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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "berberis/base/memfd_backed_mmap.h"
#include <sys/mman.h>
#include <unistd.h>
#include "berberis/base/fd.h"
#include "berberis/base/large_mmap.h"
#include "berberis/base/logging.h"
#include "berberis/base/mmap.h"
namespace berberis {
// Creates memfd region of memfd_file_size bytes filled with value.
int CreateAndFillMemfd(const char* name, size_t memfd_file_size, uintptr_t value) {
const size_t kPageSize = sysconf(_SC_PAGE_SIZE);
CHECK_EQ(memfd_file_size % sizeof(value), 0);
CHECK_EQ(memfd_file_size % kPageSize, 0);
// Use intermediate map to fully initialize file content. It lets compiler
// optimize the loop below and limits WriteFully to fd to one call. Running
// the Memfd.uintptr_t test on this showed 4x performance improvement.
uintptr_t* memfd_file_content = static_cast<uintptr_t*>(MmapOrDie(memfd_file_size));
for (size_t i = 0; i < memfd_file_size / sizeof(value); ++i) {
memfd_file_content[i] = value;
}
int memfd = CreateMemfdOrDie(name);
WriteFullyOrDie(memfd, memfd_file_content, memfd_file_size);
MunmapOrDie(memfd_file_content, memfd_file_size);
return memfd;
}
// Allocates a region of map_size bytes and backs it in chunks with memfd region
// of memfd_file_size bytes.
void* CreateMemfdBackedMapOrDie(int memfd, size_t map_size, size_t memfd_file_size) {
const size_t kPageSize = sysconf(_SC_PAGE_SIZE);
CHECK_EQ(map_size % memfd_file_size, 0);
CHECK_EQ(memfd_file_size % kPageSize, 0);
// Reserving memory for the map. Instruct kernel to not commit any RAM to
// the map by using MAP_NORESERVE. It would be a waste anyways since
// this region is used to create memfd backed mmaps.
uint8_t* ptr = static_cast<uint8_t*>(
LargeMmapImplOrDie({.size = map_size, .flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE}));
// map memfd
for (size_t i = 0; i < map_size / memfd_file_size; ++i) {
MmapImplOrDie({.addr = ptr + (i * memfd_file_size),
.size = memfd_file_size,
.flags = MAP_PRIVATE | MAP_FIXED,
.fd = memfd});
}
return ptr;
}
} // namespace berberis
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