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#define JEMALLOC_CHUNK_MMAP_C_
#include "jemalloc/internal/jemalloc_internal.h"
/******************************************************************************/
/* Data. */
/*
* Used by chunk_alloc_mmap() to decide whether to attempt the fast path and
* potentially avoid some system calls.
*/
#ifndef NO_TLS
static __thread bool mmap_unaligned_tls
JEMALLOC_ATTR(tls_model("initial-exec"));
#define MMAP_UNALIGNED_GET() mmap_unaligned_tls
#define MMAP_UNALIGNED_SET(v) do { \
mmap_unaligned_tls = (v); \
} while (0)
#else
static pthread_key_t mmap_unaligned_tsd;
#define MMAP_UNALIGNED_GET() ((bool)pthread_getspecific(mmap_unaligned_tsd))
#define MMAP_UNALIGNED_SET(v) do { \
pthread_setspecific(mmap_unaligned_tsd, (void *)(v)); \
} while (0)
#endif
/******************************************************************************/
/* Function prototypes for non-inline static functions. */
static void *pages_map(void *addr, size_t size, bool noreserve);
static void pages_unmap(void *addr, size_t size);
static void *chunk_alloc_mmap_slow(size_t size, bool unaligned,
bool noreserve);
static void *chunk_alloc_mmap_internal(size_t size, bool noreserve);
/******************************************************************************/
static void *
pages_map(void *addr, size_t size, bool noreserve)
{
void *ret;
/*
* We don't use MAP_FIXED here, because it can cause the *replacement*
* of existing mappings, and we only want to create new mappings.
*/
int flags = MAP_PRIVATE | MAP_ANON;
#ifdef MAP_NORESERVE
if (noreserve)
flags |= MAP_NORESERVE;
#endif
ret = mmap(addr, size, PROT_READ | PROT_WRITE, flags, -1, 0);
assert(ret != NULL);
if (ret == MAP_FAILED)
ret = NULL;
else if (addr != NULL && ret != addr) {
/*
* We succeeded in mapping memory, but not in the right place.
*/
if (munmap(ret, size) == -1) {
char buf[BUFERROR_BUF];
buferror(errno, buf, sizeof(buf));
malloc_write("<jemalloc>: Error in munmap(): ");
malloc_write(buf);
malloc_write("\n");
if (opt_abort)
abort();
}
ret = NULL;
}
assert(ret == NULL || (addr == NULL && ret != addr)
|| (addr != NULL && ret == addr));
return (ret);
}
static void
pages_unmap(void *addr, size_t size)
{
if (munmap(addr, size) == -1) {
char buf[BUFERROR_BUF];
buferror(errno, buf, sizeof(buf));
malloc_write("<jemalloc>: Error in munmap(): ");
malloc_write(buf);
malloc_write("\n");
if (opt_abort)
abort();
}
}
static void *
chunk_alloc_mmap_slow(size_t size, bool unaligned, bool noreserve)
{
void *ret;
size_t offset;
/* Beware size_t wrap-around. */
if (size + chunksize <= size)
return (NULL);
ret = pages_map(NULL, size + chunksize, noreserve);
if (ret == NULL)
return (NULL);
/* Clean up unneeded leading/trailing space. */
offset = CHUNK_ADDR2OFFSET(ret);
if (offset != 0) {
/* Note that mmap() returned an unaligned mapping. */
unaligned = true;
/* Leading space. */
pages_unmap(ret, chunksize - offset);
ret = (void *)((uintptr_t)ret +
(chunksize - offset));
/* Trailing space. */
pages_unmap((void *)((uintptr_t)ret + size),
offset);
} else {
/* Trailing space only. */
pages_unmap((void *)((uintptr_t)ret + size),
chunksize);
}
/*
* If mmap() returned an aligned mapping, reset mmap_unaligned so that
* the next chunk_alloc_mmap() execution tries the fast allocation
* method.
*/
if (unaligned == false)
MMAP_UNALIGNED_SET(false);
return (ret);
}
static void *
chunk_alloc_mmap_internal(size_t size, bool noreserve)
{
void *ret;
/*
* Ideally, there would be a way to specify alignment to mmap() (like
* NetBSD has), but in the absence of such a feature, we have to work
* hard to efficiently create aligned mappings. The reliable, but
* slow method is to create a mapping that is over-sized, then trim the
* excess. However, that always results in at least one call to
* pages_unmap().
*
* A more optimistic approach is to try mapping precisely the right
* amount, then try to append another mapping if alignment is off. In
* practice, this works out well as long as the application is not
* interleaving mappings via direct mmap() calls. If we do run into a
* situation where there is an interleaved mapping and we are unable to
* extend an unaligned mapping, our best option is to switch to the
* slow method until mmap() returns another aligned mapping. This will
* tend to leave a gap in the memory map that is too small to cause
* later problems for the optimistic method.
*
* Another possible confounding factor is address space layout
* randomization (ASLR), which causes mmap(2) to disregard the
* requested address. mmap_unaligned tracks whether the previous
* chunk_alloc_mmap() execution received any unaligned or relocated
* mappings, and if so, the current execution will immediately fall
* back to the slow method. However, we keep track of whether the fast
* method would have succeeded, and if so, we make a note to try the
* fast method next time.
*/
if (MMAP_UNALIGNED_GET() == false) {
size_t offset;
ret = pages_map(NULL, size, noreserve);
if (ret == NULL)
return (NULL);
offset = CHUNK_ADDR2OFFSET(ret);
if (offset != 0) {
MMAP_UNALIGNED_SET(true);
/* Try to extend chunk boundary. */
if (pages_map((void *)((uintptr_t)ret + size),
chunksize - offset, noreserve) == NULL) {
/*
* Extension failed. Clean up, then revert to
* the reliable-but-expensive method.
*/
pages_unmap(ret, size);
ret = chunk_alloc_mmap_slow(size, true,
noreserve);
} else {
/* Clean up unneeded leading space. */
pages_unmap(ret, chunksize - offset);
ret = (void *)((uintptr_t)ret + (chunksize -
offset));
}
}
} else
ret = chunk_alloc_mmap_slow(size, false, noreserve);
return (ret);
}
void *
chunk_alloc_mmap(size_t size)
{
return (chunk_alloc_mmap_internal(size, false));
}
void *
chunk_alloc_mmap_noreserve(size_t size)
{
return (chunk_alloc_mmap_internal(size, true));
}
void
chunk_dealloc_mmap(void *chunk, size_t size)
{
pages_unmap(chunk, size);
}
bool
chunk_mmap_boot(void)
{
#ifdef NO_TLS
if (pthread_key_create(&mmap_unaligned_tsd, NULL) != 0) {
malloc_write("<jemalloc>: Error in pthread_key_create()\n");
return (true);
}
#endif
return (false);
}
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