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San: Implement bump alloc

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The new allocator will be used to allocate guarded extents used as slabs
for guarded small allocations.
This commit is contained in:
Alex Lapenkou 2021-11-04 11:10:19 -07:00 • committed by Alexander Lapenkov
parent 34b00f8969
commit 0f6da1257d
15 changed files with 521 additions and 107 deletions
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56
src/pages.c
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@ -365,33 +365,61 @@ pages_decommit(void *addr, size_t size) {
void
pages_mark_guards(void *head, void *tail) {
assert(head != NULL && tail != NULL);
assert((uintptr_t)head < (uintptr_t)tail);
assert(head != NULL || tail != NULL);
assert(head == NULL || tail == NULL ||
(uintptr_t)head < (uintptr_t)tail);
#ifdef JEMALLOC_HAVE_MPROTECT
mprotect(head, PAGE, PROT_NONE);
mprotect(tail, PAGE, PROT_NONE);
if (head != NULL) {
mprotect(head, PAGE, PROT_NONE);
}
if (tail != NULL) {
mprotect(tail, PAGE, PROT_NONE);
}
#else
/* Decommit sets to PROT_NONE / MEM_DECOMMIT. */
os_pages_commit(head, PAGE, false);
os_pages_commit(tail, PAGE, false);
if (head != NULL) {
os_pages_commit(head, PAGE, false);
}
if (tail != NULL) {
os_pages_commit(tail, PAGE, false);
}
#endif
}
void
pages_unmark_guards(void *head, void *tail) {
assert(head != NULL && tail != NULL);
assert((uintptr_t)head < (uintptr_t)tail);
assert(head != NULL || tail != NULL);
assert(head == NULL || tail == NULL ||
(uintptr_t)head < (uintptr_t)tail);
#ifdef JEMALLOC_HAVE_MPROTECT
size_t range = (uintptr_t)tail - (uintptr_t)head + PAGE;
if (range <= SC_LARGE_MINCLASS) {
bool head_and_tail = (head != NULL) && (tail != NULL);
size_t range = head_and_tail ?
(uintptr_t)tail - (uintptr_t)head + PAGE :
SIZE_T_MAX;
/*
* The amount of work that the kernel does in mprotect depends on the
* range argument. SC_LARGE_MINCLASS is an arbitrary threshold chosen
* to prevent kernel from doing too much work that would outweigh the
* savings of performing one less system call.
*/
bool ranged_mprotect = head_and_tail && range <= SC_LARGE_MINCLASS;
if (ranged_mprotect) {
mprotect(head, range, PROT_READ | PROT_WRITE);
} else {
mprotect(head, PAGE, PROT_READ | PROT_WRITE);
mprotect(tail, PAGE, PROT_READ | PROT_WRITE);
if (head != NULL) {
mprotect(head, PAGE, PROT_READ | PROT_WRITE);
}
if (tail != NULL) {
mprotect(tail, PAGE, PROT_READ | PROT_WRITE);
}
}
#else
os_pages_commit(head, PAGE, true);
os_pages_commit(tail, PAGE, true);
if (head != NULL) {
os_pages_commit(head, PAGE, true);
}
if (tail != NULL) {
os_pages_commit(tail, PAGE, true);
}
#endif
}