tor/src/common/mempool.c

553 lines
18 KiB
C
Raw Normal View History

/* Copyright 2007 Nick Mathewson */
/* See LICENSE for licensing information */
/* $Id$ */
#if 1
/* Tor dependencies */
#include "orconfig.h"
#endif
#include <stdlib.h>
#include <string.h>
#define MEMPOOL_PRIVATE
#include "mempool.h"
/* OVERVIEW:
*
* This is an implementation of memory pools for Tor cells. It may be
* useful for you too.
*
* Generally, a memory pool is an allocation strategy optimized for large
* numbers of identically-sized objects. Rather than the elaborate arena
2007-05-25 21:41:31 +02:00
* and coalescing strategies you need to get good performance for a
* general-purpose malloc(), pools use a series of large memory "chunks",
* each of which is carved into a bunch of smaller "items" or
* "allocations".
*
* To get decent performance, you need to:
* - Minimize the number of times you hit the underlying allocator.
* - Try to keep accesses as local in memory as possible.
* - Try to keep the common case fast.
*
* Our implementation uses three lists of chunks per pool. Each chunk can
* be either "full" (no more room for items); "empty" (no items); or
* "used" (not full, not empty). There are independent doubly-linked
* lists for each state.
*
* CREDIT:
*
* I wrote this after looking at 3 or 4 other pooling allocators, but
* without copying. The strategy this most resembles (which is funny,
2007-05-25 21:41:31 +02:00
* since that's the one I looked at longest ago) is the pool allocator
* underlying Python's obmalloc code. Major differences from obmalloc's
* pools are:
* - We don't even try to be threadsafe.
* - We only handle objects of one size.
* - Our list of empty chunks is doubly-linked, not singly-linked.
* (This could change pretty easily; it's only doubly-linked for
* consistency.)
* - We keep a list of full chunks (so we can have a "nuke everything"
* function). Obmalloc's pools leave full chunks to float unanchored.
*
* [XXXX020 Another way to support 'nuke everything' would be to keep
* _all_ the chunks in a doubly-linked-list. This would have more
* space overhead per chunk, but less pointer manipulation overhead
* than the current approach.]
*
* LIMITATIONS:
* - Not even slightly threadsafe.
* - Likes to have lots of items per chunks.
* - One pointer overhead per allocated thing. (The alternative is
* something like glib's use of an RB-tree to keep track of what
* chunk any given piece of memory is in.)
* - Only aligns allocated things to void* level: redefign ALIGNMENT_TYPE
* if you need doubles.
* - Could probably be optimized a bit; the representation contains
* a bit more info than it really needs to have.
* - probably, chunks should always be a power of 2.
*/
#if 1
/* Tor dependencies */
#include "orconfig.h"
#include "util.h"
#include "compat.h"
#include "log.h"
#define ALLOC(x) tor_malloc(x)
#define FREE(x) tor_free(x)
#define ASSERT(x) tor_assert(x)
#undef ALLOC_CAN_RETURN_NULL
#define TOR
/* End Tor dependencies */
#else
/* If you're not building this as part of Tor, you'll want to define the
* following macros. For now, these should do as defaults.
*/
#include <assert.h>
#define PREDICT_UNLIKELY(x) (x)
#define PREDICT_LIKELY(x) (x)
#define ALLOC(x) malloc(x)
#define FREE(x) free(x)
#define STRUCT_OFFSET(tp, member) \
((off_t) (((char*)&((tp*)0)->member)-(char*)0))
#define ASSERT(x) assert(x)
#define ALLOC_CAN_RETURN_NULL
#endif
/* Tuning parameters */
/** Largest type that we need to ensure returned memory items are aligned to.
* Change this to "double" if we need to be safe for structs with doubles. */
#define ALIGNMENT_TYPE void *
2007-05-25 21:41:31 +02:00
/** Increment that we need to align allocated. */
#define ALIGNMENT sizeof(ALIGNMENT_TYPE)
/** Largest memory chunk that we should allocate. */
#define MAX_CHUNK (8*(1L<<20))
/** Smallest memory chunk size that we should allocate. */
#define MIN_CHUNK 4096
typedef struct mp_allocated_t mp_allocated_t;
typedef struct mp_chunk_t mp_chunk_t;
/** Holds a single allocated item, allocated as part of a chunk. */
struct mp_allocated_t {
/** The chunk that this item is allocated in. This adds overhead to each
* allocated item, thus making this implementation inappropriate for
* very small items. */
mp_chunk_t *in_chunk;
union {
/** If this item is free, the next item on the free list. */
mp_allocated_t *next_free;
/** If this item is not free, the actual memory contents of this item.
* (Not actual size.) */
char mem[1];
/** An extra element to the union to insure correct alignment. */
ALIGNMENT_TYPE _dummy;
} u;
};
/** 'Magic' value used to detect memory corruption. */
#define MP_CHUNK_MAGIC 0x09870123
/** A chunk of memory. Chunks come from malloc; we use them */
struct mp_chunk_t {
unsigned long magic; /**< Must be MP_CHUNK_MAGIC if this chunk is valid. */
mp_chunk_t *next; /**< The next free, used, or full chunk in sequence. */
mp_chunk_t *prev; /**< The previous free, used, or full chunk in sequence. */
2007-05-25 21:41:31 +02:00
mp_pool_t *pool; /**< The pool that this chunk is part of. */
/** First free item in the freelist for this chunk. Note that this may be
* NULL even if this chunk is not at capacity: if so, the free memory at
* next_mem has not yet been carved into items.
*/
mp_allocated_t *first_free;
2007-05-25 21:41:31 +02:00
int n_allocated; /**< Number of currently allocated items in this chunk. */
int capacity; /**< Number of items that can be fit into this chunk. */
size_t mem_size; /**< Number of usable bytes in mem. */
char *next_mem; /**< Pointer into part of <b>mem</b> not yet carved up. */
char mem[1]; /**< Storage for this chunk. (Not actual size.) */
};
/** Number of extra bytes needed beyond mem_size to allocate a chunk. */
#define CHUNK_OVERHEAD (sizeof(mp_chunk_t)-1)
/** Given a pointer to a mp_allocated_t, return a pointer to the memory
* item it holds. */
#define A2M(a) (&(a)->u.mem)
/** Given a pointer to a memory_item_t, return a pointer to its enclosing
* mp_allocated_t. */
#define M2A(p) ( ((char*)p) - STRUCT_OFFSET(mp_allocated_t, u.mem) )
#ifdef ALLOC_CAN_RETURN_NULL
/** If our ALLOC() macro can return NULL, check whether <b>x</b> is NULL,
* and if so, return NULL. */
#define CHECK_ALLOC(x) \
if (PREDICT_UNLIKELY(!x)) { return NULL; }
#else
/** If our ALLOC() macro can't return NULL, do nothing. */
#define CHECK_ALLOC(x)
#endif
/** Helper: Allocate and return a new memory chunk for <b>pool</b>. Does not
* link the chunk into any list. */
static mp_chunk_t *
mp_chunk_new(mp_pool_t *pool)
{
size_t sz = pool->new_chunk_capacity * pool->item_alloc_size;
mp_chunk_t *chunk = ALLOC(CHUNK_OVERHEAD + sz);
CHECK_ALLOC(chunk);
memset(chunk, 0, sizeof(mp_chunk_t)); /* Doesn't clear the whole thing. */
chunk->magic = MP_CHUNK_MAGIC;
chunk->capacity = pool->new_chunk_capacity;
chunk->mem_size = sz;
chunk->next_mem = chunk->mem;
chunk->pool = pool;
return chunk;
}
/** Return an newly allocated item from <b>pool</b>. */
void *
mp_pool_get(mp_pool_t *pool)
{
mp_chunk_t *chunk;
mp_allocated_t *allocated;
if (PREDICT_LIKELY(pool->used_chunks != NULL)) {
/* Common case: there is some chunk that is neither full nor empty. Use
* that one. (We can't use the full ones, obviously, and we should fill
* up the used ones before we start on any empty ones. */
chunk = pool->used_chunks;
} else if (pool->empty_chunks) {
/* We have no used chunks, but we have an empty chunk that we haven't
* freed yet: use that. (We pull from the front of the list, which should
* get us the most recently emptied chunk.) */
chunk = pool->empty_chunks;
/* Remove the chunk from the empty list. */
pool->empty_chunks = chunk->next;
if (chunk->next)
chunk->next->prev = NULL;
/* Put the chunk on the 'used' list*/
chunk->next = pool->used_chunks;
if (chunk->next)
chunk->next->prev = chunk;
pool->used_chunks = chunk;
ASSERT(!chunk->prev);
--pool->n_empty_chunks;
if (pool->n_empty_chunks < pool->min_empty_chunks)
pool->min_empty_chunks = pool->n_empty_chunks;
} else {
/* We have no used or empty chunks: allocate a new chunk. */
chunk = mp_chunk_new(pool);
CHECK_ALLOC(chunk);
/* Add the new chunk to the used list. */
chunk->next = pool->used_chunks;
if (chunk->next)
chunk->next->prev = chunk;
pool->used_chunks = chunk;
ASSERT(!chunk->prev);
}
ASSERT(chunk->n_allocated < chunk->capacity);
if (chunk->first_free) {
/* If there's anything on the chunk's freelist, unlink it and use it. */
allocated = chunk->first_free;
chunk->first_free = allocated->u.next_free;
allocated->u.next_free = NULL; /* For debugging; not really needed. */
ASSERT(allocated->in_chunk == chunk);
} else {
/* Otherwise, the chunk had better have some free space left on it. */
ASSERT(chunk->next_mem + pool->item_alloc_size <=
chunk->mem + chunk->mem_size);
/* Good, it did. Let's carve off a bit of that free space, and use
* that. */
allocated = (void*)chunk->next_mem;
chunk->next_mem += pool->item_alloc_size;
allocated->in_chunk = chunk;
allocated->u.next_free = NULL; /* For debugging; not really needed. */
}
++chunk->n_allocated;
if (PREDICT_UNLIKELY(chunk->n_allocated == chunk->capacity)) {
/* This chunk just became full. */
ASSERT(chunk == pool->used_chunks);
ASSERT(chunk->prev == NULL);
/* Take it off the used list. */
pool->used_chunks = chunk->next;
if (chunk->next)
chunk->next->prev = NULL;
/* Put it on the full list. */
chunk->next = pool->full_chunks;
if (chunk->next)
chunk->next->prev = chunk;
pool->full_chunks = chunk;
}
/* And return the memory portion of the mp_allocated_t. */
return A2M(allocated);
}
/** Return an allocated memory item to its memory pool. */
void
mp_pool_release(void *item)
{
mp_allocated_t *allocated = (void*) M2A(item);
mp_chunk_t *chunk = allocated->in_chunk;
ASSERT(chunk);
ASSERT(chunk->magic == MP_CHUNK_MAGIC);
ASSERT(chunk->n_allocated > 0);
allocated->u.next_free = chunk->first_free;
chunk->first_free = allocated;
if (PREDICT_UNLIKELY(chunk->n_allocated == chunk->capacity)) {
/* This chunk was full and is about to be used. */
mp_pool_t *pool = chunk->pool;
/* unlink from the full list */
if (chunk->prev)
chunk->prev->next = chunk->next;
if (chunk->next)
chunk->next->prev = chunk->prev;
if (chunk == pool->full_chunks)
pool->full_chunks = chunk->next;
/* link to the used list. */
chunk->next = pool->used_chunks;
chunk->prev = NULL;
if (chunk->next)
chunk->next->prev = chunk;
pool->used_chunks = chunk;
} else if (PREDICT_UNLIKELY(chunk->n_allocated == 1)) {
/* This was used and is about to be empty. */
mp_pool_t *pool = chunk->pool;
/* Unlink from the used list */
if (chunk->prev)
chunk->prev->next = chunk->next;
if (chunk->next)
chunk->next->prev = chunk->prev;
if (chunk == pool->used_chunks)
pool->used_chunks = chunk->next;
/* Link to the empty list */
chunk->next = pool->empty_chunks;
chunk->prev = NULL;
if (chunk->next)
chunk->next->prev = chunk;
pool->empty_chunks = chunk;
/* Reset the guts of this chunk to defragment it, in case it gets
* used again. */
chunk->first_free = NULL;
chunk->next_mem = chunk->mem;
++pool->n_empty_chunks;
}
--chunk->n_allocated;
}
/** Allocate a new memory pool to hold items of size <b>item_size</b>. We'll
* try to fit about <b>chunk_capacity</b> bytes in each chunk. */
mp_pool_t *
mp_pool_new(size_t item_size, size_t chunk_capacity)
{
mp_pool_t *pool;
size_t alloc_size;
pool = ALLOC(sizeof(mp_pool_t));
CHECK_ALLOC(pool);
memset(pool, 0, sizeof(mp_pool_t));
/* First, we figure out how much space to allow per item. We'll want to
* use make sure we have enough for the overhead plus the item size. */
alloc_size = (size_t)(STRUCT_OFFSET(mp_allocated_t, u.mem) + item_size);
/* If the item_size is less than sizeof(next_free), we need to make
* the allocation bigger. */
if (alloc_size < sizeof(mp_allocated_t))
alloc_size = sizeof(mp_allocated_t);
/* If we're not an even multiple of ALIGNMENT, round up. */
if (alloc_size % ALIGNMENT) {
alloc_size = alloc_size + ALIGNMENT - (alloc_size % ALIGNMENT);
}
if (alloc_size < ALIGNMENT)
alloc_size = ALIGNMENT;
ASSERT((alloc_size % ALIGNMENT) == 0);
/* Now we figure out how many items fit in each chunk. We need to fit at
* least 2 items per chunk. No chunk can be more than MAX_CHUNK bytes long,
* or less than MIN_CHUNK. */
if (chunk_capacity > MAX_CHUNK)
chunk_capacity = MAX_CHUNK;
/* Try to be around a power of 2 in size, since that's what allocators like
* handing out. 512K-1 byte is a lot better than 512K+1 byte. */
chunk_capacity = (size_t) round_to_power_of_2(chunk_capacity);
while (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)
chunk_capacity *= 2;
if (chunk_capacity < MIN_CHUNK)
chunk_capacity = MIN_CHUNK;
pool->new_chunk_capacity = (chunk_capacity-CHUNK_OVERHEAD) / alloc_size;
pool->item_alloc_size = alloc_size;
log_debug(LD_MM, "Capacity is %lu, item size is %lu, alloc size is %lu",
(unsigned long)pool->new_chunk_capacity,
(unsigned long)pool->item_alloc_size,
(unsigned long)(pool->new_chunk_capacity*pool->item_alloc_size));
return pool;
}
/** If there are more than <b>n</b> empty chunks in <b>pool</b>, free the
2007-05-25 21:41:31 +02:00
* excess ones that have been empty for the longest. (If <b>n</b> is less
* than zero, free only empty chunks that were not used since the last
* call to mp_pool_clean(), leaving only -<b>n</b>.) */
void
mp_pool_clean(mp_pool_t *pool, int n)
{
mp_chunk_t *chunk, **first_to_free;
if (n < 0) {
/* As said in the documentation, "negative n" means "leave an additional
* -n chunks". So replace n with a positive number. */
n = pool->min_empty_chunks + (-n);
if (n < pool->n_empty_chunks)
pool->min_empty_chunks = n;
}
ASSERT(n>=0);
first_to_free = &pool->empty_chunks;
while (*first_to_free && n > 0) {
first_to_free = &(*first_to_free)->next;
--n;
}
if (!*first_to_free)
return;
chunk = *first_to_free;
while (chunk) {
mp_chunk_t *next = chunk->next;
chunk->magic = 0xdeadbeef;
FREE(chunk);
--pool->n_empty_chunks;
chunk = next;
}
*first_to_free = NULL;
}
/** Helper: Given a list of chunks, free all the chunks in the list. */
static void
destroy_chunks(mp_chunk_t *chunk)
{
mp_chunk_t *next;
while (chunk) {
chunk->magic = 0xd3adb33f;
next = chunk->next;
FREE(chunk);
chunk = next;
}
}
/** Free all space held in <b>pool</b> This makes all pointers returned from
* mp_pool_get(<b>pool</b>) invalid. */
void
mp_pool_destroy(mp_pool_t *pool)
{
destroy_chunks(pool->empty_chunks);
destroy_chunks(pool->used_chunks);
destroy_chunks(pool->full_chunks);
memset(pool, 0xe0, sizeof(mp_pool_t));
FREE(pool);
}
/** Helper: make sure that a given chunk list is not corrupt. */
static int
assert_chunks_ok(mp_pool_t *pool, mp_chunk_t *chunk, int empty, int full)
{
mp_allocated_t *allocated;
int n = 0;
if (chunk)
ASSERT(chunk->prev == NULL);
while (chunk) {
n++;
ASSERT(chunk->magic == MP_CHUNK_MAGIC);
ASSERT(chunk->pool == pool);
for (allocated = chunk->first_free; allocated;
allocated = allocated->u.next_free) {
ASSERT(allocated->in_chunk == chunk);
}
if (empty)
ASSERT(chunk->n_allocated == 0);
else if (full)
ASSERT(chunk->n_allocated == chunk->capacity);
else
ASSERT(chunk->n_allocated > 0 && chunk->n_allocated < chunk->capacity);
ASSERT(chunk->capacity == pool->new_chunk_capacity);
ASSERT(chunk->mem_size ==
pool->new_chunk_capacity * pool->item_alloc_size);
ASSERT(chunk->next_mem >= chunk->mem &&
chunk->next_mem <= chunk->mem + chunk->mem_size);
if (chunk->next)
ASSERT(chunk->next->prev == chunk);
chunk = chunk->next;
}
return n;
}
/** Fail with an assertion if <b>pool</b> is not internally consistent. */
void
mp_pool_assert_ok(mp_pool_t *pool)
{
int n_empty;
n_empty = assert_chunks_ok(pool, pool->empty_chunks, 1, 0);
assert_chunks_ok(pool, pool->full_chunks, 0, 1);
assert_chunks_ok(pool, pool->used_chunks, 0, 0);
ASSERT(pool->n_empty_chunks == n_empty);
}
#ifdef TOR
/** Dump information about <b>pool</b>'s memory usage to the Tor log at level
* <b>severity</b>. */
/*FFFF uses Tor logging functions. */
void
mp_pool_log_status(mp_pool_t *pool, int severity)
{
uint64_t bytes_used = 0;
uint64_t bytes_allocated = 0;
uint64_t bu = 0, ba = 0;
mp_chunk_t *chunk;
int n_full = 0, n_used = 0;
ASSERT(pool);
for (chunk = pool->empty_chunks; chunk; chunk = chunk->next) {
bytes_allocated += chunk->mem_size;
}
log_fn(severity, LD_MM, U64_FORMAT" bytes in %d empty chunks",
U64_PRINTF_ARG(bytes_used), pool->n_empty_chunks);
for (chunk = pool->used_chunks; chunk; chunk = chunk->next) {
++n_used;
bu += chunk->n_allocated * pool->item_alloc_size;
ba += chunk->mem_size;
}
log_fn(severity, LD_MM, U64_FORMAT"/"U64_FORMAT
" bytes in %d partially full chunks",
U64_PRINTF_ARG(bu), U64_PRINTF_ARG(ba), n_used);
bytes_used += bu;
bytes_allocated += ba;
bu = ba = 0;
for (chunk = pool->full_chunks; chunk; chunk = chunk->next) {
++n_full;
bu += chunk->n_allocated * pool->item_alloc_size;
ba += chunk->mem_size;
}
log_fn(severity, LD_MM, U64_FORMAT"/"U64_FORMAT
" bytes in %d full chunks",
U64_PRINTF_ARG(bu), U64_PRINTF_ARG(ba), n_full);
bytes_used += bu;
bytes_allocated += ba;
log_fn(severity, LD_MM, "Total: "U64_FORMAT"/"U64_FORMAT" bytes allocated "
"for cell pools are full.",
U64_PRINTF_ARG(bytes_used), U64_PRINTF_ARG(bytes_allocated));
}
#endif