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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import (
"runtime/internal/atomic"
"unsafe"
)
const (
_EACCES = 13
_EINVAL = 22
)
// Don't split the stack as this method may be invoked without a valid G, which
// prevents us from allocating more stack.
//go:nosplit
func sysAlloc(n uintptr, sysStat *sysMemStat) unsafe.Pointer {
p, err := mmap(nil, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
if err != 0 {
if err == _EACCES {
print("runtime: mmap: access denied\n")
exit(2)
}
if err == _EAGAIN {
print("runtime: mmap: too much locked memory (check 'ulimit -l').\n")
exit(2)
}
return nil
}
sysStat.add(int64(n))
return p
}
var adviseUnused = uint32(_MADV_FREE)
func sysUnused(v unsafe.Pointer, n uintptr) {
// By default, Linux's "transparent huge page" support will
// merge pages into a huge page if there's even a single
// present regular page, undoing the effects of madvise(adviseUnused)
// below. On amd64, that means khugepaged can turn a single
// 4KB page to 2MB, bloating the process's RSS by as much as
// 512X. (See issue #8832 and Linux kernel bug
// https://bugzilla.kernel.org/show_bug.cgi?id=93111)
//
// To work around this, we explicitly disable transparent huge
// pages when we release pages of the heap. However, we have
// to do this carefully because changing this flag tends to
// split the VMA (memory mapping) containing v in to three
// VMAs in order to track the different values of the
// MADV_NOHUGEPAGE flag in the different regions. There's a
// default limit of 65530 VMAs per address space (sysctl
// vm.max_map_count), so we must be careful not to create too
// many VMAs (see issue #12233).
//
// Since huge pages are huge, there's little use in adjusting
// the MADV_NOHUGEPAGE flag on a fine granularity, so we avoid
// exploding the number of VMAs by only adjusting the
// MADV_NOHUGEPAGE flag on a large granularity. This still
// gets most of the benefit of huge pages while keeping the
// number of VMAs under control. With hugePageSize = 2MB, even
// a pessimal heap can reach 128GB before running out of VMAs.
if physHugePageSize != 0 {
// If it's a large allocation, we want to leave huge
// pages enabled. Hence, we only adjust the huge page
// flag on the huge pages containing v and v+n-1, and
// only if those aren't aligned.
var head, tail uintptr
if uintptr(v)&(physHugePageSize-1) != 0 {
// Compute huge page containing v.
head = alignDown(uintptr(v), physHugePageSize)
}
if (uintptr(v)+n)&(physHugePageSize-1) != 0 {
// Compute huge page containing v+n-1.
tail = alignDown(uintptr(v)+n-1, physHugePageSize)
}
// Note that madvise will return EINVAL if the flag is
// already set, which is quite likely. We ignore
// errors.
if head != 0 && head+physHugePageSize == tail {
// head and tail are different but adjacent,
// so do this in one call.
madvise(unsafe.Pointer(head), 2*physHugePageSize, _MADV_NOHUGEPAGE)
} else {
// Advise the huge pages containing v and v+n-1.
if head != 0 {
madvise(unsafe.Pointer(head), physHugePageSize, _MADV_NOHUGEPAGE)
}
if tail != 0 && tail != head {
madvise(unsafe.Pointer(tail), physHugePageSize, _MADV_NOHUGEPAGE)
}
}
}
if uintptr(v)&(physPageSize-1) != 0 || n&(physPageSize-1) != 0 {
// madvise will round this to any physical page
// *covered* by this range, so an unaligned madvise
// will release more memory than intended.
throw("unaligned sysUnused")
}
var advise uint32
if debug.madvdontneed != 0 {
advise = _MADV_DONTNEED
} else {
advise = atomic.Load(&adviseUnused)
}
if errno := madvise(v, n, int32(advise)); advise == _MADV_FREE && errno != 0 {
// MADV_FREE was added in Linux 4.5. Fall back to MADV_DONTNEED if it is
// not supported.
atomic.Store(&adviseUnused, _MADV_DONTNEED)
madvise(v, n, _MADV_DONTNEED)
}
}
func sysUsed(v unsafe.Pointer, n uintptr) {
// Partially undo the NOHUGEPAGE marks from sysUnused
// for whole huge pages between v and v+n. This may
// leave huge pages off at the end points v and v+n
// even though allocations may cover these entire huge
// pages. We could detect this and undo NOHUGEPAGE on
// the end points as well, but it's probably not worth
// the cost because when neighboring allocations are
// freed sysUnused will just set NOHUGEPAGE again.
sysHugePage(v, n)
}
func sysHugePage(v unsafe.Pointer, n uintptr) {
if physHugePageSize != 0 {
// Round v up to a huge page boundary.
beg := alignUp(uintptr(v), physHugePageSize)
// Round v+n down to a huge page boundary.
end := alignDown(uintptr(v)+n, physHugePageSize)
if beg < end {
madvise(unsafe.Pointer(beg), end-beg, _MADV_HUGEPAGE)
}
}
}
// Don't split the stack as this function may be invoked without a valid G,
// which prevents us from allocating more stack.
//go:nosplit
func sysFree(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
sysStat.add(-int64(n))
munmap(v, n)
}
func sysFault(v unsafe.Pointer, n uintptr) {
mmap(v, n, _PROT_NONE, _MAP_ANON|_MAP_PRIVATE|_MAP_FIXED, -1, 0)
}
func sysReserve(v unsafe.Pointer, n uintptr) unsafe.Pointer {
p, err := mmap(v, n, _PROT_NONE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
if err != 0 {
return nil
}
return p
}
func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
sysStat.add(int64(n))
p, err := mmap(v, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE, -1, 0)
if err == _ENOMEM {
throw("runtime: out of memory")
}
if p != v || err != 0 {
throw("runtime: cannot map pages in arena address space")
}
}
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