linux/lib/flex_array.c at master · rata/linux · GitHub

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* 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/export.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 max_size = 0;

struct reciprocal_value reciprocal_elems = { 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)

{

* if element_size == 0 we don't get here, so we never touch

* the zeroed fa->reciprocal_elems, which would yield invalid

* results

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);

linux/lib/flex_array.c at master · rata/linux · GitHub

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