Commit 9c824b6a authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu: make sure chunk->map array has available space 



An allocation attempt may require extending chunk->map array which
requires GFP_KERNEL context which isn't available for atomic
allocations.  This patch ensures that chunk->map array usually keeps
some amount of available space by directly allocating buffer space
during GFP_KERNEL allocations and scheduling async extension during
atomic ones.  This should make atomic allocation failures from map
space exhaustion rare.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 5835d96e

mm/percpu.c

+45 −8
Original line number Diff line number Diff line
@@ -76,6 +76,8 @@ 


#define PCPU_SLOT_BASE_SHIFT		5	/* 1-31 shares the same slot */

#define PCPU_DFL_MAP_ALLOC		16	/* start a map with 16 ents */

#define PCPU_ATOMIC_MAP_MARGIN_LOW	32

#define PCPU_ATOMIC_MAP_MARGIN_HIGH	64



#ifdef CONFIG_SMP

/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
@@ -102,9 +104,12 @@ struct pcpu_chunk { 
	int			free_size;	/* free bytes in the chunk */

	int			contig_hint;	/* max contiguous size hint */

	void			*base_addr;	/* base address of this chunk */



	int			map_used;	/* # of map entries used before the sentry */

	int			map_alloc;	/* # of map entries allocated */

	int			*map;		/* allocation map */

	struct work_struct	map_extend_work;/* async ->map[] extension */



	void			*data;		/* chunk data */

	int			first_free;	/* no free below this */

	bool			immutable;	/* no [de]population allowed */
@@ -318,9 +323,14 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot) 
/**

 * pcpu_need_to_extend - determine whether chunk area map needs to be extended

 * @chunk: chunk of interest

 * @is_atomic: the allocation context

 *

 * Determine whether area map of @chunk needs to be extended to

 * accommodate a new allocation.

 * Determine whether area map of @chunk needs to be extended.  If

 * @is_atomic, only the amount necessary for a new allocation is

 * considered; however, async extension is scheduled if the left amount is

 * low.  If !@is_atomic, it aims for more empty space.  Combined, this

 * ensures that the map is likely to have enough available space to

 * accomodate atomic allocations which can't extend maps directly.

 *

 * CONTEXT:

 * pcpu_lock.
@@ -329,15 +339,25 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot) 
 * New target map allocation length if extension is necessary, 0

 * otherwise.

 */

static int pcpu_need_to_extend(struct pcpu_chunk *chunk)

static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic)

{

	int new_alloc;

	int margin, new_alloc;



	if (is_atomic) {

		margin = 3;



	if (chunk->map_alloc >= chunk->map_used + 3)

		if (chunk->map_alloc <

		    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW)

			schedule_work(&chunk->map_extend_work);

	} else {

		margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;

	}



	if (chunk->map_alloc >= chunk->map_used + margin)

		return 0;



	new_alloc = PCPU_DFL_MAP_ALLOC;

	while (new_alloc < chunk->map_used + 3)

	while (new_alloc < chunk->map_used + margin)

		new_alloc *= 2;



	return new_alloc;
@@ -394,6 +414,20 @@ out_unlock: 
	return 0;

}



static void pcpu_map_extend_workfn(struct work_struct *work)

{

	struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk,

						map_extend_work);

	int new_alloc;



	spin_lock_irq(&pcpu_lock);

	new_alloc = pcpu_need_to_extend(chunk, false);

	spin_unlock_irq(&pcpu_lock);



	if (new_alloc)

		pcpu_extend_area_map(chunk, new_alloc);

}



/**

 * pcpu_fit_in_area - try to fit the requested allocation in a candidate area

 * @chunk: chunk the candidate area belongs to
@@ -647,6 +681,7 @@ static struct pcpu_chunk *pcpu_alloc_chunk(void) 
	chunk->map_used = 1;



	INIT_LIST_HEAD(&chunk->list);

	INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn);

	chunk->free_size = pcpu_unit_size;

	chunk->contig_hint = pcpu_unit_size;
@@ -767,7 +802,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, 
			goto fail_unlock;

		}



		while ((new_alloc = pcpu_need_to_extend(chunk))) {

		while ((new_alloc = pcpu_need_to_extend(chunk, is_atomic))) {

			spin_unlock_irqrestore(&pcpu_lock, flags);

			if (is_atomic ||

			    pcpu_extend_area_map(chunk, new_alloc) < 0) {
@@ -792,7 +827,7 @@ restart: 
			if (size > chunk->contig_hint)

				continue;



			new_alloc = pcpu_need_to_extend(chunk);

			new_alloc = pcpu_need_to_extend(chunk, is_atomic);

			if (new_alloc) {

				if (is_atomic)

					continue;
@@ -1418,6 +1453,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, 
	 */

	schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);

	INIT_LIST_HEAD(&schunk->list);

	INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn);

	schunk->base_addr = base_addr;

	schunk->map = smap;

	schunk->map_alloc = ARRAY_SIZE(smap);
@@ -1446,6 +1482,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, 
	if (dyn_size) {

		dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);

		INIT_LIST_HEAD(&dchunk->list);

		INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn);

		dchunk->base_addr = base_addr;

		dchunk->map = dmap;

		dchunk->map_alloc = ARRAY_SIZE(dmap);

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