├── .gitignore ├── LICENSE ├── README.md ├── lru ├── go.mod └── main.go ├── mincore ├── go.mod └── main.go └── uss ├── go.mod └── main.go /.gitignore: -------------------------------------------------------------------------------- 1 | # Byte-compiled / optimized / DLL files 2 | __pycache__/ 3 | *.py[cod] 4 | *$py.class 5 | 6 | # C extensions 7 | *.so 8 | 9 | # Distribution / packaging 10 | .Python 11 | build/ 12 | develop-eggs/ 13 | dist/ 14 | downloads/ 15 | eggs/ 16 | .eggs/ 17 | lib/ 18 | lib64/ 19 | parts/ 20 | sdist/ 21 | var/ 22 | wheels/ 23 | pip-wheel-metadata/ 24 | share/python-wheels/ 25 | *.egg-info/ 26 | .installed.cfg 27 | *.egg 28 | MANIFEST 29 | 30 | # PyInstaller 31 | # Usually these files are written by a python script from a template 32 | # before PyInstaller builds the exe, so as to inject date/other infos into it. 33 | *.manifest 34 | *.spec 35 | 36 | # Installer logs 37 | pip-log.txt 38 | pip-delete-this-directory.txt 39 | 40 | # Unit test / coverage reports 41 | htmlcov/ 42 | .tox/ 43 | .nox/ 44 | .coverage 45 | .coverage.* 46 | .cache 47 | nosetests.xml 48 | coverage.xml 49 | *.cover 50 | *.py,cover 51 | .hypothesis/ 52 | .pytest_cache/ 53 | 54 | # Translations 55 | *.mo 56 | *.pot 57 | 58 | # Django stuff: 59 | *.log 60 | local_settings.py 61 | db.sqlite3 62 | db.sqlite3-journal 63 | 64 | # Flask stuff: 65 | instance/ 66 | .webassets-cache 67 | 68 | # Scrapy stuff: 69 | .scrapy 70 | 71 | # Sphinx documentation 72 | docs/_build/ 73 | 74 | # PyBuilder 75 | target/ 76 | 77 | # Jupyter Notebook 78 | .ipynb_checkpoints 79 | 80 | # IPython 81 | profile_default/ 82 | ipython_config.py 83 | 84 | # pyenv 85 | .python-version 86 | 87 | # pipenv 88 | # According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control. 89 | # However, in case of collaboration, if having platform-specific dependencies or dependencies 90 | # having no cross-platform support, pipenv may install dependencies that don't work, or not 91 | # install all needed dependencies. 92 | #Pipfile.lock 93 | 94 | # PEP 582; used by e.g. github.com/David-OConnor/pyflow 95 | __pypackages__/ 96 | 97 | # Celery stuff 98 | celerybeat-schedule 99 | celerybeat.pid 100 | 101 | # SageMath parsed files 102 | *.sage.py 103 | 104 | # Environments 105 | .env 106 | .venv 107 | env/ 108 | venv/ 109 | ENV/ 110 | env.bak/ 111 | venv.bak/ 112 | 113 | # Spyder project settings 114 | .spyderproject 115 | .spyproject 116 | 117 | # Rope project settings 118 | .ropeproject 119 | 120 | # mkdocs documentation 121 | /site 122 | 123 | # mypy 124 | .mypy_cache/ 125 | .dmypy.json 126 | dmypy.json 127 | 128 | # Pyre type checker 129 | .pyre/ 130 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright [yyyy] [name of copyright owner] 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Code examples 2 | 3 | ## `mincore()` example 4 | 5 | See `mincore` folder. 6 | 7 | ## Unique set size example 8 | 9 | See `uss` folder. 10 | 11 | ## Active and Inective LRU lists content for a file 12 | 13 | See `lru` folder. 14 | -------------------------------------------------------------------------------- /lru/go.mod: -------------------------------------------------------------------------------- 1 | module github.com/brk0v/sre-page-cache-article/lru 2 | 3 | go 1.17 4 | -------------------------------------------------------------------------------- /lru/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "encoding/binary" 5 | "fmt" 6 | "log" 7 | "os" 8 | "syscall" 9 | "unsafe" 10 | ) 11 | 12 | const ( 13 | PAGEMAP_LENGTH = int64(8) 14 | PFN_MASK = 0x7FFFFFFFFFFFFF 15 | PAGEMAP_BATCH = 64 << 10 16 | 17 | //https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/kernel-page-flags.h 18 | KPF_LRU = 1 << 5 19 | KPF_ACTIVE = 1 << 6 20 | ) 21 | 22 | var ( 23 | pageSize = int64(syscall.Getpagesize()) 24 | mode = os.FileMode(0600) 25 | ) 26 | 27 | func main() { 28 | pagemap, err := os.OpenFile("/proc/self/pagemap", os.O_RDONLY, mode) 29 | if err != nil { 30 | log.Fatal(err) 31 | } 32 | 33 | kpageflags, err := os.OpenFile("/proc/kpageflags", os.O_RDONLY, mode) 34 | if err != nil { 35 | log.Fatal(err) 36 | } 37 | 38 | path := "/var/tmp/file1.db" 39 | 40 | file, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_NOATIME, mode) 41 | if err != nil { 42 | log.Fatal(err) 43 | } 44 | defer file.Close() 45 | 46 | stat, err := os.Lstat(path) 47 | if err != nil { 48 | log.Fatal(err) 49 | } 50 | size := stat.Size() 51 | pages := size / pageSize 52 | 53 | // Not 100% correct code because the size could be bigger than int, don't use for production code 54 | mm, err := syscall.Mmap(int(file.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_SHARED) 55 | defer syscall.Munmap(mm) 56 | 57 | // Turn off the read ahead logic because we don't need to read more data in Page Cache 58 | err = syscall.Madvise(mm, syscall.MADV_RANDOM) 59 | if err != nil { 60 | log.Fatal(err) 61 | } 62 | 63 | mmPtr := uintptr(unsafe.Pointer(&mm[0])) 64 | cached := make([]byte, pages) 65 | 66 | sizePtr := uintptr(size) 67 | cachedPtr := uintptr(unsafe.Pointer(&cached[0])) 68 | 69 | ret, _, err := syscall.Syscall(syscall.SYS_MINCORE, mmPtr, sizePtr, cachedPtr) 70 | if ret != 0 { 71 | log.Fatal("syscall SYS_MINCORE failed: %v", err) 72 | } 73 | 74 | for i, p := range cached { 75 | // If page in Page Cache we need to populate the page table off the current 76 | // process wit entries. We are doing thi with a hack to bypass golang optimizations. 77 | if p%2 == 1 { 78 | _ = *(*int)(unsafe.Pointer(mmPtr + uintptr(pageSize*int64(i)))) 79 | } 80 | } 81 | 82 | // this is a hach wich we need to notify kernel to not update reference bits 83 | err = syscall.Madvise(mm, syscall.MADV_SEQUENTIAL) 84 | if err != nil { 85 | log.Fatal(err) 86 | } 87 | 88 | active := int64(0) 89 | inactive := int64(0) 90 | for i := int64(0); i < pages; i++ { 91 | offset := ((int64(mmPtr) + i*pageSize) / pageSize) * PAGEMAP_LENGTH 92 | buf := make([]byte, int(PAGEMAP_LENGTH)) 93 | 94 | _, err := pagemap.ReadAt(buf, offset) 95 | if err != nil { 96 | log.Fatal(err) 97 | } 98 | 99 | pfn := binary.LittleEndian.Uint64(buf) & PFN_MASK 100 | if pfn == 0 { 101 | continue 102 | } 103 | 104 | _, err = kpageflags.ReadAt(buf, int64(pfn)*PAGEMAP_LENGTH) 105 | if err != nil { 106 | log.Fatal(err) 107 | } 108 | flags := binary.LittleEndian.Uint64(buf) 109 | 110 | if flags&KPF_ACTIVE != 0 { 111 | active += 1 112 | continue 113 | } 114 | 115 | if flags&KPF_LRU != 0 { 116 | inactive += 1 117 | } 118 | } 119 | fmt.Printf(" Size\t\t\tPages\n") 120 | fmt.Printf("File: %d\t\t\t%d\n", size, pages) 121 | fmt.Printf("Active: %d\t\t\t%d\n", active*pageSize, active) 122 | fmt.Printf("Inactive: %d\t\t\t%d\n", inactive*pageSize, inactive) 123 | fmt.Printf("Not charged: %d\t\t\t%d\n", size-inactive*pageSize+active*pageSize, pages-active-inactive) 124 | } 125 | -------------------------------------------------------------------------------- /mincore/go.mod: -------------------------------------------------------------------------------- 1 | module github.com/brk0v/sre-page-cache-article/mincore 2 | 3 | go 1.17 4 | -------------------------------------------------------------------------------- /mincore/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "log" 6 | "os" 7 | "syscall" 8 | "unsafe" 9 | ) 10 | 11 | var ( 12 | pageSize = int64(syscall.Getpagesize()) 13 | mode = os.FileMode(0600) 14 | ) 15 | 16 | func main() { 17 | path := "/var/tmp/file1.db" 18 | 19 | file, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_NOATIME, mode) 20 | if err != nil { 21 | log.Fatal(err) 22 | } 23 | defer file.Close() 24 | 25 | stat, err := os.Lstat(path) 26 | if err != nil { 27 | log.Fatal(err) 28 | } 29 | size := stat.Size() 30 | pages := size / pageSize 31 | 32 | mm, err := syscall.Mmap(int(file.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_SHARED) 33 | defer syscall.Munmap(mm) 34 | 35 | mmPtr := uintptr(unsafe.Pointer(&mm[0])) 36 | cached := make([]byte, pages) 37 | 38 | sizePtr := uintptr(size) 39 | cachedPtr := uintptr(unsafe.Pointer(&cached[0])) 40 | 41 | ret, _, err := syscall.Syscall(syscall.SYS_MINCORE, mmPtr, sizePtr, cachedPtr) 42 | if ret != 0 { 43 | log.Fatal("syscall SYS_MINCORE failed: %v", err) 44 | } 45 | 46 | n := 0 47 | for _, p := range cached { 48 | if p%2 == 1 { 49 | n++ 50 | } 51 | } 52 | 53 | fmt.Printf("Resident Pages: %d/%d %d/%d\n", n, pages, n*int(pageSize), size) 54 | } 55 | -------------------------------------------------------------------------------- /uss/go.mod: -------------------------------------------------------------------------------- 1 | module github.com/brk0v/sre-page-cache-article/uss 2 | 3 | go 1.17 4 | -------------------------------------------------------------------------------- /uss/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "bufio" 5 | "encoding/binary" 6 | "fmt" 7 | "log" 8 | "os" 9 | "strconv" 10 | "strings" 11 | "syscall" 12 | ) 13 | 14 | const ( 15 | PAGEMAP_LENGTH = int64(8) 16 | PFN_MASK = 0x7FFFFFFFFFFFFF 17 | PAGEMAP_BATCH = 64 << 10 18 | ) 19 | 20 | var ( 21 | pageSize = int64(syscall.Getpagesize()) 22 | mode = os.FileMode(0600) 23 | ) 24 | 25 | func main() { 26 | pid := os.Args[1] 27 | 28 | pagemap, err := os.OpenFile(fmt.Sprintf("/proc/%s/pagemap", pid), os.O_RDONLY, mode) 29 | if err != nil { 30 | log.Fatal(err) 31 | } 32 | 33 | kpagecount, err := os.OpenFile("/proc/kpagecount", os.O_RDONLY, mode) 34 | if err != nil { 35 | log.Fatal(err) 36 | } 37 | 38 | maps, err := os.Open(fmt.Sprintf("/proc/%s/maps", pid)) 39 | if err != nil { 40 | log.Fatal(err) 41 | } 42 | 43 | pages := make(map[int64]int64) 44 | 45 | scanner := bufio.NewScanner(maps) 46 | for scanner.Scan() { 47 | line := scanner.Text() 48 | info := strings.Fields(line) 49 | if len(info) == 6 && info[5] == "[vsyscall]" { 50 | continue 51 | } 52 | s := strings.Split(info[0], "-") 53 | startHex, endHex := s[0], s[1] 54 | start, err := strconv.ParseInt(startHex, 16, 64) 55 | if err != nil { 56 | log.Fatal(err) 57 | } 58 | end, err := strconv.ParseInt(endHex, 16, 64) 59 | if err != nil { 60 | log.Fatal(err) 61 | } 62 | pages[start/pageSize] = end / pageSize 63 | } 64 | 65 | uss := 0 66 | already := make(map[int64]struct{}) // don't count same addresses twice 67 | 68 | for start, end := range pages { 69 | for i := start; i <= end; i++ { 70 | offset := i * PAGEMAP_LENGTH 71 | if _, ok := already[offset]; ok { 72 | continue 73 | } 74 | 75 | buf := make([]byte, int(PAGEMAP_LENGTH)) 76 | _, err := pagemap.ReadAt(buf, offset) 77 | if err != nil { 78 | log.Fatal(err) 79 | } 80 | 81 | pfn := binary.LittleEndian.Uint64(buf) & PFN_MASK 82 | if pfn == 0 { 83 | continue 84 | } 85 | 86 | _, err = kpagecount.ReadAt(buf, int64(pfn)*PAGEMAP_LENGTH) 87 | if err != nil { 88 | log.Fatal(err) 89 | } 90 | count := binary.LittleEndian.Uint64(buf) 91 | if count == 1 { 92 | uss++ 93 | } 94 | already[offset] = struct{}{} 95 | } 96 | } 97 | fmt.Println(uss) 98 | } 99 | --------------------------------------------------------------------------------