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use MADV_DONTNEED instead of mmap fixedfor simplification and possibly better performance on Linux

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This commit is contained in:
Daan 2021-10-19 13:18:54 -07:00
commit 35b928b08f
1 changed files with 8 additions and 15 deletions
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23
src/os.c
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@ -782,8 +782,8 @@ 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) && !defined(__APPLE__)
// Linux
#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));
@ -796,23 +796,21 @@ static bool mi_os_commitx(void* addr, size_t size, bool commit, bool conservativ
if (p != start) { err = errno; }
}
#else
// macOSX and others.
// Linux, macOSX and others.
if (commit) {
// commit: ensure we can access the area
// 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)
// 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
err = mprotect(start, csize, PROT_NONE);
if (err != 0) { err = errno; }
#if defined(MADV_FREE_REUSE)
while ((err = madvise(start, csize, MADV_FREE_REUSE)) != 0 && errno == EAGAIN) { errno = 0; }
#endif
#endif
}
#endif
@ -872,17 +870,12 @@ static bool mi_os_resetx(void* addr, size_t size, bool reset, mi_stats_t* stats)
if (p != start) return false;
#else
#if defined(MADV_FREE)
#if defined(MADV_FREE_REUSABLE)
#define KK_MADV_FREE_INITIAL MADV_FREE_REUSABLE
#else
#define KK_MADV_FREE_INITIAL MADV_FREE
#endif
static _Atomic(uintptr_t) advice = ATOMIC_VAR_INIT(KK_MADV_FREE_INITIAL);
static _Atomic(uintptr_t) advice = ATOMIC_VAR_INIT(MADV_FREE);
int oadvice = (int)mi_atomic_load_relaxed(&advice);
int err;
while ((err = madvise(start, csize, oadvice)) != 0 && errno == EAGAIN) { errno = 0; };
if (err != 0 && errno == EINVAL && oadvice == KK_MADV_FREE_INITIAL) {
// if MADV_FREE/MADV_FREE_REUSABLE is not supported, fall back to MADV_DONTNEED from now on
if (err != 0 && errno == EINVAL && oadvice == MADV_FREE) {
// if MADV_FREE is not supported, fall back to MADV_DONTNEED from now on
mi_atomic_store_release(&advice, (uintptr_t)MADV_DONTNEED);
err = madvise(start, csize, MADV_DONTNEED);
}