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malloc: Move mmap logic to its own function

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So it can be used with different pagesize and flags.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Adhemerval Zanella 2021-08-16 11:14:20 -03:00
parent 7478c9959a
commit 6cc3ccc67e
1 changed files with 88 additions and 76 deletions
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164
malloc/malloc.c
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@ -2412,6 +2412,85 @@ do_check_malloc_state (mstate av)
be extended or replaced.
*/
static void *
sysmalloc_mmap (INTERNAL_SIZE_T nb, size_t pagesize, int extra_flags, mstate av)
{
long int size;
/*
Round up size to nearest page. For mmapped chunks, the overhead is one
SIZE_SZ unit larger than for normal chunks, because there is no
following chunk whose prev_size field could be used.
See the front_misalign handling below, for glibc there is no need for
further alignments unless we have have high alignment.
*/
if (MALLOC_ALIGNMENT == CHUNK_HDR_SZ)
size = ALIGN_UP (nb + SIZE_SZ, pagesize);
else
size = ALIGN_UP (nb + SIZE_SZ + MALLOC_ALIGN_MASK, pagesize);
/* Don't try if size wraps around 0. */
if ((unsigned long) (size) <= (unsigned long) (nb))
return MAP_FAILED;
char *mm = (char *) MMAP (0, size,
mtag_mmap_flags | PROT_READ | PROT_WRITE,
extra_flags);
if (mm == MAP_FAILED)
return mm;
madvise_thp (mm, size);
/*
The offset to the start of the mmapped region is stored in the prev_size
field of the chunk. This allows us to adjust returned start address to
meet alignment requirements here and in memalign(), and still be able to
compute proper address argument for later munmap in free() and realloc().
*/
INTERNAL_SIZE_T front_misalign; /* unusable bytes at front of new space */
if (MALLOC_ALIGNMENT == CHUNK_HDR_SZ)
{
/* For glibc, chunk2mem increases the address by CHUNK_HDR_SZ and
MALLOC_ALIGN_MASK is CHUNK_HDR_SZ-1. Each mmap'ed area is page
aligned and therefore definitely MALLOC_ALIGN_MASK-aligned. */
assert (((INTERNAL_SIZE_T) chunk2mem (mm) & MALLOC_ALIGN_MASK) == 0);
front_misalign = 0;
}
else
front_misalign = (INTERNAL_SIZE_T) chunk2mem (mm) & MALLOC_ALIGN_MASK;
mchunkptr p; /* the allocated/returned chunk */
if (front_misalign > 0)
{
ptrdiff_t correction = MALLOC_ALIGNMENT - front_misalign;
p = (mchunkptr) (mm + correction);
set_prev_size (p, correction);
set_head (p, (size - correction) | IS_MMAPPED);
}
else
{
p = (mchunkptr) mm;
set_prev_size (p, 0);
set_head (p, size | IS_MMAPPED);
}
/* update statistics */
int new = atomic_exchange_and_add (&mp_.n_mmaps, 1) + 1;
atomic_max (&mp_.max_n_mmaps, new);
unsigned long sum;
sum = atomic_exchange_and_add (&mp_.mmapped_mem, size) + size;
atomic_max (&mp_.max_mmapped_mem, sum);
check_chunk (av, p);
return chunk2mem (p);
}
static void *
sysmalloc (INTERNAL_SIZE_T nb, mstate av)
{
@ -2449,81 +2528,10 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
|| ((unsigned long) (nb) >= (unsigned long) (mp_.mmap_threshold)
&& (mp_.n_mmaps < mp_.n_mmaps_max)))
{
char *mm; /* return value from mmap call*/
try_mmap:
/*
Round up size to nearest page. For mmapped chunks, the overhead
is one SIZE_SZ unit larger than for normal chunks, because there
is no following chunk whose prev_size field could be used.
See the front_misalign handling below, for glibc there is no
need for further alignments unless we have have high alignment.
*/
if (MALLOC_ALIGNMENT == CHUNK_HDR_SZ)
size = ALIGN_UP (nb + SIZE_SZ, pagesize);
else
size = ALIGN_UP (nb + SIZE_SZ + MALLOC_ALIGN_MASK, pagesize);
char *mm = sysmalloc_mmap (nb, pagesize, 0, av);
if (mm != MAP_FAILED)
return mm;
tried_mmap = true;
/* Don't try if size wraps around 0 */
if ((unsigned long) (size) > (unsigned long) (nb))
{
mm = (char *) (MMAP (0, size,
mtag_mmap_flags | PROT_READ | PROT_WRITE, 0));
if (mm != MAP_FAILED)
{
madvise_thp (mm, size);
/*
The offset to the start of the mmapped region is stored
in the prev_size field of the chunk. This allows us to adjust
returned start address to meet alignment requirements here
and in memalign(), and still be able to compute proper
address argument for later munmap in free() and realloc().
*/
if (MALLOC_ALIGNMENT == CHUNK_HDR_SZ)
{
/* For glibc, chunk2mem increases the address by
CHUNK_HDR_SZ and MALLOC_ALIGN_MASK is
CHUNK_HDR_SZ-1. Each mmap'ed area is page
aligned and therefore definitely
MALLOC_ALIGN_MASK-aligned. */
assert (((INTERNAL_SIZE_T) chunk2mem (mm) & MALLOC_ALIGN_MASK) == 0);
front_misalign = 0;
}
else
front_misalign = (INTERNAL_SIZE_T) chunk2mem (mm) & MALLOC_ALIGN_MASK;
if (front_misalign > 0)
{
correction = MALLOC_ALIGNMENT - front_misalign;
p = (mchunkptr) (mm + correction);
set_prev_size (p, correction);
set_head (p, (size - correction) | IS_MMAPPED);
}
else
{
p = (mchunkptr) mm;
set_prev_size (p, 0);
set_head (p, size | IS_MMAPPED);
}
/* update statistics */
int new = atomic_exchange_and_add (&mp_.n_mmaps, 1) + 1;
atomic_max (&mp_.max_n_mmaps, new);
unsigned long sum;
sum = atomic_exchange_and_add (&mp_.mmapped_mem, size) + size;
atomic_max (&mp_.max_mmapped_mem, sum);
check_chunk (av, p);
return chunk2mem (p);
}
}
}
/* There are no usable arenas and mmap also failed. */
@ -2600,8 +2608,12 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
}
}
else if (!tried_mmap)
/* We can at least try to use to mmap memory. */
goto try_mmap;
{
/* We can at least try to use to mmap memory. */
char *mm = sysmalloc_mmap (nb, pagesize, 0, av);
if (mm != MAP_FAILED)
return mm;
}
}
else /* av == main_arena */