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improve commit/decommit on Linux

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This commit is contained in:
Daan Leijen 2022-01-10 15:39:49 -08:00
parent 8c50aa65ee
commit 807a7ff08d
1 changed files with 29 additions and 13 deletions
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42
src/os.c
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@ -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; }
}
else {
// for commit, just change the protection
#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 {
// 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);