Tuning options that are also dynamically changeable via mallopt:
- DEFAULT_MXFAST 64 (for 32bit), 128 (for 64bit)
DEFAULT_TRIM_THRESHOLD 128 * 1024
DEFAULT_TOP_PAD 0
DEFAULT_MMAP_THRESHOLD 128 * 1024
corresponding parameter to the argument value if it can (i.e., so
long as the value is meaningful), and returns 1 if successful else
0. SVID/XPG/ANSI defines four standard param numbers for mallopt,
- normally defined in malloc.h. Only one of these (M_MXFAST) is used
- in this malloc. The others (M_NLBLKS, M_GRAIN, M_KEEP) don't apply,
- so setting them has no effect. But this malloc also supports four
- other options in mallopt. See below for details. Briefly, supported
- parameters are as follows (listed defaults are for "typical"
- configurations).
+ normally defined in malloc.h. These params (M_MXFAST, M_NLBLKS, M_GRAIN,
+ M_KEEP) don't apply to our malloc, so setting them has no effect. But this
+ malloc also supports four other options in mallopt. See below for details.
+ Briefly, supported parameters are as follows (listed defaults are for
+ "typical" configurations).
Symbol param # default allowed param values
- M_MXFAST 1 64 0-80 (0 disables fastbins)
+ M_MXFAST 1 64 0-80 (deprecated)
M_TRIM_THRESHOLD -1 128*1024 any (-1U disables trimming)
M_TOP_PAD -2 0 any
M_MMAP_THRESHOLD -3 128*1024 any (or 0 if no MMAP support)
/* mallopt tuning options */
-/*
- M_MXFAST is the maximum request size used for "fastbins", special bins
- that hold returned chunks without consolidating their spaces. This
- enables future requests for chunks of the same size to be handled
- very quickly, but can increase fragmentation, and thus increase the
- overall memory footprint of a program.
-
- This malloc manages fastbins very conservatively yet still
- efficiently, so fragmentation is rarely a problem for values less
- than or equal to the default. The maximum supported value of MXFAST
- is 80. You wouldn't want it any higher than this anyway. Fastbins
- are designed especially for use with many small structs, objects or
- strings -- the default handles structs/objects/arrays with sizes up
- to 8 4byte fields, or small strings representing words, tokens,
- etc. Using fastbins for larger objects normally worsens
- fragmentation without improving speed.
-
- M_MXFAST is set in REQUEST size units. It is internally used in
- chunksize units, which adds padding and alignment. You can reduce
- M_MXFAST to 0 to disable all use of fastbins. This causes the malloc
- algorithm to be a closer approximation of fifo-best-fit in all cases,
- not just for larger requests, but will generally cause it to be
- slower.
-*/
-
-
-/* M_MXFAST is a standard SVID/XPG tuning option, usually listed in malloc.h */
-#ifndef M_MXFAST
-#define M_MXFAST 1
-#endif
-
-#ifndef DEFAULT_MXFAST
-#define DEFAULT_MXFAST (64 * SIZE_SZ / 4)
-#endif
-
/*
M_TRIM_THRESHOLD is the maximum amount of unused top-most memory
#define unmark_bin(m, i) ((m)->binmap[idx2block (i)] &= ~(idx2bit (i)))
#define get_binmap(m, i) ((m)->binmap[idx2block (i)] & idx2bit (i))
-/*
- Fastbins
-
- An array of lists holding recently freed small chunks. Fastbins
- are not doubly linked. It is faster to single-link them, and
- since chunks are never removed from the middles of these lists,
- double linking is not necessary. Also, unlike regular bins, they
- are not even processed in FIFO order (they use faster LIFO) since
- ordering doesn't much matter in the transient contexts in which
- fastbins are normally used.
-
- Chunks in fastbins keep their inuse bit set, so they cannot
- be consolidated with other free chunks.
- */
-
-typedef struct malloc_chunk *mfastbinptr;
-#define fastbin(ar_ptr, idx) ((ar_ptr)->fastbinsY[idx])
-
-/* offset 2 to use otherwise unindexable first 2 bins */
-#define fastbin_index(sz) \
- ((((unsigned int) (sz)) >> (SIZE_SZ == 8 ? 4 : 3)) - 2)
-
-
-/* The maximum fastbin request size we support */
-#define MAX_FAST_SIZE (80 * SIZE_SZ / 4)
-
-#define NFASTBINS (fastbin_index (request2size (MAX_FAST_SIZE)) + 1)
/*
ATTEMPT_TRIMMING_THRESHOLD is the size of a chunk in free()
#define set_noncontiguous(M) ((M)->flags |= NONCONTIGUOUS_BIT)
#define set_contiguous(M) ((M)->flags &= ~NONCONTIGUOUS_BIT)
-/* Maximum size of memory handled in fastbins. */
-static uint8_t global_max_fast;
-
-/*
- Set value of max_fast.
- Use impossibly small value if 0.
- Precondition: there are no existing fastbin chunks in the main arena.
- Since do_check_malloc_state () checks this, we call malloc_consolidate ()
- before changing max_fast. Note other arenas will leak their fast bin
- entries if max_fast is reduced.
- */
-
-#define set_max_fast(s) \
- global_max_fast = (((size_t) (s) <= MALLOC_ALIGN_MASK - SIZE_SZ) \
- ? MIN_CHUNK_SIZE / 2 : ((s + SIZE_SZ) & ~MALLOC_ALIGN_MASK))
-
-static __always_inline INTERNAL_SIZE_T
-get_max_fast (void)
-{
- /* Tell the GCC optimizers that global_max_fast is never larger
- than MAX_FAST_SIZE. This avoids out-of-bounds array accesses in
- _int_malloc after constant propagation of the size parameter.
- (The code never executes because malloc preserves the
- global_max_fast invariant, but the optimizers may not recognize
- this.) */
- if (global_max_fast > MAX_FAST_SIZE)
- __builtin_unreachable ();
- return global_max_fast;
-}
/*
----------- Internal state representation and initialization -----------
/* Serialize access. */
__libc_lock_define (, mutex);
- /* Flags (formerly in max_fast). */
+ /* Flags */
int flags;
- /* Fastbins */
- mfastbinptr fastbinsY[NFASTBINS];
-
/* Base of the topmost chunk -- not otherwise kept in a bin */
mchunkptr top;
if (av != &main_arena)
#endif
set_noncontiguous (av);
- if (av == &main_arena)
- set_max_fast (DEFAULT_MXFAST);
av->top = initial_top (av);
}
static __always_inline int
do_set_mxfast (size_t value)
{
- if (value <= MAX_FAST_SIZE)
- {
- LIBC_PROBE (memory_mallopt_mxfast, 2, value, get_max_fast ());
- set_max_fast (value);
- return 1;
- }
- return 0;
+ return 1;
}
static __always_inline int
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