blob: 4264814cabc926c623f47b5b1a9b70f5578f3664 [file] [log] [blame]
/*
* Copyright 2010 Marek Olšák <maraeo@gmail.com>
* Copyright 2016 Advanced Micro Devices, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* on the rights to use, copy, modify, merge, publish, distribute, sub
* license, and/or sell copies of the Software, and to permit persons to whom
* the Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
* THE AUTHOR(S) AND/OR THEIR SUPPLIERS BE LIABLE FOR ANY CLAIM,
* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
* OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
* USE OR OTHER DEALINGS IN THE SOFTWARE. */
#include "slab.h"
#include "macros.h"
#include "u_atomic.h"
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#define ALIGN(value, align) (((value) + (align) - 1) & ~((align) - 1))
#define SLAB_MAGIC_ALLOCATED 0xcafe4321
#define SLAB_MAGIC_FREE 0x7ee01234
#ifdef DEBUG
#define SET_MAGIC(element, value) (element)->magic = (value)
#define CHECK_MAGIC(element, value) assert((element)->magic == (value))
#else
#define SET_MAGIC(element, value)
#define CHECK_MAGIC(element, value)
#endif
/* One array element within a big buffer. */
struct slab_element_header {
/* The next element in the free or migrated list. */
struct slab_element_header *next;
/* This is either
* - a pointer to the child pool to which this element belongs, or
* - a pointer to the orphaned page of the element, with the least
* significant bit set to 1.
*/
intptr_t owner;
#ifdef DEBUG
intptr_t magic;
#endif
};
/* The page is an array of allocations in one block. */
struct slab_page_header {
union {
/* Next page in the same child pool. */
struct slab_page_header *next;
/* Number of remaining, non-freed elements (for orphaned pages). */
unsigned num_remaining;
} u;
/* Memory after the last member is dedicated to the page itself.
* The allocated size is always larger than this structure.
*/
};
static struct slab_element_header *
slab_get_element(struct slab_parent_pool *parent,
struct slab_page_header *page, unsigned index)
{
return (struct slab_element_header*)
((uint8_t*)&page[1] + (parent->element_size * index));
}
/* The given object/element belongs to an orphaned page (i.e. the owning child
* pool has been destroyed). Mark the element as freed and free the whole page
* when no elements are left in it.
*/
static void
slab_free_orphaned(struct slab_element_header *elt)
{
struct slab_page_header *page;
assert(elt->owner & 1);
page = (struct slab_page_header *)(elt->owner & ~(intptr_t)1);
if (!p_atomic_dec_return(&page->u.num_remaining))
free(page);
}
/**
* Create a parent pool for the allocation of same-sized objects.
*
* \param item_size Size of one object.
* \param num_items Number of objects to allocate at once.
*/
void
slab_create_parent(struct slab_parent_pool *parent,
unsigned item_size,
unsigned num_items)
{
mtx_init(&parent->mutex, mtx_plain);
parent->element_size = ALIGN(sizeof(struct slab_element_header) + item_size,
sizeof(intptr_t));
parent->num_elements = num_items;
}
void
slab_destroy_parent(struct slab_parent_pool *parent)
{
mtx_destroy(&parent->mutex);
}
/**
* Create a child pool linked to the given parent.
*/
void slab_create_child(struct slab_child_pool *pool,
struct slab_parent_pool *parent)
{
pool->parent = parent;
pool->pages = NULL;
pool->free = NULL;
pool->migrated = NULL;
}
/**
* Destroy the child pool.
*
* Pages associated to the pool will be orphaned. They are eventually freed
* when all objects in them are freed.
*/
void slab_destroy_child(struct slab_child_pool *pool)
{
mtx_lock(&pool->parent->mutex);
while (pool->pages) {
struct slab_page_header *page = pool->pages;
pool->pages = page->u.next;
p_atomic_set(&page->u.num_remaining, pool->parent->num_elements);
for (unsigned i = 0; i < pool->parent->num_elements; ++i) {
struct slab_element_header *elt = slab_get_element(pool->parent, page, i);
p_atomic_set(&elt->owner, (intptr_t)page | 1);
}
}
while (pool->migrated) {
struct slab_element_header *elt = pool->migrated;
pool->migrated = elt->next;
slab_free_orphaned(elt);
}
mtx_unlock(&pool->parent->mutex);
while (pool->free) {
struct slab_element_header *elt = pool->free;
pool->free = elt->next;
slab_free_orphaned(elt);
}
/* Guard against use-after-free. */
pool->parent = NULL;
}
static bool
slab_add_new_page(struct slab_child_pool *pool)
{
struct slab_page_header *page = malloc(sizeof(struct slab_page_header) +
pool->parent->num_elements * pool->parent->element_size);
if (!page)
return false;
for (unsigned i = 0; i < pool->parent->num_elements; ++i) {
struct slab_element_header *elt = slab_get_element(pool->parent, page, i);
elt->owner = (intptr_t)pool;
assert(!(elt->owner & 1));
elt->next = pool->free;
pool->free = elt;
SET_MAGIC(elt, SLAB_MAGIC_FREE);
}
page->u.next = pool->pages;
pool->pages = page;
return true;
}
/**
* Allocate an object from the child pool. Single-threaded (i.e. the caller
* must ensure that no operation happens on the same child pool in another
* thread).
*/
void *
slab_alloc(struct slab_child_pool *pool)
{
struct slab_element_header *elt;
if (!pool->free) {
/* First, collect elements that belong to us but were freed from a
* different child pool.
*/
mtx_lock(&pool->parent->mutex);
pool->free = pool->migrated;
pool->migrated = NULL;
mtx_unlock(&pool->parent->mutex);
/* Now allocate a new page. */
if (!pool->free && !slab_add_new_page(pool))
return NULL;
}
elt = pool->free;
pool->free = elt->next;
CHECK_MAGIC(elt, SLAB_MAGIC_FREE);
SET_MAGIC(elt, SLAB_MAGIC_ALLOCATED);
return &elt[1];
}
/**
* Free an object allocated from the slab. Single-threaded (i.e. the caller
* must ensure that no operation happens on the same child pool in another
* thread).
*
* Freeing an object in a different child pool from the one where it was
* allocated is allowed, as long the pool belong to the same parent. No
* additional locking is required in this case.
*/
void slab_free(struct slab_child_pool *pool, void *ptr)
{
struct slab_element_header *elt = ((struct slab_element_header*)ptr - 1);
intptr_t owner_int;
CHECK_MAGIC(elt, SLAB_MAGIC_ALLOCATED);
SET_MAGIC(elt, SLAB_MAGIC_FREE);
if (p_atomic_read(&elt->owner) == (intptr_t)pool) {
/* This is the simple case: The caller guarantees that we can safely
* access the free list.
*/
elt->next = pool->free;
pool->free = elt;
return;
}
/* The slow case: migration or an orphaned page. */
mtx_lock(&pool->parent->mutex);
/* Note: we _must_ re-read elt->owner here because the owning child pool
* may have been destroyed by another thread in the meantime.
*/
owner_int = p_atomic_read(&elt->owner);
if (!(owner_int & 1)) {
struct slab_child_pool *owner = (struct slab_child_pool *)owner_int;
elt->next = owner->migrated;
owner->migrated = elt;
mtx_unlock(&pool->parent->mutex);
} else {
mtx_unlock(&pool->parent->mutex);
slab_free_orphaned(elt);
}
}
/**
* Allocate an object from the slab. Single-threaded (no mutex).
*/
void *
slab_alloc_st(struct slab_mempool *pool)
{
return slab_alloc(&pool->child);
}
/**
* Free an object allocated from the slab. Single-threaded (no mutex).
*/
void
slab_free_st(struct slab_mempool *pool, void *ptr)
{
slab_free(&pool->child, ptr);
}
void
slab_destroy(struct slab_mempool *pool)
{
slab_destroy_child(&pool->child);
slab_destroy_parent(&pool->parent);
}
/**
* Create an allocator for same-sized objects.
*
* \param item_size Size of one object.
* \param num_items Number of objects to allocate at once.
*/
void
slab_create(struct slab_mempool *pool,
unsigned item_size,
unsigned num_items)
{
slab_create_parent(&pool->parent, item_size, num_items);
slab_create_child(&pool->child, &pool->parent);
}