github.com/dgraph-io/ristretto@v0.1.2-0.20240116140435-c67e07994f91/z/mremap_nosize.go (about)

     1  //go:build (arm64 || arm) && linux
     2  // +build arm64 arm
     3  // +build linux
     4  
     5  /*
     6   * Copyright 2020 Dgraph Labs, Inc. and Contributors
     7   *
     8   * Licensed under the Apache License, Version 2.0 (the "License");
     9   * you may not use this file except in compliance with the License.
    10   * You may obtain a copy of the License at
    11   *
    12   *     http://www.apache.org/licenses/LICENSE-2.0
    13   *
    14   * Unless required by applicable law or agreed to in writing, software
    15   * distributed under the License is distributed on an "AS IS" BASIS,
    16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    17   * See the License for the specific language governing permissions and
    18   * limitations under the License.
    19   */
    20  
    21  package z
    22  
    23  import (
    24  	"reflect"
    25  	"unsafe"
    26  
    27  	"golang.org/x/sys/unix"
    28  )
    29  
    30  // mremap is a Linux-specific system call to remap pages in memory. This can be used in place of munmap + mmap.
    31  func mremap(data []byte, size int) ([]byte, error) {
    32  	//nolint:lll
    33  	// taken from <https://github.com/torvalds/linux/blob/f8394f232b1eab649ce2df5c5f15b0e528c92091/include/uapi/linux/mman.h#L8>
    34  	const MREMAP_MAYMOVE = 0x1
    35  
    36  	header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
    37  	// For ARM64, the second return argument for SYS_MREMAP is inconsistent (prior allocated size) with
    38  	// other architectures, which return the size allocated
    39  	mmapAddr, _, errno := unix.Syscall6(
    40  		unix.SYS_MREMAP,
    41  		header.Data,
    42  		uintptr(header.Len),
    43  		uintptr(size),
    44  		uintptr(MREMAP_MAYMOVE),
    45  		0,
    46  		0,
    47  	)
    48  	if errno != 0 {
    49  		return nil, errno
    50  	}
    51  
    52  	header.Data = mmapAddr
    53  	header.Cap = size
    54  	header.Len = size
    55  	return data, nil
    56  }