/Objects/obmalloc.c
C | 1765 lines | 854 code | 178 blank | 733 comment | 200 complexity | 25e3cb94ae75a45a8cdcc27df47330d6 MD5 | raw file
Possible License(s): 0BSD, BSD-3-Clause
- #include "Python.h"
- #ifdef WITH_PYMALLOC
- /* An object allocator for Python.
- Here is an introduction to the layers of the Python memory architecture,
- showing where the object allocator is actually used (layer +2), It is
- called for every object allocation and deallocation (PyObject_New/Del),
- unless the object-specific allocators implement a proprietary allocation
- scheme (ex.: ints use a simple free list). This is also the place where
- the cyclic garbage collector operates selectively on container objects.
- Object-specific allocators
- _____ ______ ______ ________
- [ int ] [ dict ] [ list ] ... [ string ] Python core |
- +3 | <----- Object-specific memory -----> | <-- Non-object memory --> |
- _______________________________ | |
- [ Python's object allocator ] | |
- +2 | ####### Object memory ####### | <------ Internal buffers ------> |
- ______________________________________________________________ |
- [ Python's raw memory allocator (PyMem_ API) ] |
- +1 | <----- Python memory (under PyMem manager's control) ------> | |
- __________________________________________________________________
- [ Underlying general-purpose allocator (ex: C library malloc) ]
- 0 | <------ Virtual memory allocated for the python process -------> |
- =========================================================================
- _______________________________________________________________________
- [ OS-specific Virtual Memory Manager (VMM) ]
- -1 | <--- Kernel dynamic storage allocation & management (page-based) ---> |
- __________________________________ __________________________________
- [ ] [ ]
- -2 | <-- Physical memory: ROM/RAM --> | | <-- Secondary storage (swap) --> |
- */
- /*==========================================================================*/
- /* A fast, special-purpose memory allocator for small blocks, to be used
- on top of a general-purpose malloc -- heavily based on previous art. */
- /* Vladimir Marangozov -- August 2000 */
- /*
- * "Memory management is where the rubber meets the road -- if we do the wrong
- * thing at any level, the results will not be good. And if we don't make the
- * levels work well together, we are in serious trouble." (1)
- *
- * (1) Paul R. Wilson, Mark S. Johnstone, Michael Neely, and David Boles,
- * "Dynamic Storage Allocation: A Survey and Critical Review",
- * in Proc. 1995 Int'l. Workshop on Memory Management, September 1995.
- */
- /* #undef WITH_MEMORY_LIMITS */ /* disable mem limit checks */
- /*==========================================================================*/
- /*
- * Allocation strategy abstract:
- *
- * For small requests, the allocator sub-allocates <Big> blocks of memory.
- * Requests greater than 256 bytes are routed to the system's allocator.
- *
- * Small requests are grouped in size classes spaced 8 bytes apart, due
- * to the required valid alignment of the returned address. Requests of
- * a particular size are serviced from memory pools of 4K (one VMM page).
- * Pools are fragmented on demand and contain free lists of blocks of one
- * particular size class. In other words, there is a fixed-size allocator
- * for each size class. Free pools are shared by the different allocators
- * thus minimizing the space reserved for a particular size class.
- *
- * This allocation strategy is a variant of what is known as "simple
- * segregated storage based on array of free lists". The main drawback of
- * simple segregated storage is that we might end up with lot of reserved
- * memory for the different free lists, which degenerate in time. To avoid
- * this, we partition each free list in pools and we share dynamically the
- * reserved space between all free lists. This technique is quite efficient
- * for memory intensive programs which allocate mainly small-sized blocks.
- *
- * For small requests we have the following table:
- *
- * Request in bytes Size of allocated block Size class idx
- * ----------------------------------------------------------------
- * 1-8 8 0
- * 9-16 16 1
- * 17-24 24 2
- * 25-32 32 3
- * 33-40 40 4
- * 41-48 48 5
- * 49-56 56 6
- * 57-64 64 7
- * 65-72 72 8
- * ... ... ...
- * 241-248 248 30
- * 249-256 256 31
- *
- * 0, 257 and up: routed to the underlying allocator.
- */
- /*==========================================================================*/
- /*
- * -- Main tunable settings section --
- */
- /*
- * Alignment of addresses returned to the user. 8-bytes alignment works
- * on most current architectures (with 32-bit or 64-bit address busses).
- * The alignment value is also used for grouping small requests in size
- * classes spaced ALIGNMENT bytes apart.
- *
- * You shouldn't change this unless you know what you are doing.
- */
- #define ALIGNMENT 8 /* must be 2^N */
- #define ALIGNMENT_SHIFT 3
- #define ALIGNMENT_MASK (ALIGNMENT - 1)
- /* Return the number of bytes in size class I, as a uint. */
- #define INDEX2SIZE(I) (((uint)(I) + 1) << ALIGNMENT_SHIFT)
- /*
- * Max size threshold below which malloc requests are considered to be
- * small enough in order to use preallocated memory pools. You can tune
- * this value according to your application behaviour and memory needs.
- *
- * The following invariants must hold:
- * 1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
- * 2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
- *
- * Although not required, for better performance and space efficiency,
- * it is recommended that SMALL_REQUEST_THRESHOLD is set to a power of 2.
- */
- #define SMALL_REQUEST_THRESHOLD 256
- #define NB_SMALL_SIZE_CLASSES (SMALL_REQUEST_THRESHOLD / ALIGNMENT)
- /*
- * The system's VMM page size can be obtained on most unices with a
- * getpagesize() call or deduced from various header files. To make
- * things simpler, we assume that it is 4K, which is OK for most systems.
- * It is probably better if this is the native page size, but it doesn't
- * have to be. In theory, if SYSTEM_PAGE_SIZE is larger than the native page
- * size, then `POOL_ADDR(p)->arenaindex' could rarely cause a segmentation
- * violation fault. 4K is apparently OK for all the platforms that python
- * currently targets.
- */
- #define SYSTEM_PAGE_SIZE (4 * 1024)
- #define SYSTEM_PAGE_SIZE_MASK (SYSTEM_PAGE_SIZE - 1)
- /*
- * Maximum amount of memory managed by the allocator for small requests.
- */
- #ifdef WITH_MEMORY_LIMITS
- #ifndef SMALL_MEMORY_LIMIT
- #define SMALL_MEMORY_LIMIT (64 * 1024 * 1024) /* 64 MB -- more? */
- #endif
- #endif
- /*
- * The allocator sub-allocates <Big> blocks of memory (called arenas) aligned
- * on a page boundary. This is a reserved virtual address space for the
- * current process (obtained through a malloc call). In no way this means
- * that the memory arenas will be used entirely. A malloc(<Big>) is usually
- * an address range reservation for <Big> bytes, unless all pages within this
- * space are referenced subsequently. So malloc'ing big blocks and not using
- * them does not mean "wasting memory". It's an addressable range wastage...
- *
- * Therefore, allocating arenas with malloc is not optimal, because there is
- * some address space wastage, but this is the most portable way to request
- * memory from the system across various platforms.
- */
- #define ARENA_SIZE (256 << 10) /* 256KB */
- #ifdef WITH_MEMORY_LIMITS
- #define MAX_ARENAS (SMALL_MEMORY_LIMIT / ARENA_SIZE)
- #endif
- /*
- * Size of the pools used for small blocks. Should be a power of 2,
- * between 1K and SYSTEM_PAGE_SIZE, that is: 1k, 2k, 4k.
- */
- #define POOL_SIZE SYSTEM_PAGE_SIZE /* must be 2^N */
- #define POOL_SIZE_MASK SYSTEM_PAGE_SIZE_MASK
- /*
- * -- End of tunable settings section --
- */
- /*==========================================================================*/
- /*
- * Locking
- *
- * To reduce lock contention, it would probably be better to refine the
- * crude function locking with per size class locking. I'm not positive
- * however, whether it's worth switching to such locking policy because
- * of the performance penalty it might introduce.
- *
- * The following macros describe the simplest (should also be the fastest)
- * lock object on a particular platform and the init/fini/lock/unlock
- * operations on it. The locks defined here are not expected to be recursive
- * because it is assumed that they will always be called in the order:
- * INIT, [LOCK, UNLOCK]*, FINI.
- */
- /*
- * Python's threads are serialized, so object malloc locking is disabled.
- */
- #define SIMPLELOCK_DECL(lock) /* simple lock declaration */
- #define SIMPLELOCK_INIT(lock) /* allocate (if needed) and initialize */
- #define SIMPLELOCK_FINI(lock) /* free/destroy an existing lock */
- #define SIMPLELOCK_LOCK(lock) /* acquire released lock */
- #define SIMPLELOCK_UNLOCK(lock) /* release acquired lock */
- /*
- * Basic types
- * I don't care if these are defined in <sys/types.h> or elsewhere. Axiom.
- */
- #undef uchar
- #define uchar unsigned char /* assuming == 8 bits */
- #undef uint
- #define uint unsigned int /* assuming >= 16 bits */
- #undef ulong
- #define ulong unsigned long /* assuming >= 32 bits */
- #undef uptr
- #define uptr Py_uintptr_t
- /* When you say memory, my mind reasons in terms of (pointers to) blocks */
- typedef uchar block;
- /* Pool for small blocks. */
- struct pool_header {
- union { block *_padding;
- uint count; } ref; /* number of allocated blocks */
- block *freeblock; /* pool's free list head */
- struct pool_header *nextpool; /* next pool of this size class */
- struct pool_header *prevpool; /* previous pool "" */
- uint arenaindex; /* index into arenas of base adr */
- uint szidx; /* block size class index */
- uint nextoffset; /* bytes to virgin block */
- uint maxnextoffset; /* largest valid nextoffset */
- };
- typedef struct pool_header *poolp;
- /* Record keeping for arenas. */
- struct arena_object {
- /* The address of the arena, as returned by malloc. Note that 0
- * will never be returned by a successful malloc, and is used
- * here to mark an arena_object that doesn't correspond to an
- * allocated arena.
- */
- uptr address;
- /* Pool-aligned pointer to the next pool to be carved off. */
- block* pool_address;
- /* The number of available pools in the arena: free pools + never-
- * allocated pools.
- */
- uint nfreepools;
- /* The total number of pools in the arena, whether or not available. */
- uint ntotalpools;
- /* Singly-linked list of available pools. */
- struct pool_header* freepools;
- /* Whenever this arena_object is not associated with an allocated
- * arena, the nextarena member is used to link all unassociated
- * arena_objects in the singly-linked `unused_arena_objects` list.
- * The prevarena member is unused in this case.
- *
- * When this arena_object is associated with an allocated arena
- * with at least one available pool, both members are used in the
- * doubly-linked `usable_arenas` list, which is maintained in
- * increasing order of `nfreepools` values.
- *
- * Else this arena_object is associated with an allocated arena
- * all of whose pools are in use. `nextarena` and `prevarena`
- * are both meaningless in this case.
- */
- struct arena_object* nextarena;
- struct arena_object* prevarena;
- };
- #undef ROUNDUP
- #define ROUNDUP(x) (((x) + ALIGNMENT_MASK) & ~ALIGNMENT_MASK)
- #define POOL_OVERHEAD ROUNDUP(sizeof(struct pool_header))
- #define DUMMY_SIZE_IDX 0xffff /* size class of newly cached pools */
- /* Round pointer P down to the closest pool-aligned address <= P, as a poolp */
- #define POOL_ADDR(P) ((poolp)((uptr)(P) & ~(uptr)POOL_SIZE_MASK))
- /* Return total number of blocks in pool of size index I, as a uint. */
- #define NUMBLOCKS(I) ((uint)(POOL_SIZE - POOL_OVERHEAD) / INDEX2SIZE(I))
- /*==========================================================================*/
- /*
- * This malloc lock
- */
- SIMPLELOCK_DECL(_malloc_lock)
- #define LOCK() SIMPLELOCK_LOCK(_malloc_lock)
- #define UNLOCK() SIMPLELOCK_UNLOCK(_malloc_lock)
- #define LOCK_INIT() SIMPLELOCK_INIT(_malloc_lock)
- #define LOCK_FINI() SIMPLELOCK_FINI(_malloc_lock)
- /*
- * Pool table -- headed, circular, doubly-linked lists of partially used pools.
- This is involved. For an index i, usedpools[i+i] is the header for a list of
- all partially used pools holding small blocks with "size class idx" i. So
- usedpools[0] corresponds to blocks of size 8, usedpools[2] to blocks of size
- 16, and so on: index 2*i <-> blocks of size (i+1)<<ALIGNMENT_SHIFT.
- Pools are carved off an arena's highwater mark (an arena_object's pool_address
- member) as needed. Once carved off, a pool is in one of three states forever
- after:
- used == partially used, neither empty nor full
- At least one block in the pool is currently allocated, and at least one
- block in the pool is not currently allocated (note this implies a pool
- has room for at least two blocks).
- This is a pool's initial state, as a pool is created only when malloc
- needs space.
- The pool holds blocks of a fixed size, and is in the circular list headed
- at usedpools[i] (see above). It's linked to the other used pools of the
- same size class via the pool_header's nextpool and prevpool members.
- If all but one block is currently allocated, a malloc can cause a
- transition to the full state. If all but one block is not currently
- allocated, a free can cause a transition to the empty state.
- full == all the pool's blocks are currently allocated
- On transition to full, a pool is unlinked from its usedpools[] list.
- It's not linked to from anything then anymore, and its nextpool and
- prevpool members are meaningless until it transitions back to used.
- A free of a block in a full pool puts the pool back in the used state.
- Then it's linked in at the front of the appropriate usedpools[] list, so
- that the next allocation for its size class will reuse the freed block.
- empty == all the pool's blocks are currently available for allocation
- On transition to empty, a pool is unlinked from its usedpools[] list,
- and linked to the front of its arena_object's singly-linked freepools list,
- via its nextpool member. The prevpool member has no meaning in this case.
- Empty pools have no inherent size class: the next time a malloc finds
- an empty list in usedpools[], it takes the first pool off of freepools.
- If the size class needed happens to be the same as the size class the pool
- last had, some pool initialization can be skipped.
- Block Management
- Blocks within pools are again carved out as needed. pool->freeblock points to
- the start of a singly-linked list of free blocks within the pool. When a
- block is freed, it's inserted at the front of its pool's freeblock list. Note
- that the available blocks in a pool are *not* linked all together when a pool
- is initialized. Instead only "the first two" (lowest addresses) blocks are
- set up, returning the first such block, and setting pool->freeblock to a
- one-block list holding the second such block. This is consistent with that
- pymalloc strives at all levels (arena, pool, and block) never to touch a piece
- of memory until it's actually needed.
- So long as a pool is in the used state, we're certain there *is* a block
- available for allocating, and pool->freeblock is not NULL. If pool->freeblock
- points to the end of the free list before we've carved the entire pool into
- blocks, that means we simply haven't yet gotten to one of the higher-address
- blocks. The offset from the pool_header to the start of "the next" virgin
- block is stored in the pool_header nextoffset member, and the largest value
- of nextoffset that makes sense is stored in the maxnextoffset member when a
- pool is initialized. All the blocks in a pool have been passed out at least
- once when and only when nextoffset > maxnextoffset.
- Major obscurity: While the usedpools vector is declared to have poolp
- entries, it doesn't really. It really contains two pointers per (conceptual)
- poolp entry, the nextpool and prevpool members of a pool_header. The
- excruciating initialization code below fools C so that
- usedpool[i+i]
- "acts like" a genuine poolp, but only so long as you only reference its
- nextpool and prevpool members. The "- 2*sizeof(block *)" gibberish is
- compensating for that a pool_header's nextpool and prevpool members
- immediately follow a pool_header's first two members:
- union { block *_padding;
- uint count; } ref;
- block *freeblock;
- each of which consume sizeof(block *) bytes. So what usedpools[i+i] really
- contains is a fudged-up pointer p such that *if* C believes it's a poolp
- pointer, then p->nextpool and p->prevpool are both p (meaning that the headed
- circular list is empty).
- It's unclear why the usedpools setup is so convoluted. It could be to
- minimize the amount of cache required to hold this heavily-referenced table
- (which only *needs* the two interpool pointer members of a pool_header). OTOH,
- referencing code has to remember to "double the index" and doing so isn't
- free, usedpools[0] isn't a strictly legal pointer, and we're crucially relying
- on that C doesn't insert any padding anywhere in a pool_header at or before
- the prevpool member.
- **************************************************************************** */
- #define PTA(x) ((poolp )((uchar *)&(usedpools[2*(x)]) - 2*sizeof(block *)))
- #define PT(x) PTA(x), PTA(x)
- static poolp usedpools[2 * ((NB_SMALL_SIZE_CLASSES + 7) / 8) * 8] = {
- PT(0), PT(1), PT(2), PT(3), PT(4), PT(5), PT(6), PT(7)
- #if NB_SMALL_SIZE_CLASSES > 8
- , PT(8), PT(9), PT(10), PT(11), PT(12), PT(13), PT(14), PT(15)
- #if NB_SMALL_SIZE_CLASSES > 16
- , PT(16), PT(17), PT(18), PT(19), PT(20), PT(21), PT(22), PT(23)
- #if NB_SMALL_SIZE_CLASSES > 24
- , PT(24), PT(25), PT(26), PT(27), PT(28), PT(29), PT(30), PT(31)
- #if NB_SMALL_SIZE_CLASSES > 32
- , PT(32), PT(33), PT(34), PT(35), PT(36), PT(37), PT(38), PT(39)
- #if NB_SMALL_SIZE_CLASSES > 40
- , PT(40), PT(41), PT(42), PT(43), PT(44), PT(45), PT(46), PT(47)
- #if NB_SMALL_SIZE_CLASSES > 48
- , PT(48), PT(49), PT(50), PT(51), PT(52), PT(53), PT(54), PT(55)
- #if NB_SMALL_SIZE_CLASSES > 56
- , PT(56), PT(57), PT(58), PT(59), PT(60), PT(61), PT(62), PT(63)
- #endif /* NB_SMALL_SIZE_CLASSES > 56 */
- #endif /* NB_SMALL_SIZE_CLASSES > 48 */
- #endif /* NB_SMALL_SIZE_CLASSES > 40 */
- #endif /* NB_SMALL_SIZE_CLASSES > 32 */
- #endif /* NB_SMALL_SIZE_CLASSES > 24 */
- #endif /* NB_SMALL_SIZE_CLASSES > 16 */
- #endif /* NB_SMALL_SIZE_CLASSES > 8 */
- };
- /*==========================================================================
- Arena management.
- `arenas` is a vector of arena_objects. It contains maxarenas entries, some of
- which may not be currently used (== they're arena_objects that aren't
- currently associated with an allocated arena). Note that arenas proper are
- separately malloc'ed.
- Prior to Python 2.5, arenas were never free()'ed. Starting with Python 2.5,
- we do try to free() arenas, and use some mild heuristic strategies to increase
- the likelihood that arenas eventually can be freed.
- unused_arena_objects
- This is a singly-linked list of the arena_objects that are currently not
- being used (no arena is associated with them). Objects are taken off the
- head of the list in new_arena(), and are pushed on the head of the list in
- PyObject_Free() when the arena is empty. Key invariant: an arena_object
- is on this list if and only if its .address member is 0.
- usable_arenas
- This is a doubly-linked list of the arena_objects associated with arenas
- that have pools available. These pools are either waiting to be reused,
- or have not been used before. The list is sorted to have the most-
- allocated arenas first (ascending order based on the nfreepools member).
- This means that the next allocation will come from a heavily used arena,
- which gives the nearly empty arenas a chance to be returned to the system.
- In my unscientific tests this dramatically improved the number of arenas
- that could be freed.
- Note that an arena_object associated with an arena all of whose pools are
- currently in use isn't on either list.
- */
- /* Array of objects used to track chunks of memory (arenas). */
- static struct arena_object* arenas = NULL;
- /* Number of slots currently allocated in the `arenas` vector. */
- static uint maxarenas = 0;
- /* The head of the singly-linked, NULL-terminated list of available
- * arena_objects.
- */
- static struct arena_object* unused_arena_objects = NULL;
- /* The head of the doubly-linked, NULL-terminated at each end, list of
- * arena_objects associated with arenas that have pools available.
- */
- static struct arena_object* usable_arenas = NULL;
- /* How many arena_objects do we initially allocate?
- * 16 = can allocate 16 arenas = 16 * ARENA_SIZE = 4MB before growing the
- * `arenas` vector.
- */
- #define INITIAL_ARENA_OBJECTS 16
- /* Number of arenas allocated that haven't been free()'d. */
- static size_t narenas_currently_allocated = 0;
- #ifdef PYMALLOC_DEBUG
- /* Total number of times malloc() called to allocate an arena. */
- static size_t ntimes_arena_allocated = 0;
- /* High water mark (max value ever seen) for narenas_currently_allocated. */
- static size_t narenas_highwater = 0;
- #endif
- /* Allocate a new arena. If we run out of memory, return NULL. Else
- * allocate a new arena, and return the address of an arena_object
- * describing the new arena. It's expected that the caller will set
- * `usable_arenas` to the return value.
- */
- static struct arena_object*
- new_arena(void)
- {
- struct arena_object* arenaobj;
- uint excess; /* number of bytes above pool alignment */
- #ifdef PYMALLOC_DEBUG
- if (Py_GETENV("PYTHONMALLOCSTATS"))
- _PyObject_DebugMallocStats();
- #endif
- if (unused_arena_objects == NULL) {
- uint i;
- uint numarenas;
- size_t nbytes;
- /* Double the number of arena objects on each allocation.
- * Note that it's possible for `numarenas` to overflow.
- */
- numarenas = maxarenas ? maxarenas << 1 : INITIAL_ARENA_OBJECTS;
- if (numarenas <= maxarenas)
- return NULL; /* overflow */
- #if SIZEOF_SIZE_T <= SIZEOF_INT
- if (numarenas > PY_SIZE_MAX / sizeof(*arenas))
- return NULL; /* overflow */
- #endif
- nbytes = numarenas * sizeof(*arenas);
- arenaobj = (struct arena_object *)realloc(arenas, nbytes);
- if (arenaobj == NULL)
- return NULL;
- arenas = arenaobj;
- /* We might need to fix pointers that were copied. However,
- * new_arena only gets called when all the pages in the
- * previous arenas are full. Thus, there are *no* pointers
- * into the old array. Thus, we don't have to worry about
- * invalid pointers. Just to be sure, some asserts:
- */
- assert(usable_arenas == NULL);
- assert(unused_arena_objects == NULL);
- /* Put the new arenas on the unused_arena_objects list. */
- for (i = maxarenas; i < numarenas; ++i) {
- arenas[i].address = 0; /* mark as unassociated */
- arenas[i].nextarena = i < numarenas - 1 ?
- &arenas[i+1] : NULL;
- }
- /* Update globals. */
- unused_arena_objects = &arenas[maxarenas];
- maxarenas = numarenas;
- }
- /* Take the next available arena object off the head of the list. */
- assert(unused_arena_objects != NULL);
- arenaobj = unused_arena_objects;
- unused_arena_objects = arenaobj->nextarena;
- assert(arenaobj->address == 0);
- arenaobj->address = (uptr)malloc(ARENA_SIZE);
- if (arenaobj->address == 0) {
- /* The allocation failed: return NULL after putting the
- * arenaobj back.
- */
- arenaobj->nextarena = unused_arena_objects;
- unused_arena_objects = arenaobj;
- return NULL;
- }
- ++narenas_currently_allocated;
- #ifdef PYMALLOC_DEBUG
- ++ntimes_arena_allocated;
- if (narenas_currently_allocated > narenas_highwater)
- narenas_highwater = narenas_currently_allocated;
- #endif
- arenaobj->freepools = NULL;
- /* pool_address <- first pool-aligned address in the arena
- nfreepools <- number of whole pools that fit after alignment */
- arenaobj->pool_address = (block*)arenaobj->address;
- arenaobj->nfreepools = ARENA_SIZE / POOL_SIZE;
- assert(POOL_SIZE * arenaobj->nfreepools == ARENA_SIZE);
- excess = (uint)(arenaobj->address & POOL_SIZE_MASK);
- if (excess != 0) {
- --arenaobj->nfreepools;
- arenaobj->pool_address += POOL_SIZE - excess;
- }
- arenaobj->ntotalpools = arenaobj->nfreepools;
- return arenaobj;
- }
- /*
- Py_ADDRESS_IN_RANGE(P, POOL)
- Return true if and only if P is an address that was allocated by pymalloc.
- POOL must be the pool address associated with P, i.e., POOL = POOL_ADDR(P)
- (the caller is asked to compute this because the macro expands POOL more than
- once, and for efficiency it's best for the caller to assign POOL_ADDR(P) to a
- variable and pass the latter to the macro; because Py_ADDRESS_IN_RANGE is
- called on every alloc/realloc/free, micro-efficiency is important here).
- Tricky: Let B be the arena base address associated with the pool, B =
- arenas[(POOL)->arenaindex].address. Then P belongs to the arena if and only if
- B <= P < B + ARENA_SIZE
- Subtracting B throughout, this is true iff
- 0 <= P-B < ARENA_SIZE
- By using unsigned arithmetic, the "0 <=" half of the test can be skipped.
- Obscure: A PyMem "free memory" function can call the pymalloc free or realloc
- before the first arena has been allocated. `arenas` is still NULL in that
- case. We're relying on that maxarenas is also 0 in that case, so that
- (POOL)->arenaindex < maxarenas must be false, saving us from trying to index
- into a NULL arenas.
- Details: given P and POOL, the arena_object corresponding to P is AO =
- arenas[(POOL)->arenaindex]. Suppose obmalloc controls P. Then (barring wild
- stores, etc), POOL is the correct address of P's pool, AO.address is the
- correct base address of the pool's arena, and P must be within ARENA_SIZE of
- AO.address. In addition, AO.address is not 0 (no arena can start at address 0
- (NULL)). Therefore Py_ADDRESS_IN_RANGE correctly reports that obmalloc
- controls P.
- Now suppose obmalloc does not control P (e.g., P was obtained via a direct
- call to the system malloc() or realloc()). (POOL)->arenaindex may be anything
- in this case -- it may even be uninitialized trash. If the trash arenaindex
- is >= maxarenas, the macro correctly concludes at once that obmalloc doesn't
- control P.
- Else arenaindex is < maxarena, and AO is read up. If AO corresponds to an
- allocated arena, obmalloc controls all the memory in slice AO.address :
- AO.address+ARENA_SIZE. By case assumption, P is not controlled by obmalloc,
- so P doesn't lie in that slice, so the macro correctly reports that P is not
- controlled by obmalloc.
- Finally, if P is not controlled by obmalloc and AO corresponds to an unused
- arena_object (one not currently associated with an allocated arena),
- AO.address is 0, and the second test in the macro reduces to:
- P < ARENA_SIZE
- If P >= ARENA_SIZE (extremely likely), the macro again correctly concludes
- that P is not controlled by obmalloc. However, if P < ARENA_SIZE, this part
- of the test still passes, and the third clause (AO.address != 0) is necessary
- to get the correct result: AO.address is 0 in this case, so the macro
- correctly reports that P is not controlled by obmalloc (despite that P lies in
- slice AO.address : AO.address + ARENA_SIZE).
- Note: The third (AO.address != 0) clause was added in Python 2.5. Before
- 2.5, arenas were never free()'ed, and an arenaindex < maxarena always
- corresponded to a currently-allocated arena, so the "P is not controlled by
- obmalloc, AO corresponds to an unused arena_object, and P < ARENA_SIZE" case
- was impossible.
- Note that the logic is excruciating, and reading up possibly uninitialized
- memory when P is not controlled by obmalloc (to get at (POOL)->arenaindex)
- creates problems for some memory debuggers. The overwhelming advantage is
- that this test determines whether an arbitrary address is controlled by
- obmalloc in a small constant time, independent of the number of arenas
- obmalloc controls. Since this test is needed at every entry point, it's
- extremely desirable that it be this fast.
- */
- #define Py_ADDRESS_IN_RANGE(P, POOL) \
- ((POOL)->arenaindex < maxarenas && \
- (uptr)(P) - arenas[(POOL)->arenaindex].address < (uptr)ARENA_SIZE && \
- arenas[(POOL)->arenaindex].address != 0)
- /* This is only useful when running memory debuggers such as
- * Purify or Valgrind. Uncomment to use.
- *
- #define Py_USING_MEMORY_DEBUGGER
- */
- #ifdef Py_USING_MEMORY_DEBUGGER
- /* Py_ADDRESS_IN_RANGE may access uninitialized memory by design
- * This leads to thousands of spurious warnings when using
- * Purify or Valgrind. By making a function, we can easily
- * suppress the uninitialized memory reads in this one function.
- * So we won't ignore real errors elsewhere.
- *
- * Disable the macro and use a function.
- */
- #undef Py_ADDRESS_IN_RANGE
- #if defined(__GNUC__) && ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 1) || \
- (__GNUC__ >= 4))
- #define Py_NO_INLINE __attribute__((__noinline__))
- #else
- #define Py_NO_INLINE
- #endif
- /* Don't make static, to try to ensure this isn't inlined. */
- int Py_ADDRESS_IN_RANGE(void *P, poolp pool) Py_NO_INLINE;
- #undef Py_NO_INLINE
- #endif
- /*==========================================================================*/
- /* malloc. Note that nbytes==0 tries to return a non-NULL pointer, distinct
- * from all other currently live pointers. This may not be possible.
- */
- /*
- * The basic blocks are ordered by decreasing execution frequency,
- * which minimizes the number of jumps in the most common cases,
- * improves branching prediction and instruction scheduling (small
- * block allocations typically result in a couple of instructions).
- * Unless the optimizer reorders everything, being too smart...
- */
- #undef PyObject_Malloc
- void *
- PyObject_Malloc(size_t nbytes)
- {
- block *bp;
- poolp pool;
- poolp next;
- uint size;
- /*
- * Limit ourselves to PY_SSIZE_T_MAX bytes to prevent security holes.
- * Most python internals blindly use a signed Py_ssize_t to track
- * things without checking for overflows or negatives.
- * As size_t is unsigned, checking for nbytes < 0 is not required.
- */
- if (nbytes > PY_SSIZE_T_MAX)
- return NULL;
- /*
- * This implicitly redirects malloc(0).
- */
- if ((nbytes - 1) < SMALL_REQUEST_THRESHOLD) {
- LOCK();
- /*
- * Most frequent paths first
- */
- size = (uint)(nbytes - 1) >> ALIGNMENT_SHIFT;
- pool = usedpools[size + size];
- if (pool != pool->nextpool) {
- /*
- * There is a used pool for this size class.
- * Pick up the head block of its free list.
- */
- ++pool->ref.count;
- bp = pool->freeblock;
- assert(bp != NULL);
- if ((pool->freeblock = *(block **)bp) != NULL) {
- UNLOCK();
- return (void *)bp;
- }
- /*
- * Reached the end of the free list, try to extend it.
- */
- if (pool->nextoffset <= pool->maxnextoffset) {
- /* There is room for another block. */
- pool->freeblock = (block*)pool +
- pool->nextoffset;
- pool->nextoffset += INDEX2SIZE(size);
- *(block **)(pool->freeblock) = NULL;
- UNLOCK();
- return (void *)bp;
- }
- /* Pool is full, unlink from used pools. */
- next = pool->nextpool;
- pool = pool->prevpool;
- next->prevpool = pool;
- pool->nextpool = next;
- UNLOCK();
- return (void *)bp;
- }
- /* There isn't a pool of the right size class immediately
- * available: use a free pool.
- */
- if (usable_arenas == NULL) {
- /* No arena has a free pool: allocate a new arena. */
- #ifdef WITH_MEMORY_LIMITS
- if (narenas_currently_allocated >= MAX_ARENAS) {
- UNLOCK();
- goto redirect;
- }
- #endif
- usable_arenas = new_arena();
- if (usable_arenas == NULL) {
- UNLOCK();
- goto redirect;
- }
- usable_arenas->nextarena =
- usable_arenas->prevarena = NULL;
- }
- assert(usable_arenas->address != 0);
- /* Try to get a cached free pool. */
- pool = usable_arenas->freepools;
- if (pool != NULL) {
- /* Unlink from cached pools. */
- usable_arenas->freepools = pool->nextpool;
- /* This arena already had the smallest nfreepools
- * value, so decreasing nfreepools doesn't change
- * that, and we don't need to rearrange the
- * usable_arenas list. However, if the arena has
- * become wholly allocated, we need to remove its
- * arena_object from usable_arenas.
- */
- --usable_arenas->nfreepools;
- if (usable_arenas->nfreepools == 0) {
- /* Wholly allocated: remove. */
- assert(usable_arenas->freepools == NULL);
- assert(usable_arenas->nextarena == NULL ||
- usable_arenas->nextarena->prevarena ==
- usable_arenas);
- usable_arenas = usable_arenas->nextarena;
- if (usable_arenas != NULL) {
- usable_arenas->prevarena = NULL;
- assert(usable_arenas->address != 0);
- }
- }
- else {
- /* nfreepools > 0: it must be that freepools
- * isn't NULL, or that we haven't yet carved
- * off all the arena's pools for the first
- * time.
- */
- assert(usable_arenas->freepools != NULL ||
- usable_arenas->pool_address <=
- (block*)usable_arenas->address +
- ARENA_SIZE - POOL_SIZE);
- }
- init_pool:
- /* Frontlink to used pools. */
- next = usedpools[size + size]; /* == prev */
- pool->nextpool = next;
- pool->prevpool = next;
- next->nextpool = pool;
- next->prevpool = pool;
- pool->ref.count = 1;
- if (pool->szidx == size) {
- /* Luckily, this pool last contained blocks
- * of the same size class, so its header
- * and free list are already initialized.
- */
- bp = pool->freeblock;
- pool->freeblock = *(block **)bp;
- UNLOCK();
- return (void *)bp;
- }
- /*
- * Initialize the pool header, set up the free list to
- * contain just the second block, and return the first
- * block.
- */
- pool->szidx = size;
- size = INDEX2SIZE(size);
- bp = (block *)pool + POOL_OVERHEAD;
- pool->nextoffset = POOL_OVERHEAD + (size << 1);
- pool->maxnextoffset = POOL_SIZE - size;
- pool->freeblock = bp + size;
- *(block **)(pool->freeblock) = NULL;
- UNLOCK();
- return (void *)bp;
- }
- /* Carve off a new pool. */
- assert(usable_arenas->nfreepools > 0);
- assert(usable_arenas->freepools == NULL);
- pool = (poolp)usable_arenas->pool_address;
- assert((block*)pool <= (block*)usable_arenas->address +
- ARENA_SIZE - POOL_SIZE);
- pool->arenaindex = usable_arenas - arenas;
- assert(&arenas[pool->arenaindex] == usable_arenas);
- pool->szidx = DUMMY_SIZE_IDX;
- usable_arenas->pool_address += POOL_SIZE;
- --usable_arenas->nfreepools;
- if (usable_arenas->nfreepools == 0) {
- assert(usable_arenas->nextarena == NULL ||
- usable_arenas->nextarena->prevarena ==
- usable_arenas);
- /* Unlink the arena: it is completely allocated. */
- usable_arenas = usable_arenas->nextarena;
- if (usable_arenas != NULL) {
- usable_arenas->prevarena = NULL;
- assert(usable_arenas->address != 0);
- }
- }
- goto init_pool;
- }
- /* The small block allocator ends here. */
- redirect:
- /* Redirect the original request to the underlying (libc) allocator.
- * We jump here on bigger requests, on error in the code above (as a
- * last chance to serve the request) or when the max memory limit
- * has been reached.
- */
- if (nbytes == 0)
- nbytes = 1;
- return (void *)malloc(nbytes);
- }
- /* free */
- #undef PyObject_Free
- void
- PyObject_Free(void *p)
- {
- poolp pool;
- block *lastfree;
- poolp next, prev;
- uint size;
- if (p == NULL) /* free(NULL) has no effect */
- return;
- pool = POOL_ADDR(p);
- if (Py_ADDRESS_IN_RANGE(p, pool)) {
- /* We allocated this address. */
- LOCK();
- /* Link p to the start of the pool's freeblock list. Since
- * the pool had at least the p block outstanding, the pool
- * wasn't empty (so it's already in a usedpools[] list, or
- * was full and is in no list -- it's not in the freeblocks
- * list in any case).
- */
- assert(pool->ref.count > 0); /* else it was empty */
- *(block **)p = lastfree = pool->freeblock;
- pool->freeblock = (block *)p;
- if (lastfree) {
- struct arena_object* ao;
- uint nf; /* ao->nfreepools */
- /* freeblock wasn't NULL, so the pool wasn't full,
- * and the pool is in a usedpools[] list.
- */
- if (--pool->ref.count != 0) {
- /* pool isn't empty: leave it in usedpools */
- UNLOCK();
- return;
- }
- /* Pool is now empty: unlink from usedpools, and
- * link to the front of freepools. This ensures that
- * previously freed pools will be allocated later
- * (being not referenced, they are perhaps paged out).
- */
- next = pool->nextpool;
- prev = pool->prevpool;
- next->prevpool = prev;
- prev->nextpool = next;
- /* Link the pool to freepools. This is a singly-linked
- * list, and pool->prevpool isn't used there.
- */
- ao = &arenas[pool->arenaindex];
- pool->nextpool = ao->freepools;
- ao->freepools = pool;
- nf = ++ao->nfreepools;
- /* All the rest is arena management. We just freed
- * a pool, and there are 4 cases for arena mgmt:
- * 1. If all the pools are free, return the arena to
- * the system free().
- * 2. If this is the only free pool in the arena,
- * add the arena back to the `usable_arenas` list.
- * 3. If the "next" arena has a smaller count of free
- * pools, we have to "slide this arena right" to
- * restore that usable_arenas is sorted in order of
- * nfreepools.
- * 4. Else there's nothing more to do.
- */
- if (nf == ao->ntotalpools) {
- /* Case 1. First unlink ao from usable_arenas.
- */
- assert(ao->prevarena == NULL ||
- ao->prevarena->address != 0);
- assert(ao ->nextarena == NULL ||
- ao->nextarena->address != 0);
- /* Fix the pointer in the prevarena, or the
- * usable_arenas pointer.
- */
- if (ao->prevarena == NULL) {
- usable_arenas = ao->nextarena;
- assert(usable_arenas == NULL ||
- usable_arenas->address != 0);
- }
- else {
- assert(ao->prevarena->nextarena == ao);
- ao->prevarena->nextarena =
- ao->nextarena;
- }
- /* Fix the pointer in the nextarena. */
- if (ao->nextarena != NULL) {
- assert(ao->nextarena->prevarena == ao);
- ao->nextarena->prevarena =
- ao->prevarena;
- }
- /* Record that this arena_object slot is
- * available to be reused.
- */
- ao->nextarena = unused_arena_objects;
- unused_arena_objects = ao;
- /* Free the entire arena. */
- free((void *)ao->address);
- ao->address = 0; /* mark unassociated */
- --narenas_currently_allocated;
- UNLOCK();
- return;
- }
- if (nf == 1) {
- /* Case 2. Put ao at the head of
- * usable_arenas. Note that because
- * ao->nfreepools was 0 before, ao isn't
- * currently on the usable_arenas list.
- */
- ao->nextarena = usable_arenas;
- ao->prevarena = NULL;
- if (usable_arenas)
- usable_arenas->prevarena = ao;
- usable_arenas = ao;
- assert(usable_arenas->address != 0);
- UNLOCK();
- return;
- }
- /* If this arena is now out of order, we need to keep
- * the list sorted. The list is kept sorted so that
- * the "most full" arenas are used first, which allows
- * the nearly empty arenas to be completely freed. In
- * a few un-scientific tests, it seems like this
- * approach allowed a lot more memory to be freed.
- */
- if (ao->nextarena == NULL ||
- nf <= ao->nextarena->nfreepools) {
- /* Case 4. Nothing to do. */
- UNLOCK();
- return;
- }
- /* Case 3: We have to move the arena towards the end
- * of the list, because it has more free pools than
- * the arena to its right.
- * First unlink ao from usable_arenas.
- */
- if (ao->prevarena != NULL) {
- /* ao isn't at the head of the list */
- assert(ao->prevarena->nextarena == ao);
- ao->prevarena->nextarena = ao->nextarena;
- }
- else {
- /* ao is at the head of the list */
- assert(usable_arenas == ao);
- usable_arenas = ao->nextarena;
- }
- ao->nextarena->prevarena = ao->prevarena;
- /* Locate the new insertion point by iterating over
- * the list, using our nextarena pointer.
- */
- while (ao->nextarena != NULL &&
- nf > ao->nextarena->nfreepools) {
- ao->prevarena = ao->nextarena;
- ao->nextarena = ao->nextarena->nextarena;
- }
- /* Insert ao at this point. */
- assert(ao->nextarena == NULL ||
- ao->prevarena == ao->nextarena->prevarena);
- assert(ao->prevarena->nextarena == ao->nextarena);
- ao->prevarena->nextarena = ao;
- if (ao->nextarena != NULL)
- ao->nextarena->prevarena = ao;
- /* Verify that the swaps worked. */
- assert(ao->nextarena == NULL ||
- nf <= ao->nextarena->nfreepools);
- assert(ao->prevarena == NULL ||
- nf > ao->prevarena->nfreepools);
- assert(ao->nextarena == NULL ||
- ao->nextarena->prevarena == ao);
- assert((usable_arenas == ao &&
- ao->prevarena == NULL) ||
- ao->prevarena->nextarena == ao);
- UNLOCK();
- return;
- }
- /* Pool was full, so doesn't currently live in any list:
- * link it to the front of the appropriate usedpools[] list.
- * This mimics LRU pool usage for new allocations and
- * targets optimal filling when several pools contain
- * blocks of the same size class.
- */
- --pool->ref.count;
- assert(pool->ref.count > 0); /* else the pool is empty */
- size = pool->szidx;
- next = usedpools[size + size];
- prev = next->prevpool;
- /* insert pool before next: prev <-> pool <-> next */
- pool->nextpool = next;
- pool->prevpool = prev;
- next->prevpool = pool;
- prev->nextpool = pool;
- UNLOCK();
- return;
- }
- /* We didn't allocate this address. */
- free(p);
- }
- /* realloc. If p is NULL, this acts like malloc(nbytes). Else if nbytes==0,
- * then as the Python docs promise, we do not treat this like free(p), and
- * return a non-NULL result.
- */
- #undef PyObject_Realloc
- void *
- PyObject_Realloc(void *p, size_t nbytes)
- {
- void *bp;
- poolp pool;
- size_t size;
- if (p == NULL)
- return PyObject_Malloc(nbytes);
- /*
- * Limit ourselves to PY_SSIZE_T_MAX bytes to prevent security holes.
- * Most python internals blindly use a signed Py_ssize_t to track
- * things without checking for overflows or negatives.
- * As size_t is unsigned, checking for nbytes < 0 is not required.
- */
- if (nbytes > PY_SSIZE_T_MAX)
- return NULL;
- pool = POOL_ADDR(p);
- if (Py_ADDRESS_IN_RANGE(p, pool)) {
- /* We're in charge of this block */
- size = INDEX2SIZE(pool->szidx);
- if (nbytes <= size) {
- /* The block is staying the same or shrinking. If
- * it's shrinking, there's a tradeoff: it costs
- * cycles to copy the block to a smaller size class,
- * but it wastes memory not to copy it. The
- * compromise here is to copy on shrink only if at
- * least 25% of size can be shaved off.
- */
- if (4 * nbytes > 3 * size) {
- /* It's the same,
- * or shrinking and new/old > 3/4.
- */
- return p;
- }
- size = nbytes;
- }
- bp = PyObject_Malloc(nbytes);
- if (bp != NULL) {
- memcpy(bp, p, size);
- PyObject_Free(p);
- }
- return bp;
- }
- /* We're not managing this block. If nbytes <=
- * SMALL_REQUEST_THRESHOLD, it's tempting to try to take over this
- * block. However, if we do, we need to copy the valid data from
- * the C-managed block to one of our blocks, and there's no portable
- * way to know how much of the memory space starting at p is valid.
- * As bug 1185883 pointed out the hard way, it's possible that the
- * C-managed block is "at the end" of allocated VM space, so that
- * a memory fault can occur if we try to copy nbytes bytes starting
- * at p. Instead we punt: let C continue to manage this block.
- */
- if (nbytes)
- return realloc(p, nbytes);
- /* C doesn't define the result of realloc(p, 0) (it may or may not
- * return NULL then), but Python's docs promise that nbytes==0 never
- * returns NULL. We don't pass 0 to realloc(), to avoid that endcase
- * to begin with. Even then, we can't be sure that realloc() won't
- * return NULL.
- */
- bp = realloc(p, 1);
- return bp ? bp : p;
- }
- #else /* ! WITH_PYMALLOC */
- /*==========================================================================*/
- /* pymalloc not enabled: Redirect the entry points to malloc. These will
- * only be used by extensions that are compiled with pymalloc enabled. */
- void *
- PyObject_Malloc(size_t n)
- {
- return PyMem_MALLOC(n);
- }
- void *
- PyObject_Realloc(void *p, size_t n)
- {
- return PyMem_REALLOC(p, n);
- }
- void
- PyObject_Free(void *p)
- {
- PyMem_FREE(p);
- }
- #endif /* WITH_PYMALLOC */
- #ifdef PYMALLOC_DEBUG
- /*==========================================================================*/
- /* A x-platform debugging allocator. This doesn't manage memory directly,
- * it wraps a real allocator, adding extra debugging info to the memory blocks.
- */
- /* Special bytes broadcast into debug memory blocks at appropriate times.
- * Strings of these are unlikely to be valid addresses, floats, ints or
- * 7-bit ASCII.
- */
- #undef CLEANBYTE
- #undef DEADBYTE
- #undef FORBIDDENBYTE
- #define CLEANBYTE 0xCB /* clean (newly allocated) memory */
- #define DEADBYTE 0xDB /* dead (newly freed) memory */
- #define FORBIDDENBYTE 0xFB /* untouchable bytes at each end of a block */
- static size_t serialno = 0; /* incremented on each debug {m,re}alloc */
- /* serialno is always incremented via calling this routine. The point is
- * to supply a single place to set a breakpoint.
- */
- static void
- bumpserialno(void)
- {
- ++serialno;
- }
- #define SST SIZEOF_SIZE_T
- /* Read sizeof(size_t) bytes at p as a big-endian size_t. */
- static size_t
- read_size_t(const void *p)
- {
- const uchar *q = (const uchar *)p;
- size_t result = *q++;
- int i;
- for (i = SST; --i > 0; ++q)
- result = (result << 8) | *q;
- return result;
- }
- /* Write n as a big-endian size_t, MSB at address p, LSB at
- * p + sizeof(size_t) - 1.
- */
- static void
- write_size_t(void *p, size_t n)
- {
- uchar *q = (uchar *)p + SST - 1;
- int i;
- for (i = SST; --i >= 0; --q) {
- *q = (uchar)(n & 0xff);
- n >>= 8;
- }
- }
- #ifdef Py_DEBUG
- /* Is target in the list? The list is traversed via the nextpool pointers.
- * The list may be NULL-terminated, or circular. Return 1 if target is in
- * list, else 0.
- */
- static int
- pool_is_in_list(const poolp target, poolp list)
- {
- poolp origlist = list;
- assert(target != NULL);
- if (list == NULL)
- return 0;
- do {
- if (target == list)
- return 1;
- list = list->nextpool;
- } while (list != NULL && list != origlist);
- return 0;
- }
- #else
- #define pool_is_in_list(X, Y) 1
- #endif /* Py_DEBUG */
- /* Let S = sizeof(size_t). The debug malloc asks for 4*S extra bytes and
- fills them with useful stuff, here calling the underlying malloc's result p:
- p[0: S]
- Number of bytes originally asked for. This is a size_t, big-endian (easier
- to read in a memory dump).
- p[S: 2*S]
- Copies of FORBIDDENBYTE. Used to catch under- writes and reads.
- p[2*S: 2*S+n]
- The requested memory, filled with copies of CLEANBYTE.
- Used to catch reference to uninitialized memory.
- &p[2*S] is returned. Note that this is 8-byte aligned if pymalloc
- handled the request itself.
- p[2*S+n: 2*S+n+S]
- Copies of FORBIDDENBYTE. Used to catch over- writes and reads.
- p[2*S+n+S: 2*S+n+2*S]
- A serial number, incremented by 1 on each call to _PyObject_DebugMalloc
- and _PyObject_DebugRealloc.
- This is a big-endian size_t.
- If "bad memory" is detected later, the serial number gives an
- excellent way to set a breakpoint on the next run, to capture the
- instant at which this block was passed out.
- */
- void *
- _PyObject_DebugMalloc(size_t nbytes)
- {
- uchar *p; /* base address of malloc'ed block */
- uchar *tail; /* p + 2*SST + nbytes == pointer to tail pad bytes */
- size_t total; /* nbytes + 4*SST */
- bumpserialno();
- total = nbytes + 4*SST;
- if (total < nbytes)
- /* overflow: can't represent total as a size_t */
- return NULL;
- p = (uchar *)PyObject_Malloc(total);
- if (p == NULL)
- return NULL;
- write_size_t(p, nbytes);
- memset(p + SST, FORBIDDENBYTE, SST);
- if (nbytes > 0)
- memset(p + 2*SST, CLEANBYTE, nbytes);
- tail = p + 2*SST + nbytes;
- memset(tail, FORBIDDENBYTE, SST);
- write_size_t(tail + SST, serialno);
- return p + 2*SST;
- }
- /* The debug free first checks the 2*SST bytes on each end for sanity (in
- particular, that the FORBIDDENBYTEs are still intact).
- Then fills the original bytes with DEADBYTE.
- Then calls the underlying free.
- */
- void
- _PyObject_DebugFree(void *p)
- {
- uchar *q = (uchar *)p - 2*SST; /* address returned from malloc */
- size_t nbytes;
- if (p == NULL)
- return;
- _PyObject_DebugCheckAddress(p);
- nbytes = read_size_t(q);
- if (nbytes > 0)
- memset(q, DEADBYTE, nbytes);
- PyObject_Free(q);
- }
- void *
- _PyObject_DebugRealloc(void *p, size_t nbytes)
- {
- uchar *q = (uchar *)p;
- uchar *tail;
- size_t total; /* nbytes + 4*SST */
- size_t original_nbytes;
- int i;
- if (p == NULL)
- return _PyObject_DebugMalloc(nbytes);
- _PyObject_DebugCheckAddress(p);
- bumpserialno();
- original_nbytes = read_size_t(q - 2*SST);
- total = nbytes + 4*SST;
- if (total < nbytes)
- /* overflow: can't represent total as a size_t */
- return NULL;
- if (nbytes < original_nbytes) {
- /* shrinking: mark old extra memory dead */
- memset(q + nbytes, DEADBYTE, original_nbytes - nbytes);
- }
- /* Resize and add decorations. */
- q = (uchar *)PyObject_Realloc(q - 2*SST, total);
- if (q == NULL)
- return NULL;
- write_size_t(q, nbytes);
- for (i = 0; i < SST; ++i)
- assert(q[SST + i] == FORBIDDENBYTE);
- q += 2*SST;
- tail = q + nbytes;
- memset(tail, FORBIDDENBYTE, SST);
- write_size_t(tail + SST, serialno);
- if (nbytes > original_nbytes) {
- /* growing: mark new extra memory clean */
- memset(q + original_nbytes, CLEANBYTE,
- nbytes - original_nbytes);
- }
- return q;
- }
- /* Check the forbidden bytes on both ends of the memory allocated for p.
- * If anything is wrong, print info to stderr via _PyObject_DebugDumpAddress,
- * and call Py_FatalError to kill the program.
- */
- void
- _PyObject_DebugCheckAddress(const void *p)
- {
- const uchar *q = (const uchar *)p;
- char *msg;
- size_t nbytes;
- const uchar *tail;
- int i;
- if (p == NULL) {
- msg = "didn't expect a NULL pointer";
- goto error;
- }
- /* Check the stuff at the start of p first: if there's underwrite
- * corruption, the number-of-bytes field may be nuts, and checking
- * the tail could lead to a segfault then.
- */
- for (i = SST; i >= 1; --i) {
- if (*(q-i) != FORBIDDENBYTE) {
- msg = "bad leading pad byte";
- goto error;
- }
- }
- nbytes = read_size_t(q - 2*SST);
- tail = q + nbytes;
- for (i = 0; i < SST; ++i) {
- if (tail[i] != FORBIDDENBYTE) {
- msg = "bad trailing pad byte";
- goto error;
- }
- }
- return;
- error:
- _PyObject_DebugDumpAddress(p);
- Py_FatalError(msg);
- }
- /* Display info to stderr about the memory block at p. */
- void
- _PyObject_DebugDumpAddress(const void *p)
- {
- const uchar *q = (const uchar *)p;
- const uchar *tail;
- size_t nbytes, serial;
- int i;
- int ok;
- fprintf(stderr, "Debug memory block at address p=%p:\n", p);
- if (p == NULL)
- return;
- nbytes = read_size_t(q - 2*SST);
- fprintf(stderr, " %" PY_FORMAT_SIZE_T "u bytes originally "
- "requested\n", nbytes);
- /* In case this is nuts, check the leading pad bytes first. */
- fprintf(stderr, " The %d pad bytes at p-%d are ", SST, SST);
- ok = 1;
- for (i = 1; i <= SST; ++i) {
- if (*(q-i) != FORBIDDENBYTE) {
- ok = 0;
- break;
- }
- }
- if (ok)
- fputs("FORBIDDENBYTE, as expected.\n", stderr);
- else {
- fprintf(stderr, "not all FORBIDDENBYTE (0x%02x):\n",
- FORBIDDENBYTE);
- for (i = SST; i >= 1; --i) {
- const uchar byte = *(q-i);
- fprintf(stderr, " at p-%d: 0x%02x", i, byte);
- if (byte != FORBIDDENBYTE)
- fputs(" *** OUCH", stderr);
- fputc('\n', stderr);
- }
- fputs(" Because memory is corrupted at the start, the "
- "count of bytes requested\n"
- " may be bogus, and checking the trailing pad "
- "bytes may segfault.\n", stderr);
- }
- tail = q + nbytes;
- fprintf(stderr, " The %d pad bytes at tail=%p are ", SST, tail);
- ok = 1;
- for (i = 0; i < SST; ++i) {
- if (tail[i] != FORBIDDENBYTE) {
- ok = 0;
- break;
- }
- }
- if (ok)
- fputs("FORBIDDENBYTE, as expected.\n", stderr);
- else {
- fprintf(stderr, "not all FORBIDDENBYTE (0x%02x):\n",
- FORBIDDENBYTE);
- for (i = 0; i < SST; ++i) {
- const uchar byte = tail[i];
- fprintf(stderr, " at tail+%d: 0x%02x",
- i, byte);
- if (byte != FORBIDDENBYTE)
- fputs(" *** OUCH", stderr);
- fputc('\n', stderr);
- }
- }
- serial = read_size_t(tail + SST);
- fprintf(stderr, " The block was made by call #%" PY_FORMAT_SIZE_T
- "u to debug malloc/realloc.\n", serial);
- if (nbytes > 0) {
- i = 0;
- fputs(" Data at p:", stderr);
- /* print up to 8 bytes at the start */
- while (q < tail && i < 8) {
- fprintf(stderr, " %02x", *q);
- ++i;
- ++q;
- }
- /* and up to 8 at the end */
- if (q < tail) {
- if (tail - q > 8) {
- fputs(" ...", stderr);
- q = tail - 8;
- }
- while (q < tail) {
- fprintf(stderr, " %02x", *q);
- ++q;
- }
- }
- fputc('\n', stderr);
- }
- }
- static size_t
- printone(const char* msg, size_t value)
- {
- int i, k;
- char buf[100];
- size_t origvalue = value;
- fputs(msg, stderr);
- for (i = (int)strlen(msg); i < 35; ++i)
- fputc(' ', stderr);
- fputc('=', stderr);
- /* Write the value with commas. */
- i = 22;
- buf[i--] = '\0';
- buf[i--] = '\n';
- k = 3;
- do {
- size_t nextvalue = value / 10;
- uint digit = (uint)(value - nextvalue * 10);
- value = nextvalue;
- buf[i--] = (char)(digit + '0');
- --k;
- if (k == 0 && value && i >= 0) {
- k = 3;
- buf[i--] = ',';
- }
- } while (value && i >= 0);
- while (i >= 0)
- buf[i--] = ' ';
- fputs(buf, stderr);
- return origvalue;
- }
- /* Print summary info to stderr about the state of pymalloc's structures.
- * In Py_DEBUG mode, also perform some expensive internal consistency
- * checks.
- */
- void
- _PyObject_DebugMallocStats(void)
- {
- uint i;
- const uint numclasses = SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT;
- /* # of pools, allocated blocks, and free blocks per class index */
- size_t numpools[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
- size_t numblocks[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
- size_t numfreeblocks[SMALL_REQUEST_THRESHOLD >> ALIGNMENT_SHIFT];
- /* total # of allocated bytes in used and full pools */
- size_t allocated_bytes = 0;
- /* total # of available bytes in used pools */
- size_t available_bytes = 0;
- /* # of free pools + pools not yet carved out of current arena */
- uint numfreepools = 0;
- /* # of bytes for arena alignment padding */
- size_t arena_alignment = 0;
- /* # of bytes in used and full pools used for pool_headers */
- size_t pool_header_bytes = 0;
- /* # of bytes in used and full pools wasted due to quantization,
- * i.e. the necessarily leftover space at the ends of used and
- * full pools.
- */
- size_t quantization = 0;
- /* # of arenas actually allocated. */
- size_t narenas = 0;
- /* running total -- should equal narenas * ARENA_SIZE */
- size_t total;
- char buf[128];
- fprintf(stderr, "Small block threshold = %d, in %u size classes.\n",
- SMALL_REQUEST_THRESHOLD, numclasses);
- for (i = 0; i < numclasses; ++i)
- numpools[i] = numblocks[i] = numfreeblocks[i] = 0;
- /* Because full pools aren't linked to from anything, it's easiest
- * to march over all the arenas. If we're lucky, most of the memory
- * will be living in full pools -- would be a shame to miss them.
- */
- for (i = 0; i < maxarenas; ++i) {
- uint poolsinarena;
- uint j;
- uptr base = arenas[i].address;
- /* Skip arenas which are not allocated. */
- if (arenas[i].address == (uptr)NULL)
- continue;
- narenas += 1;
- poolsinarena = arenas[i].ntotalpools;
- numfreepools += arenas[i].nfreepools;
- /* round up to pool alignment */
- if (base & (uptr)POOL_SIZE_MASK) {
- arena_alignment += POOL_SIZE;
- base &= ~(uptr)POOL_SIZE_MASK;
- base += POOL_SIZE;
- }
- /* visit every pool in the arena */
- assert(base <= (uptr) arenas[i].pool_address);
- for (j = 0;
- base < (uptr) arenas[i].pool_address;
- ++j, base += POOL_SIZE) {
- poolp p = (poolp)base;
- const uint sz = p->szidx;
- uint freeblocks;
- if (p->ref.count == 0) {
- /* currently unused */
- assert(pool_is_in_list(p, arenas[i].freepools));
- continue;
- }
- ++numpools[sz];
- numblocks[sz] += p->ref.count;
- freeblocks = NUMBLOCKS(sz) - p->ref.count;
- numfreeblocks[sz] += freeblocks;
- #ifdef Py_DEBUG
- if (freeblocks > 0)
- assert(pool_is_in_list(p, usedpools[sz + sz]));
- #endif
- }
- }
- assert(narenas == narenas_currently_allocated);
- fputc('\n', stderr);
- fputs("class size num pools blocks in use avail blocks\n"
- "----- ---- --------- ------------- ------------\n",
- stderr);
- for (i = 0; i < numclasses; ++i) {
- size_t p = numpools[i];
- size_t b = numblocks[i];
- size_t f = numfreeblocks[i];
- uint size = INDEX2SIZE(i);
- if (p == 0) {
- assert(b == 0 && f == 0);
- continue;
- }
- fprintf(stderr, "%5u %6u "
- "%11" PY_FORMAT_SIZE_T "u "
- "%15" PY_FORMAT_SIZE_T "u "
- "%13" PY_FORMAT_SIZE_T "u\n",
- i, size, p, b, f);
- allocated_bytes += b * size;
- available_bytes += f * size;
- pool_header_bytes += p * POOL_OVERHEAD;
- quantization += p * ((POOL_SIZE - POOL_OVERHEAD) % size);
- }
- fputc('\n', stderr);
- (void)printone("# times object malloc called", serialno);
- (void)printone("# arenas allocated total", ntimes_arena_allocated);
- (void)printone("# arenas reclaimed", ntimes_arena_allocated - narenas);
- (void)printone("# arenas highwater mark", narenas_highwater);
- (void)printone("# arenas allocated current", narenas);
- PyOS_snprintf(buf, sizeof(buf),
- "%" PY_FORMAT_SIZE_T "u arenas * %d bytes/arena",
- narenas, ARENA_SIZE);
- (void)printone(buf, narenas * ARENA_SIZE);
- fputc('\n', stderr);
- total = printone("# bytes in allocated blocks", allocated_bytes);
- total += printone("# bytes in available blocks", available_bytes);
- PyOS_snprintf(buf, sizeof(buf),
- "%u unused pools * %d bytes", numfreepools, POOL_SIZE);
- total += printone(buf, (size_t)numfreepools * POOL_SIZE);
- total += printone("# bytes lost to pool headers", pool_header_bytes);
- total += printone("# bytes lost to quantization", quantization);
- total += printone("# bytes lost to arena alignment", arena_alignment);
- (void)printone("Total", total);
- }
- #endif /* PYMALLOC_DEBUG */
- #ifdef Py_USING_MEMORY_DEBUGGER
- /* Make this function last so gcc won't inline it since the definition is
- * after the reference.
- */
- int
- Py_ADDRESS_IN_RANGE(void *P, poolp pool)
- {
- return pool->arenaindex < maxarenas &&
- (uptr)P - arenas[pool->arenaindex].address < (uptr)ARENA_SIZE &&
- arenas[pool->arenaindex].address != 0;
- }
- #endif