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Make realloc() go 100x faster on Linux/NetBSD

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Cosmopolitan now supports mremap(), which is only supported on Linux and
NetBSD. First, it allows memory mappings to be relocated without copying
them; this can dramatically speed up data structures like std::vector if
the array size grows larger than 256kb. The mremap() system call is also
10x faster than munmap() when shrinking large memory mappings.

There's now two functions, getpagesize() and getgransize() which help to
write portable code that uses mmap(MAP_FIXED). Alternative sysconf() may
be called with our new _SC_GRANSIZE. The madvise() system call now has a
better wrapper with improved documentation.
This commit is contained in:
Justine Tunney 2024-07-07 12:24:25 -07:00
parent 196942084b
commit f7780de24b
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GPG key ID: BE714B4575D6E328
71 changed files with 1301 additions and 640 deletions
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42
libc/calls/madvise.c
View file

@ -21,27 +21,49 @@
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
#include "libc/intrin/strace.internal.h"
#include "libc/runtime/runtime.h"
#include "libc/sysv/errfuns.h"
static int __madvise(void *addr, size_t length, int advice) {
// simulate linux behavior of validating alignment
if ((uintptr_t)addr & (getpagesize() - 1))
return einval();
// simulate linux behavior of checking for negative length
if ((ssize_t)length < 0)
return einval();
// madvise(0, 0, advice) may be used to validate advice
if (!length && (IsFreebsd() || IsNetbsd()))
addr = (void *)65536l;
if (!IsWindows())
return sys_madvise(addr, length, advice);
return sys_madvise_nt(addr, length, advice);
}
/**
* Drops hints to O/S about intended access patterns of mmap()'d memory.
* Declares intent to OS on how memory region will be used.
*
* `madvise(0, 0, advice)` is recommended for validating `advise` and it
* will always be the case that a `length` of zero is a no-op otherwise.
*
* Having the interval overlap unmapped pages has undefined behavior. On
* Linux, this can be counted upon to raise ENOMEM. Other OSes vary much
* in behavior here; they'll might ignore unmapped regions or they might
* raise EINVAL, EFAULT, or ENOMEM.
*
* @param advice can be MADV_WILLNEED, MADV_SEQUENTIAL, MADV_FREE, etc.
* @return 0 on success, or -1 w/ errno
* @raise EINVAL if `advice` isn't valid or supported by system
* @raise EINVAL on Linux if addr/length isn't page size aligned with
* respect to `getpagesize()`
* @raise ENOMEM on Linux if addr/length overlaps unmapped regions
* @raise EINVAL if `addr` isn't getpagesize() aligned
* @raise EINVAL if `length` is negative
* @see libc/sysv/consts.sh
* @see fadvise()
*/
int madvise(void *addr, size_t length, int advice) {
int rc;
if (!IsWindows()) {
rc = sys_madvise(addr, length, advice);
} else {
rc = sys_madvise_nt(addr, length, advice);
}
int rc = __madvise(addr, length, advice);
STRACE("madvise(%p, %'zu, %d) → %d% m", addr, length, advice, rc);
return rc;
}