[net-next-2.6.git] / lib / flex_array.c

/*
 * Flexible array managed in PAGE_SIZE parts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright IBM Corporation, 2009
 *
 * Author: Dave Hansen <dave@linux.vnet.ibm.com>
 */

#include <linux/flex_array.h>
#include <linux/slab.h>
#include <linux/stddef.h>

struct flex_array_part {
	char elements[FLEX_ARRAY_PART_SIZE];
};

/*
 * If a user requests an allocation which is small
 * enough, we may simply use the space in the
 * flex_array->parts[] array to store the user
 * data.
 */
static inline int elements_fit_in_base(struct flex_array *fa)
{
	int data_size = fa->element_size * fa->total_nr_elements;
	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
		return 1;
	return 0;
}

/**
 * flex_array_alloc - allocate a new flexible array
 * @element_size:	the size of individual elements in the array
 * @total:		total number of elements that this should hold
 * @flags:		page allocation flags to use for base array
 *
 * Note: all locking must be provided by the caller.
 *
 * @total is used to size internal structures.  If the user ever
 * accesses any array indexes >=@total, it will produce errors.
 *
 * The maximum number of elements is defined as: the number of
 * elements that can be stored in a page times the number of
 * page pointers that we can fit in the base structure or (using
 * integer math):
 *
 * 	(PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
 *
 * Here's a table showing example capacities.  Note that the maximum
 * index that the get/put() functions is just nr_objects-1.   This
 * basically means that you get 4MB of storage on 32-bit and 2MB on
 * 64-bit.
 *
 *
 * Element size | Objects | Objects |
 * PAGE_SIZE=4k |  32-bit |  64-bit |
 * ---------------------------------|
 *      1 bytes | 4186112 | 2093056 |
 *      2 bytes | 2093056 | 1046528 |
 *      3 bytes | 1395030 |  697515 |
 *      4 bytes | 1046528 |  523264 |
 *     32 bytes |  130816 |   65408 |
 *     33 bytes |  126728 |   63364 |
 *   2048 bytes |    2044 |    1022 |
 *   2049 bytes |    1022 |     511 |
 *       void * | 1046528 |  261632 |
 *
 * Since 64-bit pointers are twice the size, we lose half the
 * capacity in the base structure.  Also note that no effort is made
 * to efficiently pack objects across page boundaries.
 */
struct flex_array *flex_array_alloc(int element_size, unsigned int total,
					gfp_t flags)
{
	struct flex_array *ret;
	int max_size = FLEX_ARRAY_NR_BASE_PTRS *
				FLEX_ARRAY_ELEMENTS_PER_PART(element_size);

	/* max_size will end up 0 if element_size > PAGE_SIZE */
	if (total > max_size)
		return NULL;
	ret = kzalloc(sizeof(struct flex_array), flags);
	if (!ret)
		return NULL;
	ret->element_size = element_size;
	ret->total_nr_elements = total;
	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
		memset(&ret->parts[0], FLEX_ARRAY_FREE,
						FLEX_ARRAY_BASE_BYTES_LEFT);
	return ret;
}

static int fa_element_to_part_nr(struct flex_array *fa,
					unsigned int element_nr)
{
	return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
}

/**
 * flex_array_free_parts - just free the second-level pages
 * @fa:		the flex array from which to free parts
 *
 * This is to be used in cases where the base 'struct flex_array'
 * has been statically allocated and should not be free.
 */
void flex_array_free_parts(struct flex_array *fa)
{
	int part_nr;

	if (elements_fit_in_base(fa))
		return;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
		kfree(fa->parts[part_nr]);
}

void flex_array_free(struct flex_array *fa)
{
	flex_array_free_parts(fa);
	kfree(fa);
}

static unsigned int index_inside_part(struct flex_array *fa,
					unsigned int element_nr)
{
	unsigned int part_offset;

	part_offset = element_nr %
				FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
	return part_offset * fa->element_size;
}

static struct flex_array_part *
__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
{
	struct flex_array_part *part = fa->parts[part_nr];
	if (!part) {
		part = kmalloc(sizeof(struct flex_array_part), flags);
		if (!part)
			return NULL;
		if (!(flags & __GFP_ZERO))
			memset(part, FLEX_ARRAY_FREE,
				sizeof(struct flex_array_part));
		fa->parts[part_nr] = part;
	}
	return part;
}

/**
 * flex_array_put - copy data into the array at @element_nr
 * @fa:		the flex array to copy data into
 * @element_nr:	index of the position in which to insert
 * 		the new element.
 * @src:	address of data to copy into the array
 * @flags:	page allocation flags to use for array expansion
 *
 *
 * Note that this *copies* the contents of @src into
 * the array.  If you are trying to store an array of
 * pointers, make sure to pass in &ptr instead of ptr.
 * You may instead wish to use the flex_array_put_ptr()
 * helper function.
 *
 * Locking must be provided by the caller.
 */
int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
			gfp_t flags)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	dst = &part->elements[index_inside_part(fa, element_nr)];
	memcpy(dst, src, fa->element_size);
	return 0;
}

/**
 * flex_array_clear - clear element in array at @element_nr
 * @fa:		the flex array of the element.
 * @element_nr:	index of the position to clear.
 *
 * Locking must be provided by the caller.
 */
int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = fa->parts[part_nr];
		if (!part)
			return -EINVAL;
	}
	dst = &part->elements[index_inside_part(fa, element_nr)];
	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
	return 0;
}

/**
 * flex_array_prealloc - guarantee that array space exists
 * @fa:		the flex array for which to preallocate parts
 * @start:	index of first array element for which space is allocated
 * @end:	index of last (inclusive) element for which space is allocated
 * @flags:	page allocation flags
 *
 * This will guarantee that no future calls to flex_array_put()
 * will allocate memory.  It can be used if you are expecting to
 * be holding a lock or in some atomic context while writing
 * data into the array.
 *
 * Locking must be provided by the caller.
 */
int flex_array_prealloc(struct flex_array *fa, unsigned int start,
			unsigned int end, gfp_t flags)
{
	int start_part;
	int end_part;
	int part_nr;
	struct flex_array_part *part;

	if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		return 0;
	start_part = fa_element_to_part_nr(fa, start);
	end_part = fa_element_to_part_nr(fa, end);
	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	return 0;
}

/**
 * flex_array_get - pull data back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns a pointer to the data at index @element_nr.  Note
 * that this is a copy of the data that was passed in.  If you
 * are using this to store pointers, you'll get back &ptr.  You
 * may instead wish to use the flex_array_get_ptr helper.
 *
 * Locking must be provided by the caller.
 */
void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;

	if (element_nr >= fa->total_nr_elements)
		return NULL;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = fa->parts[part_nr];
		if (!part)
			return NULL;
	}
	return &part->elements[index_inside_part(fa, element_nr)];
}

/**
 * flex_array_get_ptr - pull a ptr back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns the pointer placed in the flex array at element_nr using
 * flex_array_put_ptr().  This function should not be called if the
 * element in question was not set using the _put_ptr() helper.
 */
void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
{
	void **tmp;

	tmp = flex_array_get(fa, element_nr);
	if (!tmp)
		return NULL;

	return *tmp;
}

static int part_is_free(struct flex_array_part *part)
{
	int i;

	for (i = 0; i < sizeof(struct flex_array_part); i++)
		if (part->elements[i] != FLEX_ARRAY_FREE)
			return 0;
	return 1;
}

/**
 * flex_array_shrink - free unused second-level pages
 * @fa:		the flex array to shrink
 *
 * Frees all second-level pages that consist solely of unused
 * elements.  Returns the number of pages freed.
 *
 * Locking must be provided by the caller.
 */
int flex_array_shrink(struct flex_array *fa)
{
	struct flex_array_part *part;
	int part_nr;
	int ret = 0;

	if (elements_fit_in_base(fa))
		return ret;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
		part = fa->parts[part_nr];
		if (!part)
			continue;
		if (part_is_free(part)) {
			fa->parts[part_nr] = NULL;
			kfree(part);
			ret++;
		}
	}
	return ret;
}
Commit	Line	Data
534acc05 DH	1	/*
	2	* Flexible array managed in PAGE_SIZE parts
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License as published by
	6	* the Free Software Foundation; either version 2 of the License, or
	7	* (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, write to the Free Software
	16	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*
	18	* Copyright IBM Corporation, 2009
	19	*
	20	* Author: Dave Hansen <dave@linux.vnet.ibm.com>
	21	*/
	22
	23	#include <linux/flex_array.h>
	24	#include <linux/slab.h>
	25	#include <linux/stddef.h>
	26
	27	struct flex_array_part {
	28	char elements[FLEX_ARRAY_PART_SIZE];
	29	};
	30
534acc05 DH	31	/*
	32	* If a user requests an allocation which is small
	33	* enough, we may simply use the space in the
	34	* flex_array->parts[] array to store the user
	35	* data.
	36	*/
	37	static inline int elements_fit_in_base(struct flex_array *fa)
	38	{
	39	int data_size = fa->element_size * fa->total_nr_elements;
45b588d6	40	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
534acc05 DH	41	return 1;
	42	return 0;
	43	}
	44
	45	/**
	46	* flex_array_alloc - allocate a new flexible array
	47	* @element_size: the size of individual elements in the array
	48	* @total: total number of elements that this should hold
fc0d8d94	49	* @flags: page allocation flags to use for base array
534acc05 DH	50	*
	51	* Note: all locking must be provided by the caller.
	52	*
	53	* @total is used to size internal structures. If the user ever
	54	* accesses any array indexes >=@total, it will produce errors.
	55	*
	56	* The maximum number of elements is defined as: the number of
	57	* elements that can be stored in a page times the number of
	58	* page pointers that we can fit in the base structure or (using
	59	* integer math):
	60	*
	61	* (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
	62	*
	63	* Here's a table showing example capacities. Note that the maximum
	64	* index that the get/put() functions is just nr_objects-1. This
	65	* basically means that you get 4MB of storage on 32-bit and 2MB on
	66	* 64-bit.
	67	*
	68	*
	69	* Element size \| Objects \| Objects \|
	70	* PAGE_SIZE=4k \| 32-bit \| 64-bit \|
	71	* ---------------------------------\|
	72	* 1 bytes \| 4186112 \| 2093056 \|
	73	* 2 bytes \| 2093056 \| 1046528 \|
	74	* 3 bytes \| 1395030 \| 697515 \|
	75	* 4 bytes \| 1046528 \| 523264 \|
	76	* 32 bytes \| 130816 \| 65408 \|
	77	* 33 bytes \| 126728 \| 63364 \|
	78	* 2048 bytes \| 2044 \| 1022 \|
	79	* 2049 bytes \| 1022 \| 511 \|
	80	* void * \| 1046528 \| 261632 \|
	81	*
	82	* Since 64-bit pointers are twice the size, we lose half the
	83	* capacity in the base structure. Also note that no effort is made
	84	* to efficiently pack objects across page boundaries.
	85	*/
b62e408c DR	86	struct flex_array *flex_array_alloc(int element_size, unsigned int total,
b62e408c DR	87	gfp_t flags)
534acc05 DH	88	{
534acc05 DH	89	struct flex_array *ret;
45b588d6 DR	90	int max_size = FLEX_ARRAY_NR_BASE_PTRS *
45b588d6 DR	91	FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
534acc05 DH	92
	93	/* max_size will end up 0 if element_size > PAGE_SIZE */
	94	if (total > max_size)
	95	return NULL;
	96	ret = kzalloc(sizeof(struct flex_array), flags);
	97	if (!ret)
	98	return NULL;
	99	ret->element_size = element_size;
	100	ret->total_nr_elements = total;
19da3dd1	101	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
e59464c7	102	memset(&ret->parts[0], FLEX_ARRAY_FREE,
45b588d6	103	FLEX_ARRAY_BASE_BYTES_LEFT);
534acc05 DH	104	return ret;
	105	}
	106
b62e408c DR	107	static int fa_element_to_part_nr(struct flex_array *fa,
b62e408c DR	108	unsigned int element_nr)
534acc05	109	{
45b588d6	110	return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
534acc05 DH	111	}
	112
	113	/**
	114	* flex_array_free_parts - just free the second-level pages
fc0d8d94	115	* @fa: the flex array from which to free parts
534acc05 DH	116	*
	117	* This is to be used in cases where the base 'struct flex_array'
	118	* has been statically allocated and should not be free.
	119	*/
	120	void flex_array_free_parts(struct flex_array *fa)
	121	{
	122	int part_nr;
534acc05 DH	123
	124	if (elements_fit_in_base(fa))
	125	return;
45b588d6	126	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
534acc05 DH	127	kfree(fa->parts[part_nr]);
	128	}
	129
	130	void flex_array_free(struct flex_array *fa)
	131	{
	132	flex_array_free_parts(fa);
	133	kfree(fa);
	134	}
	135
b62e408c DR	136	static unsigned int index_inside_part(struct flex_array *fa,
b62e408c DR	137	unsigned int element_nr)
534acc05	138	{
b62e408c	139	unsigned int part_offset;
534acc05	140
45b588d6 DR	141	part_offset = element_nr %
45b588d6 DR	142	FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
534acc05 DH	143	return part_offset * fa->element_size;
	144	}
	145
	146	static struct flex_array_part *
	147	__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
	148	{
	149	struct flex_array_part *part = fa->parts[part_nr];
	150	if (!part) {
19da3dd1	151	part = kmalloc(sizeof(struct flex_array_part), flags);
534acc05 DH	152	if (!part)
534acc05 DH	153	return NULL;
19da3dd1 DR	154	if (!(flags & __GFP_ZERO))
	155	memset(part, FLEX_ARRAY_FREE,
	156	sizeof(struct flex_array_part));
534acc05 DH	157	fa->parts[part_nr] = part;
	158	}
	159	return part;
	160	}
	161
	162	/**
	163	* flex_array_put - copy data into the array at @element_nr
fc0d8d94	164	* @fa: the flex array to copy data into
534acc05 DH	165	* @element_nr: index of the position in which to insert
534acc05 DH	166	* the new element.
fc0d8d94 DR	167	* @src: address of data to copy into the array
	168	* @flags: page allocation flags to use for array expansion
	169	*
534acc05 DH	170	*
	171	* Note that this copies the contents of @src into
	172	* the array. If you are trying to store an array of
	173	* pointers, make sure to pass in &ptr instead of ptr.
ea98eed9 EP	174	* You may instead wish to use the flex_array_put_ptr()
ea98eed9 EP	175	* helper function.
534acc05 DH	176	*
	177	* Locking must be provided by the caller.
	178	*/
b62e408c DR	179	int flex_array_put(struct flex_array fa, unsigned int element_nr, void src,
b62e408c DR	180	gfp_t flags)
534acc05 DH	181	{
	182	int part_nr = fa_element_to_part_nr(fa, element_nr);
	183	struct flex_array_part *part;
	184	void *dst;
	185
	186	if (element_nr >= fa->total_nr_elements)
	187	return -ENOSPC;
	188	if (elements_fit_in_base(fa))
	189	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	190	else {
534acc05	191	part = __fa_get_part(fa, part_nr, flags);
a30b595d DR	192	if (!part)
	193	return -ENOMEM;
	194	}
534acc05 DH	195	dst = &part->elements[index_inside_part(fa, element_nr)];
	196	memcpy(dst, src, fa->element_size);
	197	return 0;
	198	}
	199
e6de3988 DR	200	/**
e6de3988 DR	201	* flex_array_clear - clear element in array at @element_nr
fc0d8d94	202	* @fa: the flex array of the element.
e6de3988 DR	203	* @element_nr: index of the position to clear.
	204	*
	205	* Locking must be provided by the caller.
	206	*/
	207	int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
	208	{
	209	int part_nr = fa_element_to_part_nr(fa, element_nr);
	210	struct flex_array_part *part;
	211	void *dst;
	212
	213	if (element_nr >= fa->total_nr_elements)
	214	return -ENOSPC;
	215	if (elements_fit_in_base(fa))
	216	part = (struct flex_array_part *)&fa->parts[0];
	217	else {
	218	part = fa->parts[part_nr];
	219	if (!part)
	220	return -EINVAL;
	221	}
	222	dst = &part->elements[index_inside_part(fa, element_nr)];
19da3dd1	223	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
e6de3988 DR	224	return 0;
	225	}
	226
534acc05 DH	227	/**
534acc05 DH	228	* flex_array_prealloc - guarantee that array space exists
fc0d8d94	229	* @fa: the flex array for which to preallocate parts
534acc05 DH	230	* @start: index of first array element for which space is allocated
534acc05 DH	231	* @end: index of last (inclusive) element for which space is allocated
fc0d8d94	232	* @flags: page allocation flags
534acc05 DH	233	*
	234	* This will guarantee that no future calls to flex_array_put()
	235	* will allocate memory. It can be used if you are expecting to
	236	* be holding a lock or in some atomic context while writing
	237	* data into the array.
	238	*
	239	* Locking must be provided by the caller.
	240	*/
b62e408c DR	241	int flex_array_prealloc(struct flex_array *fa, unsigned int start,
b62e408c DR	242	unsigned int end, gfp_t flags)
534acc05 DH	243	{
	244	int start_part;
	245	int end_part;
	246	int part_nr;
	247	struct flex_array_part *part;
	248
	249	if (start >= fa->total_nr_elements \|\| end >= fa->total_nr_elements)
	250	return -ENOSPC;
	251	if (elements_fit_in_base(fa))
	252	return 0;
	253	start_part = fa_element_to_part_nr(fa, start);
	254	end_part = fa_element_to_part_nr(fa, end);
	255	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
	256	part = __fa_get_part(fa, part_nr, flags);
	257	if (!part)
	258	return -ENOMEM;
	259	}
	260	return 0;
	261	}
	262
	263	/**
	264	* flex_array_get - pull data back out of the array
fc0d8d94	265	* @fa: the flex array from which to extract data
534acc05 DH	266	* @element_nr: index of the element to fetch from the array
	267	*
	268	* Returns a pointer to the data at index @element_nr. Note
	269	* that this is a copy of the data that was passed in. If you
ea98eed9 EP	270	* are using this to store pointers, you'll get back &ptr. You
ea98eed9 EP	271	* may instead wish to use the flex_array_get_ptr helper.
534acc05 DH	272	*
	273	* Locking must be provided by the caller.
	274	*/
b62e408c	275	void flex_array_get(struct flex_array fa, unsigned int element_nr)
534acc05 DH	276	{
	277	int part_nr = fa_element_to_part_nr(fa, element_nr);
	278	struct flex_array_part *part;
534acc05 DH	279
	280	if (element_nr >= fa->total_nr_elements)
	281	return NULL;
534acc05 DH	282	if (elements_fit_in_base(fa))
534acc05 DH	283	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	284	else {
534acc05	285	part = fa->parts[part_nr];
a30b595d DR	286	if (!part)
	287	return NULL;
	288	}
534acc05 DH	289	return &part->elements[index_inside_part(fa, element_nr)];
534acc05 DH	290	}
4af5a2f7	291
ea98eed9 EP	292	/**
	293	* flex_array_get_ptr - pull a ptr back out of the array
	294	* @fa: the flex array from which to extract data
	295	* @element_nr: index of the element to fetch from the array
	296	*
	297	* Returns the pointer placed in the flex array at element_nr using
	298	* flex_array_put_ptr(). This function should not be called if the
	299	* element in question was not set using the _put_ptr() helper.
	300	*/
	301	void flex_array_get_ptr(struct flex_array fa, unsigned int element_nr)
	302	{
	303	void **tmp;
	304
	305	tmp = flex_array_get(fa, element_nr);
	306	if (!tmp)
	307	return NULL;
	308
	309	return *tmp;
	310	}
	311
4af5a2f7 DR	312	static int part_is_free(struct flex_array_part *part)
	313	{
	314	int i;
	315
	316	for (i = 0; i < sizeof(struct flex_array_part); i++)
	317	if (part->elements[i] != FLEX_ARRAY_FREE)
	318	return 0;
	319	return 1;
	320	}
	321
	322	/**
	323	* flex_array_shrink - free unused second-level pages
fc0d8d94	324	* @fa: the flex array to shrink
4af5a2f7 DR	325	*
	326	* Frees all second-level pages that consist solely of unused
	327	* elements. Returns the number of pages freed.
	328	*
	329	* Locking must be provided by the caller.
	330	*/
	331	int flex_array_shrink(struct flex_array *fa)
	332	{
	333	struct flex_array_part *part;
4af5a2f7 DR	334	int part_nr;
	335	int ret = 0;
	336
	337	if (elements_fit_in_base(fa))
	338	return ret;
45b588d6	339	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
4af5a2f7 DR	340	part = fa->parts[part_nr];
	341	if (!part)
	342	continue;
	343	if (part_is_free(part)) {
	344	fa->parts[part_nr] = NULL;
	345	kfree(part);
	346	ret++;
	347	}
	348	}
	349	return ret;
	350	}