lib/flex_array.c - kernel/msm-4.9 - Gitiles

 /*
  * 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>
 #include <linux/module.h>
 #include <linux/reciprocal_div.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 | 4177920 | 2088960 |
  *      2 bytes | 2088960 | 1044480 |
  *      3 bytes | 1392300 |  696150 |
  *      4 bytes | 1044480 |  522240 |
  *     32 bytes |  130560 |   65408 |
  *     33 bytes |  126480 |   63240 |
  *   2048 bytes |    2040 |    1020 |
  *   2049 bytes |    1020 |     510 |
  *       void * | 1044480 |  261120 |
  *
  * 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 elems_per_part = 0;
 	int reciprocal_elems = 0;
 	int max_size = 0;

 	if (element_size) {
 		elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
 		reciprocal_elems = reciprocal_value(elems_per_part);
 		max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
 	}

 	/* 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;
 	ret->elems_per_part = elems_per_part;
 	ret->reciprocal_elems = reciprocal_elems;
 	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
 		memset(&ret->parts[0], FLEX_ARRAY_FREE,
 						FLEX_ARRAY_BASE_BYTES_LEFT);
 	return ret;
 }
 EXPORT_SYMBOL(flex_array_alloc);

 static int fa_element_to_part_nr(struct flex_array *fa,
 					unsigned int element_nr)
 {
 	return reciprocal_divide(element_nr, fa->reciprocal_elems);
 }

 /**
  * 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]);
 }
 EXPORT_SYMBOL(flex_array_free_parts);

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

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

 	part_offset = element_nr - part_nr * fa->elems_per_part;
 	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 = 0;
 	struct flex_array_part *part;
 	void *dst;

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

 /**
  * 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 = 0;
 	struct flex_array_part *part;
 	void *dst;

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

 /**
  * 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
  * @nr_elements:	number of elements 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 nr_elements, gfp_t flags)
 {
 	int start_part;
 	int end_part;
 	int part_nr;
 	unsigned int end;
 	struct flex_array_part *part;

 	if (!start && !nr_elements)
 		return 0;
 	if (start >= fa->total_nr_elements)
 		return -ENOSPC;
 	if (!nr_elements)
 		return 0;

 	end = start + nr_elements - 1;

 	if (end >= fa->total_nr_elements)
 		return -ENOSPC;
 	if (!fa->element_size)
 		return 0;
 	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;
 }
 EXPORT_SYMBOL(flex_array_prealloc);

 /**
  * 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 = 0;
 	struct flex_array_part *part;

 	if (!fa->element_size)
 		return NULL;
 	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_nr = fa_element_to_part_nr(fa, element_nr);
 		part = fa->parts[part_nr];
 		if (!part)
 			return NULL;
 	}
 	return &part->elements[index_inside_part(fa, element_nr, part_nr)];
 }
 EXPORT_SYMBOL(flex_array_get);

 /**
  * 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;
 }
 EXPORT_SYMBOL(flex_array_get_ptr);

 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 (!fa->total_nr_elements || !fa->element_size)
 		return 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;
 }
 EXPORT_SYMBOL(flex_array_shrink);
	/*
	* 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>
	#include <linux/module.h>
	#include <linux/reciprocal_div.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 \| 4177920 \| 2088960 \|
	* 2 bytes \| 2088960 \| 1044480 \|
	* 3 bytes \| 1392300 \| 696150 \|
	* 4 bytes \| 1044480 \| 522240 \|
	* 32 bytes \| 130560 \| 65408 \|
	* 33 bytes \| 126480 \| 63240 \|
	* 2048 bytes \| 2040 \| 1020 \|
	* 2049 bytes \| 1020 \| 510 \|
	* void * \| 1044480 \| 261120 \|
	*
	* 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 elems_per_part = 0;
	int reciprocal_elems = 0;
	int max_size = 0;

	if (element_size) {
	elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
	reciprocal_elems = reciprocal_value(elems_per_part);
	max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
	}

	/* 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;
	ret->elems_per_part = elems_per_part;
	ret->reciprocal_elems = reciprocal_elems;
	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
	memset(&ret->parts[0], FLEX_ARRAY_FREE,
	FLEX_ARRAY_BASE_BYTES_LEFT);
	return ret;
	}
	EXPORT_SYMBOL(flex_array_alloc);

	static int fa_element_to_part_nr(struct flex_array *fa,
	unsigned int element_nr)
	{
	return reciprocal_divide(element_nr, fa->reciprocal_elems);
	}

	/**
	* 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]);
	}
	EXPORT_SYMBOL(flex_array_free_parts);

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

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

	part_offset = element_nr - part_nr * fa->elems_per_part;
	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 = 0;
	struct flex_array_part *part;
	void *dst;

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

	/**
	* 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 = 0;
	struct flex_array_part *part;
	void *dst;

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

	/**
	* 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
	* @nr_elements: number of elements 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 nr_elements, gfp_t flags)
	{
	int start_part;
	int end_part;
	int part_nr;
	unsigned int end;
	struct flex_array_part *part;

	if (!start && !nr_elements)
	return 0;
	if (start >= fa->total_nr_elements)
	return -ENOSPC;
	if (!nr_elements)
	return 0;

	end = start + nr_elements - 1;

	if (end >= fa->total_nr_elements)
	return -ENOSPC;
	if (!fa->element_size)
	return 0;
	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;
	}
	EXPORT_SYMBOL(flex_array_prealloc);

	/**
	* 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 = 0;
	struct flex_array_part *part;

	if (!fa->element_size)
	return NULL;
	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_nr = fa_element_to_part_nr(fa, element_nr);
	part = fa->parts[part_nr];
	if (!part)
	return NULL;
	}
	return &part->elements[index_inside_part(fa, element_nr, part_nr)];
	}
	EXPORT_SYMBOL(flex_array_get);

	/**
	* 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;
	}
	EXPORT_SYMBOL(flex_array_get_ptr);

	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 (!fa->total_nr_elements \|\| !fa->element_size)
	return 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;
	}
	EXPORT_SYMBOL(flex_array_shrink);