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Modify pages_map() to support mapping uncommitted virtual memory.

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If the OS overcommits:
- Commit all mappings in pages_map() regardless of whether the caller
  requested committed memory.
- Linux-specific: Specify MAP_NORESERVE to avoid
  unfortunate interactions with heuristic overcommit mode during
  fork(2).

This resolves #193.
This commit is contained in:
Jason Evans 2016-05-05 17:45:02 -07:00
parent dc391adc65
commit c2f970c32b
7 changed files with 117 additions and 27 deletions
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2
configure.ac
View File

@ -305,6 +305,7 @@ case "${host}" in
*-*-freebsd*)
CFLAGS="$CFLAGS"
abi="elf"
AC_DEFINE([JEMALLOC_SYSCTL_VM_OVERCOMMIT], [ ])
AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
force_lazy_lock="1"
;;
@ -329,6 +330,7 @@ case "${host}" in
CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
abi="elf"
AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED], [ ])
AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
AC_DEFINE([JEMALLOC_USE_CXX_THROW], [ ])

9
include/jemalloc/internal/jemalloc_internal_defs.h.in
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@ -214,6 +214,15 @@
#undef JEMALLOC_ZONE
#undef JEMALLOC_ZONE_VERSION
/*
* Methods for determining whether the OS overcommits.
* JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY: Linux's
* /proc/sys/vm.overcommit_memory file.
* JEMALLOC_SYSCTL_VM_OVERCOMMIT: FreeBSD's vm.overcommit sysctl.
*/
#undef JEMALLOC_SYSCTL_VM_OVERCOMMIT
#undef JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY
/*
* Methods for purging unused pages differ between operating systems.
*

5
include/jemalloc/internal/pages.h
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@ -9,13 +9,14 @@
/******************************************************************************/
#ifdef JEMALLOC_H_EXTERNS
void *pages_map(void *addr, size_t size);
void *pages_map(void *addr, size_t size, bool *commit);
void pages_unmap(void *addr, size_t size);
void *pages_trim(void *addr, size_t alloc_size, size_t leadsize,
size_t size);
size_t size, bool *commit);
bool pages_commit(void *addr, size_t size);
bool pages_decommit(void *addr, size_t size);
bool pages_purge(void *addr, size_t size);
void pages_boot(void);
#endif /* JEMALLOC_H_EXTERNS */
/******************************************************************************/

1
include/jemalloc/internal/private_symbols.txt
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@ -398,6 +398,7 @@ opt_utrace
opt_xmalloc
opt_zero
p2rz
pages_boot
pages_commit
pages_decommit
pages_map

10
src/chunk_mmap.c
View File

@ -16,18 +16,16 @@ chunk_alloc_mmap_slow(size_t size, size_t alignment, bool *zero, bool *commit)
do {
void *pages;
size_t leadsize;
pages = pages_map(NULL, alloc_size);
pages = pages_map(NULL, alloc_size, commit);
if (pages == NULL)
return (NULL);
leadsize = ALIGNMENT_CEILING((uintptr_t)pages, alignment) -
(uintptr_t)pages;
ret = pages_trim(pages, alloc_size, leadsize, size);
ret = pages_trim(pages, alloc_size, leadsize, size, commit);
} while (ret == NULL);
assert(ret != NULL);
*zero = true;
if (!*commit)
*commit = pages_decommit(ret, size);
return (ret);
}
@ -54,7 +52,7 @@ chunk_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
assert(alignment != 0);
assert((alignment & chunksize_mask) == 0);
ret = pages_map(new_addr, size);
ret = pages_map(new_addr, size, commit);
if (ret == NULL || ret == new_addr)
return (ret);
assert(new_addr == NULL);
@ -66,8 +64,6 @@ chunk_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
assert(ret != NULL);
*zero = true;
if (!*commit)
*commit = pages_decommit(ret, size);
return (ret);
}

1
src/jemalloc.c
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@ -1272,6 +1272,7 @@ malloc_init_hard_a0_locked(tsd_t *tsd)
abort();
}
}
pages_boot();
if (base_boot())
return (true);
if (chunk_boot())

116
src/pages.c
View File

@ -1,29 +1,49 @@
#define JEMALLOC_PAGES_C_
#include "jemalloc/internal/jemalloc_internal.h"
#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
#include <sys/sysctl.h>
#endif
/******************************************************************************/
/* Data. */
#ifndef _WIN32
# define PAGES_PROT_COMMIT (PROT_READ | PROT_WRITE)
# define PAGES_PROT_DECOMMIT (PROT_NONE)
static int mmap_flags;
#endif
static bool os_overcommits;
/******************************************************************************/
void *
pages_map(void *addr, size_t size)
pages_map(void *addr, size_t size, bool *commit)
{
void *ret;
assert(size != 0);
if (os_overcommits)
*commit = true;
#ifdef _WIN32
/*
* If VirtualAlloc can't allocate at the given address when one is
* given, it fails and returns NULL.
*/
ret = VirtualAlloc(addr, size, MEM_COMMIT | MEM_RESERVE,
ret = VirtualAlloc(addr, size, MEM_RESERVE | (*commit ? MEM_COMMIT : 0),
PAGE_READWRITE);
#else
/*
* We don't use MAP_FIXED here, because it can cause the *replacement*
* of existing mappings, and we only want to create new mappings.
*/
ret = mmap(addr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON,
-1, 0);
{
int prot = *commit ? PAGES_PROT_COMMIT : PAGES_PROT_DECOMMIT;
ret = mmap(addr, size, prot, mmap_flags, -1, 0);
}
assert(ret != NULL);
if (ret == MAP_FAILED)
@ -67,7 +87,8 @@ pages_unmap(void *addr, size_t size)
}
void *
pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size)
pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size,
bool *commit)
{
void *ret = (void *)((uintptr_t)addr + leadsize);
@ -77,7 +98,7 @@ pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size)
void *new_addr;
pages_unmap(addr, alloc_size);
new_addr = pages_map(ret, size);
new_addr = pages_map(ret, size, commit);
if (new_addr == ret)
return (ret);
if (new_addr)
@ -101,17 +122,17 @@ static bool
pages_commit_impl(void *addr, size_t size, bool commit)
{
#ifndef _WIN32
/*
* The following decommit/commit implementation is functional, but
* always disabled because it doesn't add value beyong improved
* debugging (at the cost of extra system calls) on systems that
* overcommit.
*/
if (false) {
int prot = commit ? (PROT_READ | PROT_WRITE) : PROT_NONE;
void *result = mmap(addr, size, prot, MAP_PRIVATE | MAP_ANON |
MAP_FIXED, -1, 0);
if (os_overcommits)
return (true);
#ifdef _WIN32
return (commit ? (addr != VirtualAlloc(addr, size, MEM_COMMIT,
PAGE_READWRITE)) : (!VirtualFree(addr, size, MEM_DECOMMIT)));
#else
{
int prot = commit ? PAGES_PROT_COMMIT : PAGES_PROT_DECOMMIT;
void *result = mmap(addr, size, prot, mmap_flags | MAP_FIXED,
-1, 0);
if (result == MAP_FAILED)
return (true);
if (result != addr) {
@ -125,7 +146,6 @@ pages_commit_impl(void *addr, size_t size, bool commit)
return (false);
}
#endif
return (true);
}
bool
@ -171,3 +191,63 @@ pages_purge(void *addr, size_t size)
return (unzeroed);
}
#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
static bool
os_overcommits_sysctl(void)
{
int vm_overcommit;
size_t sz;
sz = sizeof(vm_overcommit);
if (sysctlbyname("vm.overcommit", &vm_overcommit, &sz, NULL, 0) != 0)
return (false); /* Error. */
return ((vm_overcommit & 0x3) == 0);
}
#endif
#ifdef JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY
static bool
os_overcommits_proc(void)
{
int fd;
char buf[1];
ssize_t nread;
fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
if (fd == -1)
return (false); /* Error. */
nread = read(fd, &buf, sizeof(buf));
if (nread < 1)
return (false); /* Error. */
/*
* /proc/sys/vm/overcommit_memory meanings:
* 0: Heuristic overcommit.
* 1: Always overcommit.
* 2: Never overcommit.
*/
return (buf[0] == '0' || buf[0] == '1');
}
#endif
void
pages_boot(void)
{
#ifndef _WIN32
mmap_flags = MAP_PRIVATE | MAP_ANON;
#endif
#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
os_overcommits = os_overcommits_sysctl();
#elif defined(JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY)
os_overcommits = os_overcommits_proc();
# ifdef MAP_NORESERVE
if (os_overcommits)
mmap_flags |= MAP_NORESERVE;
# endif
#else
os_overcommits = false;
#endif
}