ifdef CONFIG_CMPXCHG_LOCAL

	unsigned long flags;



	local_irq_save(flags);
@@ -1802,7 +1793,6 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, 
	 * pointer.

	 */

	c = this_cpu_ptr(s->cpu_slab);

#endif

#endif



	/* We handle __GFP_ZERO in the caller */
@@ -1831,10 +1821,8 @@ load_freelist: 


unlock_out:

	slab_unlock(page);

#ifdef CONFIG_CMPXCHG_LOCAL

	c->tid = next_tid(c->tid);

	local_irq_restore(flags);

#endif

	stat(s, ALLOC_SLOWPATH);

	return object;
@@ -1873,9 +1861,7 @@ load_from_page: 
	}

	if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())

		slab_out_of_memory(s, gfpflags, node);

#ifdef CONFIG_CMPXCHG_LOCAL

	local_irq_restore(flags);

#endif

	return NULL;

debug:

	if (!alloc_debug_processing(s, page, object, addr))
@@ -1902,20 +1888,12 @@ static __always_inline void *slab_alloc(struct kmem_cache *s, 
{

	void **object;

	struct kmem_cache_cpu *c;

#ifdef CONFIG_CMPXCHG_LOCAL

	unsigned long tid;

#else

	unsigned long flags;

#endif



	if (slab_pre_alloc_hook(s, gfpflags))

		return NULL;



#ifndef CONFIG_CMPXCHG_LOCAL

	local_irq_save(flags);

#else

redo:

#endif



	/*

	 * Must read kmem_cache cpu data via this cpu ptr. Preemption is
@@ -1925,7 +1903,6 @@ redo: 
	 */

	c = __this_cpu_ptr(s->cpu_slab);



#ifdef CONFIG_CMPXCHG_LOCAL

	/*

	 * The transaction ids are globally unique per cpu and per operation on

	 * a per cpu queue. Thus they can be guarantee that the cmpxchg_double
@@ -1934,7 +1911,6 @@ redo: 
	 */

	tid = c->tid;

	barrier();

#endif



	object = c->freelist;

	if (unlikely(!object || !node_match(c, node)))
@@ -1942,7 +1918,6 @@ redo: 
		object = __slab_alloc(s, gfpflags, node, addr, c);



	else {

#ifdef CONFIG_CMPXCHG_LOCAL

		/*

		 * The cmpxchg will only match if there was no additonal

		 * operation and if we are on the right processor.
@@ -1963,16 +1938,9 @@ redo: 
			note_cmpxchg_failure("slab_alloc", s, tid);

			goto redo;

		}

#else

		c->freelist = get_freepointer(s, object);

#endif

		stat(s, ALLOC_FASTPATH);

	}



#ifndef CONFIG_CMPXCHG_LOCAL

	local_irq_restore(flags);

#endif



	if (unlikely(gfpflags & __GFP_ZERO) && object)

		memset(object, 0, s->objsize);
@@ -2049,11 +2017,9 @@ static void __slab_free(struct kmem_cache *s, struct page *page, 
{

	void *prior;

	void **object = (void *)x;

#ifdef CONFIG_CMPXCHG_LOCAL

	unsigned long flags;



	local_irq_save(flags);

#endif

	slab_lock(page);

	stat(s, FREE_SLOWPATH);
@@ -2084,9 +2050,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page, 


out_unlock:

	slab_unlock(page);

#ifdef CONFIG_CMPXCHG_LOCAL

	local_irq_restore(flags);

#endif

	return;



slab_empty:
@@ -2098,9 +2062,7 @@ slab_empty: 
		stat(s, FREE_REMOVE_PARTIAL);

	}

	slab_unlock(page);

#ifdef CONFIG_CMPXCHG_LOCAL

	local_irq_restore(flags);

#endif

	stat(s, FREE_SLAB);

	discard_slab(s, page);

}
@@ -2121,20 +2083,11 @@ static __always_inline void slab_free(struct kmem_cache *s, 
{

	void **object = (void *)x;

	struct kmem_cache_cpu *c;

#ifdef CONFIG_CMPXCHG_LOCAL

	unsigned long tid;

#else

	unsigned long flags;

#endif



	slab_free_hook(s, x);



#ifndef CONFIG_CMPXCHG_LOCAL

	local_irq_save(flags);



#else

redo:

#endif



	/*

	 * Determine the currently cpus per cpu slab.
@@ -2144,15 +2097,12 @@ redo: 
	 */

	c = __this_cpu_ptr(s->cpu_slab);



#ifdef CONFIG_CMPXCHG_LOCAL

	tid = c->tid;

	barrier();

#endif



	if (likely(page == c->page && c->node != NUMA_NO_NODE)) {

		set_freepointer(s, object, c->freelist);



#ifdef CONFIG_CMPXCHG_LOCAL

		if (unlikely(!this_cpu_cmpxchg_double(

				s->cpu_slab->freelist, s->cpu_slab->tid,

				c->freelist, tid,
@@ -2161,16 +2111,10 @@ redo: 
			note_cmpxchg_failure("slab_free", s, tid);

			goto redo;

		}

#else

		c->freelist = object;

#endif

		stat(s, FREE_FASTPATH);

	} else

		__slab_free(s, page, x, addr);



#ifndef CONFIG_CMPXCHG_LOCAL

	local_irq_restore(flags);

#endif

}



void kmem_cache_free(struct kmem_cache *s, void *x)

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