improve commit/decommit on Linux
@@ -889,8 +889,7 @@ static bool mi_os_commitx(void* addr, size_t size, bool commit, bool conservativ
#if defined(_WIN32)
if (commit) {
- // if the memory was already committed, the call succeeds but it is not zero'd
- // *is_zero = true;
+ // *is_zero = true; // note: if the memory was already committed, the call succeeds but the memory is not zero'd
void* p = VirtualAlloc(start, csize, MEM_COMMIT, PAGE_READWRITE);
err = (p == start ? 0 : GetLastError());
}
@@ -900,23 +899,40 @@ static bool mi_os_commitx(void* addr, size_t size, bool commit, bool conservativ
}
#elif defined(__wasi__)
// WebAssembly guests can't control memory protection
- #elif defined(MAP_FIXED)
- if (!commit) {
- // use mmap with MAP_FIXED to discard the existing memory (and reduce commit charge)
- void* p = mmap(start, csize, PROT_NONE, (MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE), -1, 0);
- if (p != start) { err = errno; }
+ #elif 0 && defined(MAP_FIXED) && !defined(__APPLE__)
+ // Linux: disabled for now as mmap fixed seems much more expensive than MADV_DONTNEED (and splits VMA's?)
+ if (commit) {
+ // commit: just change the protection
+ err = mprotect(start, csize, (PROT_READ | PROT_WRITE));
+ if (err != 0) { err = errno; }
}
else {
- // for commit, just change the protection
+ // decommit: use mmap with MAP_FIXED to discard the existing memory (and reduce rss)
+ const int fd = mi_unix_mmap_fd();
+ void* p = mmap(start, csize, PROT_NONE, (MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE), fd, 0);
+ if (p != start) { err = errno; }
+ }
+ #else
+ // Linux, macOSX and others.
+ if (commit) {
+ // commit: ensure we can access the area
err = mprotect(start, csize, (PROT_READ | PROT_WRITE));
if (err != 0) { err = errno; }
+ }
+ else {
+ #if defined(MADV_DONTNEED) && MI_DEBUG == 0 && MI_SECURE == 0
+ // decommit: use MADV_DONTNEED as it decreases rss immediately (unlike MADV_FREE)
+ // (on the other hand, MADV_FREE would be good enough.. it is just not reflected in the stats :-( )
+ err = madvise(start, csize, MADV_DONTNEED);
+ #else
+ // decommit: just disable access (also used in debug and secure mode to trap on illegal access)
+ err = mprotect(start, csize, PROT_NONE);
+ if (err != 0) { err = errno; }
+ #endif
//#if defined(MADV_FREE_REUSE)
// while ((err = mi_madvise(start, csize, MADV_FREE_REUSE)) != 0 && errno == EAGAIN) { errno = 0; }
//#endif
}
- #else
- err = mprotect(start, csize, (commit ? (PROT_READ | PROT_WRITE) : PROT_NONE));
- if (err != 0) { err = errno; }
#endif
if (err != 0) {
_mi_warning_message("%s error: start: %p, csize: 0x%zx, err: %i\n", commit ? "commit" : "decommit", start, csize, err);
