Modify pages_map() to support mapping uncommitted virtual memory.
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.
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@ -305,6 +305,7 @@ case "${host}" in
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*-*-freebsd*)
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CFLAGS="$CFLAGS"
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abi="elf"
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AC_DEFINE([JEMALLOC_SYSCTL_VM_OVERCOMMIT], [ ])
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AC_DEFINE([JEMALLOC_PURGE_MADVISE_FREE], [ ])
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force_lazy_lock="1"
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;;
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@ -329,6 +330,7 @@ case "${host}" in
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CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
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abi="elf"
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AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
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AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
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AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED], [ ])
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AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
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AC_DEFINE([JEMALLOC_USE_CXX_THROW], [ ])
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@ -214,6 +214,15 @@
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#undef JEMALLOC_ZONE
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#undef JEMALLOC_ZONE_VERSION
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/*
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* Methods for determining whether the OS overcommits.
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* JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY: Linux's
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* /proc/sys/vm.overcommit_memory file.
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* JEMALLOC_SYSCTL_VM_OVERCOMMIT: FreeBSD's vm.overcommit sysctl.
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*/
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#undef JEMALLOC_SYSCTL_VM_OVERCOMMIT
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#undef JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY
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/*
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* Methods for purging unused pages differ between operating systems.
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*
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@ -9,13 +9,14 @@
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/******************************************************************************/
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#ifdef JEMALLOC_H_EXTERNS
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void *pages_map(void *addr, size_t size);
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void *pages_map(void *addr, size_t size, bool *commit);
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void pages_unmap(void *addr, size_t size);
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void *pages_trim(void *addr, size_t alloc_size, size_t leadsize,
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size_t size);
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size_t size, bool *commit);
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bool pages_commit(void *addr, size_t size);
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bool pages_decommit(void *addr, size_t size);
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bool pages_purge(void *addr, size_t size);
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void pages_boot(void);
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#endif /* JEMALLOC_H_EXTERNS */
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/******************************************************************************/
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@ -398,6 +398,7 @@ opt_utrace
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opt_xmalloc
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opt_zero
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p2rz
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pages_boot
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pages_commit
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pages_decommit
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pages_map
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@ -16,18 +16,16 @@ chunk_alloc_mmap_slow(size_t size, size_t alignment, bool *zero, bool *commit)
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do {
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void *pages;
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size_t leadsize;
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pages = pages_map(NULL, alloc_size);
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pages = pages_map(NULL, alloc_size, commit);
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if (pages == NULL)
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return (NULL);
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leadsize = ALIGNMENT_CEILING((uintptr_t)pages, alignment) -
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(uintptr_t)pages;
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ret = pages_trim(pages, alloc_size, leadsize, size);
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ret = pages_trim(pages, alloc_size, leadsize, size, commit);
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} while (ret == NULL);
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assert(ret != NULL);
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*zero = true;
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if (!*commit)
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*commit = pages_decommit(ret, size);
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return (ret);
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}
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@ -54,7 +52,7 @@ chunk_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
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assert(alignment != 0);
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assert((alignment & chunksize_mask) == 0);
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ret = pages_map(new_addr, size);
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ret = pages_map(new_addr, size, commit);
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if (ret == NULL || ret == new_addr)
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return (ret);
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assert(new_addr == NULL);
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@ -66,8 +64,6 @@ chunk_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
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assert(ret != NULL);
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*zero = true;
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if (!*commit)
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*commit = pages_decommit(ret, size);
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return (ret);
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}
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@ -1272,6 +1272,7 @@ malloc_init_hard_a0_locked(tsd_t *tsd)
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abort();
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}
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}
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pages_boot();
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if (base_boot())
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return (true);
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if (chunk_boot())
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116
src/pages.c
116
src/pages.c
@ -1,29 +1,49 @@
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#define JEMALLOC_PAGES_C_
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#include "jemalloc/internal/jemalloc_internal.h"
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#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
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#include <sys/sysctl.h>
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#endif
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/******************************************************************************/
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/* Data. */
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#ifndef _WIN32
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# define PAGES_PROT_COMMIT (PROT_READ | PROT_WRITE)
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# define PAGES_PROT_DECOMMIT (PROT_NONE)
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static int mmap_flags;
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#endif
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static bool os_overcommits;
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/******************************************************************************/
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void *
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pages_map(void *addr, size_t size)
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pages_map(void *addr, size_t size, bool *commit)
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{
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void *ret;
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assert(size != 0);
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if (os_overcommits)
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*commit = true;
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#ifdef _WIN32
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/*
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* If VirtualAlloc can't allocate at the given address when one is
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* given, it fails and returns NULL.
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*/
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ret = VirtualAlloc(addr, size, MEM_COMMIT | MEM_RESERVE,
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ret = VirtualAlloc(addr, size, MEM_RESERVE | (*commit ? MEM_COMMIT : 0),
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PAGE_READWRITE);
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#else
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/*
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* We don't use MAP_FIXED here, because it can cause the *replacement*
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* of existing mappings, and we only want to create new mappings.
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*/
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ret = mmap(addr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON,
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-1, 0);
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{
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int prot = *commit ? PAGES_PROT_COMMIT : PAGES_PROT_DECOMMIT;
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ret = mmap(addr, size, prot, mmap_flags, -1, 0);
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}
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assert(ret != NULL);
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if (ret == MAP_FAILED)
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@ -67,7 +87,8 @@ pages_unmap(void *addr, size_t size)
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}
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void *
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pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size)
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pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size,
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bool *commit)
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{
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void *ret = (void *)((uintptr_t)addr + leadsize);
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@ -77,7 +98,7 @@ pages_trim(void *addr, size_t alloc_size, size_t leadsize, size_t size)
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void *new_addr;
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pages_unmap(addr, alloc_size);
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new_addr = pages_map(ret, size);
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new_addr = pages_map(ret, size, commit);
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if (new_addr == ret)
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return (ret);
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if (new_addr)
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@ -101,17 +122,17 @@ static bool
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pages_commit_impl(void *addr, size_t size, bool commit)
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{
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#ifndef _WIN32
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/*
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* The following decommit/commit implementation is functional, but
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* always disabled because it doesn't add value beyong improved
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* debugging (at the cost of extra system calls) on systems that
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* overcommit.
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*/
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if (false) {
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int prot = commit ? (PROT_READ | PROT_WRITE) : PROT_NONE;
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void *result = mmap(addr, size, prot, MAP_PRIVATE | MAP_ANON |
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MAP_FIXED, -1, 0);
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if (os_overcommits)
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return (true);
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#ifdef _WIN32
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return (commit ? (addr != VirtualAlloc(addr, size, MEM_COMMIT,
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PAGE_READWRITE)) : (!VirtualFree(addr, size, MEM_DECOMMIT)));
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#else
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{
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int prot = commit ? PAGES_PROT_COMMIT : PAGES_PROT_DECOMMIT;
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void *result = mmap(addr, size, prot, mmap_flags | MAP_FIXED,
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-1, 0);
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if (result == MAP_FAILED)
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return (true);
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if (result != addr) {
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@ -125,7 +146,6 @@ pages_commit_impl(void *addr, size_t size, bool commit)
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return (false);
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}
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#endif
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return (true);
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}
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bool
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@ -171,3 +191,63 @@ pages_purge(void *addr, size_t size)
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return (unzeroed);
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}
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#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
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static bool
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os_overcommits_sysctl(void)
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{
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int vm_overcommit;
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size_t sz;
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sz = sizeof(vm_overcommit);
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if (sysctlbyname("vm.overcommit", &vm_overcommit, &sz, NULL, 0) != 0)
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return (false); /* Error. */
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return ((vm_overcommit & 0x3) == 0);
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}
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#endif
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#ifdef JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY
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static bool
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os_overcommits_proc(void)
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{
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int fd;
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char buf[1];
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ssize_t nread;
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fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
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if (fd == -1)
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return (false); /* Error. */
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nread = read(fd, &buf, sizeof(buf));
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if (nread < 1)
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return (false); /* Error. */
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/*
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* /proc/sys/vm/overcommit_memory meanings:
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* 0: Heuristic overcommit.
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* 1: Always overcommit.
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* 2: Never overcommit.
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*/
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return (buf[0] == '0' || buf[0] == '1');
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}
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#endif
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void
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pages_boot(void)
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{
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#ifndef _WIN32
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mmap_flags = MAP_PRIVATE | MAP_ANON;
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#endif
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#ifdef JEMALLOC_SYSCTL_VM_OVERCOMMIT
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os_overcommits = os_overcommits_sysctl();
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#elif defined(JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY)
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os_overcommits = os_overcommits_proc();
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# ifdef MAP_NORESERVE
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if (os_overcommits)
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mmap_flags |= MAP_NORESERVE;
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# endif
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#else
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os_overcommits = false;
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#endif
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}
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