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r12338@catbus: nickm | 2007-04-10 20:29:05 -0400

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Document memory pool implementation, and tweak it even mor.  See? Programming is fun.


svn:r9940
This commit is contained in:
Nick Mathewson 2007-04-11 00:30:34 +00:00
parent 28de06b8e6
commit 51e4b8d706
6 changed files with 222 additions and 85 deletions
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2
ChangeLog
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@ -6,6 +6,8 @@ Changes in version 0.2.0.1-alpha - 2007-??-??
queue for each circuit. This lets us use less slack memory, and
will eventually let us be smarter about prioritizing different kinds
of traffic.
- Allocate cells in memory pools better speed and memory efficiency,
especially on platforms where malloc() is inefficient.
- Stop reading on edge connections when their corresponding circuit
buffers are full; start again as the circuits empty out.

7
doc/TODO
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@ -75,7 +75,12 @@ Things we'd like to do in 0.2.0.x:
[No need to do this: the edge-connection choking will already take
care of this a bit, and rewriting the 'bridged connection' code
to not use socketpairs will give us even more control.]
- Do we switch to arena-allocation for cells?
. Do we switch to pool-allocation for cells?
o Implement pool-allocation
o Have Tor use it for packed cells.
o Document it.
- Do something smart with freeing unused chunks.
- Benchmark pool-allocation vs straightforward malloc.
- Can we stop doing so many memcpys on cells?
o Also, only package data from exitconns when there is space on the
target OR conn's outbuf? or when the circuit is not too full.

247
src/common/mempool.c
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@ -1,6 +1,6 @@
/* Copyright 2007 Nick Mathewson */
/* See LICENSE for licensing information */
/* $Id: /tor/trunk/src/common/util.c 12153 2007-03-12T03:11:12.797278Z nickm $ */
/* $Id$ */
#include <stdlib.h>
#include <string.h>
@ -8,10 +8,48 @@
#include "mempool.h"
/* OVERVIEW:
* DOCDOC
*/
/* DRAWBACKS:
*
* 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
* and coalescing strategeis 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,
* since that's the one I looked at longest ago) 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
@ -24,12 +62,6 @@
* - probably, chunks should always be a power of 2.
*/
/* NOTES:
* - The algorithm is similar to the one used by Python, but assumes that
* we'll know in advance which objects we want to pool, and doesn't
* try to handle a zillion objects of weird different sizes.
*/
#if 1
/* Tor dependencies */
#include "orconfig.h"
@ -39,8 +71,12 @@
#define ALLOC(x) tor_malloc(x)
#define FREE(x) tor_free(x)
#define ASSERT(x) tor_assert(x)
#undef ALLOC_CAN_RETURN_NULL
/* 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)
@ -49,63 +85,90 @@
#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 */
/** DOCDOC */
/** 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 *
/** DOCDOC */
#define ALIGNMENT sizeof(void*)
/** DOCDOC */
/** 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))
/** DOCDOC */
/** 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;
/** DOCDOC */
/** 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;
};
};
/** DOCDOC */
struct mp_chunk_t {
unsigned long magic;
mp_chunk_t *next;
mp_chunk_t *prev;
mp_pool_t *pool;
mp_allocated_t *first_free;
int n_allocated;
int capacity;
size_t mem_size;
char *next_mem;
char mem[1];
};
/** DOCDOC */
/** 'Magic' value used to detect memory corruption. */
#define MP_CHUNK_MAGIC 0x09870123
/** DOCDOC */
/** 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. */
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;
int n_allocated; /**< Number of currently allocated items in this chunk */
int capacity; /**< Largest 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)
/** DOCDOC */
/** Given a pointer to a mp_allocated_t, return a pointer to the memory
* item it holds. */
#define A2M(a) (&(a)->mem[0])
/** DOCDOC */
/** 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, mem) )
/* INVARIANT: every chunk can hold 2 or more items. */
#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
/** DOCDOC */
/** 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;
@ -115,29 +178,44 @@ mp_chunk_new(mp_pool_t *pool)
return chunk;
}
/** DOCDOC */
/** 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) {
/* Put the most recently emptied chunk on the used list. */
/* 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;
} else {
/* Allocate a new chunk and add it to the used list. */
/* 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;
@ -148,40 +226,52 @@ mp_pool_get(mp_pool_t *pool)
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->next_free;
allocated->next_free = NULL; /* debugging */
allocated->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->next_free = NULL; /* For debugging; not really needed. */
}
++chunk->n_allocated;
if (PREDICT_UNLIKELY(chunk->n_allocated == chunk->capacity)) {
/* This is now a full chunk. */
/* 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);
}
/** DOCDOC */
/** Return an allocated memory item to its memory pool. */
void
mp_pool_release(void *_item)
mp_pool_release(void *item)
{
mp_allocated_t *allocated = (void*) M2A(_item);
mp_allocated_t *allocated = (void*) M2A(item);
mp_chunk_t *chunk = allocated->in_chunk;
ASSERT(chunk);
@ -194,7 +284,7 @@ mp_pool_release(void *_item)
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 full */
/* unlink from the full list */
if (chunk->prev)
chunk->prev->next = chunk->next;
if (chunk->next)
@ -202,7 +292,7 @@ mp_pool_release(void *_item)
if (chunk == pool->full_chunks)
pool->full_chunks = chunk->next;
/* link to used */
/* link to the used list. */
chunk->next = pool->used_chunks;
chunk->prev = NULL;
if (chunk->next)
@ -211,7 +301,8 @@ mp_pool_release(void *_item)
} 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 used */
/* Unlink from the used list */
if (chunk->prev)
chunk->prev->next = chunk->next;
if (chunk->next)
@ -219,23 +310,26 @@ mp_pool_release(void *_item)
if (chunk == pool->used_chunks)
pool->used_chunks = chunk->next;
/* link to empty */
/* 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 guts to defragment this 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;
}
/** DOCDOC */
/** Allocate a new memory pool to hold items of size <b>item_size</b>. We'll
* try to fit about <b>chunk_capacity</b> items in each chunk. */
mp_pool_t *
mp_pool_new(size_t item_size, size_t chunk_capacity)
{
@ -243,29 +337,35 @@ mp_pool_new(size_t item_size, size_t chunk_capacity)
size_t alloc_size;
pool = ALLOC(sizeof(mp_pool_t));
CHECK_ALLOC(pool);
memset(pool, 0, sizeof(mp_pool_t));
/* First, minimal size with overhead. */
/* 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 = STRUCT_OFFSET(mp_allocated_t, 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);
/* Then, round up to alignment. */
/* 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. */
/* XXXX020 Try a bit harder here: we want to be a bit less than a power of
2, not a bit over. */
if (chunk_capacity > MAX_CHUNK)
chunk_capacity = MAX_CHUNK;
if (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)
chunk_capacity = alloc_size * 2 + CHUNK_OVERHEAD;
if (chunk_capacity < MIN_CHUNK) /* Guess system page size. */
if (chunk_capacity < MIN_CHUNK)
chunk_capacity = MIN_CHUNK;
pool->new_chunk_capacity = (chunk_capacity-CHUNK_OVERHEAD) / alloc_size;
@ -274,23 +374,33 @@ mp_pool_new(size_t item_size, size_t chunk_capacity)
return pool;
}
/** DOCDOC */
/** If there are more than <b>n</b> empty chunks in <b>pool</b>, free the
* exces ones that have been empty for the longest. */
void
mp_pool_clean(mp_pool_t *pool)
mp_pool_clean(mp_pool_t *pool, int n)
{
if (pool->empty_chunks) {
mp_chunk_t *next, *chunk = pool->empty_chunks->next;
mp_chunk_t *chunk, **first_to_free;
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) {
next = chunk->next;
mp_chunk_t *next = chunk->next;
chunk->magic = 0xdeadbeef;
FREE(chunk);
--pool->n_empty_chunks;
chunk = next;
}
pool->empty_chunks->next = NULL;
pool->n_empty_chunks = 1;
}
*first_to_free = NULL;
}
/** DOCDOC */
/** Helper: Given a list of chunks, free all the chunks in the list. */
static void
destroy_chunks(mp_chunk_t *chunk)
{
@ -303,7 +413,8 @@ destroy_chunks(mp_chunk_t *chunk)
}
}
/** DOCDOC */
/** 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)
{
@ -314,6 +425,7 @@ mp_pool_destroy(mp_pool_t *pool)
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)
{
@ -353,6 +465,7 @@ assert_chunks_ok(mp_pool_t *pool, mp_chunk_t *chunk, int empty, int full)
return n;
}
/** Fail with an assertion if <b>pool</b> is not internally consistent. */
void
mp_pool_assert_ok(mp_pool_t *pool)
{

27
src/common/mempool.h
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@ -1,6 +1,6 @@
/* Copyright 2007 Nick Mathewson */
/* See LICENSE for licensing information */
/* $Id: /tor/trunk/src/common/util.c 12153 2007-03-12T03:11:12.797278Z nickm $ */
/* $Id$ */
/**
* \file util.h
@ -10,25 +10,38 @@
#ifndef MEMPOOL_H
#define MEMPOOL_H
/** A memory pool is a context in which a large number of fixed-sized
* objects can be allocated efficiently. See mempool.c for implementation
* details. */
typedef struct mp_pool_t mp_pool_t;
void *mp_pool_get(mp_pool_t *pool);
void mp_pool_release(void *item);
mp_pool_t *mp_pool_new(size_t item_size, unsigned int n_per_chunk);
void mp_pool_clean(mp_pool_t *pool);
void mp_pool_clean(mp_pool_t *pool, int n);
void mp_pool_destroy(mp_pool_t *pool);
void mp_pool_assert_ok(mp_pool_t *pool);
#ifdef MEMPOOL_PRIVATE
typedef struct mp_chunk_t mp_chunk_t;
/* These declarations are only used by mempool.c and test.c */
/** DOCDOC */
struct mp_pool_t {
mp_chunk_t *empty_chunks;
mp_chunk_t *used_chunks;
mp_chunk_t *full_chunks;
/** Doubly-linked list of chunks in which no items have been allocated.
* The front of the list is the most recently emptied chunk. */
struct mp_chunk_t *empty_chunks;
/** Doubly-linked list of chunks in which some items have been allocated,
* but which are not yet full. The front of the list is the chunk that has
* most recently been modified. */
struct mp_chunk_t *used_chunks;
/** Doubly-linked list of chunks in which no more items can be allocated.
* The front of the list is the chunk that has most recently become full. */
struct mp_chunk_t *full_chunks;
/** Length of <b>empty_chunks</b>. */
int n_empty_chunks;
/** Size of each chunk (in items). */
int new_chunk_capacity;
/** Size to allocate for each item, including overhead and alignment
* padding. */
size_t item_alloc_size;
};
#endif

12
src/or/relay.c
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@ -1479,8 +1479,8 @@ circuit_consider_sending_sendme(circuit_t *circ, crypt_path_t *layer_hint)
#endif
#ifdef ENABLE_CELL_POOL
static mp_pool_t *cell_pool;
/* DOCDOC */
static mp_pool_t *cell_pool = NULL;
/** Allocate structures to hold cells. */
void
init_cell_pool(void)
{
@ -1488,7 +1488,7 @@ init_cell_pool(void)
cell_pool = mp_pool_new(sizeof(packed_cell_t), 64);
}
/* DOCDOC */
/** Free all storage used to hold cells. */
void
free_cell_pool(void)
{
@ -1497,20 +1497,22 @@ free_cell_pool(void)
cell_pool = NULL;
}
/** Release storage held by <b>cell</b> */
/** Release storage held by <b>cell</b>. */
static INLINE void
packed_cell_free(packed_cell_t *cell)
{
mp_pool_release(cell);
}
/* DOCDOC */
/** Allocate and return a new packed_cell_t. */
static INLINE packed_cell_t *
packed_cell_alloc(void)
{
return mp_pool_get(cell_pool);
}
#else
/* ENABLE_CELL_POOL isn't defined: here are some stubs to use tor_malloc()
* and tor_free() instead. */
void
init_cell_pool(void)
{

4
src/or/test.c
View File

@ -2142,13 +2142,15 @@ test_mempool(void)
//mp_pool_assert_ok(pool);
}
if (crypto_rand_int(777)==0)
mp_pool_clean(pool);
mp_pool_clean(pool, 2);
if (i % 777)
mp_pool_assert_ok(pool);
}
SMARTLIST_FOREACH(allocated, void *, m, mp_pool_release(m));
mp_pool_assert_ok(pool);
mp_pool_clean(pool, 0);
mp_pool_assert_ok(pool);
mp_pool_destroy(pool);
smartlist_free(allocated);
}