vmtouch - the Virtual Memory Toucher

https://hoytech.com/vmtouch/

[root@localhost ~]# git clone git://github.com/hoytech/vmtouch.git
正克隆到 'vmtouch'...
remote: Counting objects: 296, done.
remote: Total 296 (delta 0), reused 0 (delta 0), pack-reused 296
接收对象中: 100% (296/296), 285.79 KiB | 24.00 KiB/s, 完成.
处理 delta 中: 100% (144/144), 完成.
检查连接... 完成。
[root@localhost ~]# cd vmtouch
[root@localhost vmtouch]# make
cc -Wall -O2 -g -o vmtouch vmtouch.c
pod2man --section 8 --center "System Manager's Manual" --release " " vmtouch.pod > vmtouch.8

[root@localhost vmtouch]# make install
mkdir -p /usr/local/bin /usr/local/man/man8
install -m 0755 vmtouch /usr/local/bin/vmtouch
install -m 0644 vmtouch.8 /usr/local/man/man8/vmtouch.8
[root@localhost vmtouch]# /usr/local/bin/vmtouch
/usr/local/bin/vmtouch: no files or directories specified

vmtouch v1.0.2 - the Virtual Memory Toucher by Doug Hoyte
Portable file system cache diagnostics and control

Usage: vmtouch [OPTIONS] ... FILES OR DIRECTORIES ...

Options:
  -t touch pages into memory
  -e evict pages from memory
  -l lock pages in physical memory with mlock(2)
  -L lock pages in physical memory with mlockall(2)
  -d daemon mode
  -m <size> max file size to touch
  -p <range> use the specified portion instead of the entire file
  -f follow symbolic links
  -h also count hardlinked copies
  -w wait until all pages are locked (only useful together with -d)
  -v verbose
  -q quiet

vmtouch v1.0.2 - the Virtual Memory Toucher by Doug Hoyte
Portable file system cache diagnostics and control

Usage: vmtouch [OPTIONS] ... FILES OR DIRECTORIES ...

Options:
  -t touch pages into memory
  -e evict pages from memory
  -l lock pages in physical memory with mlock(2)
  -L lock pages in physical memory with mlockall(2)
  -d daemon mode
  -m <size> max file size to touch
  -p <range> use the specified portion instead of the entire file
  -f follow symbolic links
  -h also count hardlinked copies
  -w wait until all pages are locked (only useful together with -d)
  -v verbose
  -q quiet
[root@localhost vmtouch]# vmtouch -t /data
           Files: 193
     Directories: 7
   Touched Pages: 46138 (180M)
         Elapsed: 6.6931 seconds
[root@localhost vmtouch]# vmtouch -t /data/test/t.MYD
           Files: 1
     Directories: 0
   Touched Pages: 1 (4K)
         Elapsed: 0.000242 seconds
[root@localhost vmtouch]# vmtouch -e /data/test/t.MYD
           Files: 1
     Directories: 0
   Evicted Pages: 1 (4K)
         Elapsed: 7.7e-05 seconds
[root@localhost vmtouch]# vmtouch -e /data
           Files: 193
     Directories: 7
   Evicted Pages: 46138 (180M)
         Elapsed: 0.027778 seconds

[root@localhost vmtouch]# vmtouch -e /data/test/t.MYD -v
　　Evicting /data/test/t.MYD

　　Files: 1
　　Directories: 0
　　Evicted Pages: 1 (4K)
　　Elapsed: 0.000181 seconds

Portable file system cache diagnostics and control

• Download from github
• Read the online manual

vmtouch is a tool for learning about and controlling the file system cache of unix and unix-like systems. It is BSD licensed so you can basically do whatever you want with it.

Quick install guide:

$ git clone https://github.com/hoytech/vmtouch.git
$ cd vmtouch
$ make
$ sudo make install

What is it good for?

• Discovering which files your OS is caching
• Telling the OS to cache or evict certain files or regions of files
• Locking files into memory so the OS won't evict them
• Preserving virtual memory profile when failing over servers
• Keeping a "hot-standby" file-server
• Plotting filesystem cache usage over time
• Maintaining "soft quotas" of cache usage
• Speeding up batch/cron jobs
• And much more...

Examples

Example 1

How much of the /bin/ directory is currently in cache?

$ vmtouch /bin/
           Files: 92
     Directories: 1
  Resident Pages: 348/1307  1M/5M  26.6%
         Elapsed: 0.003426 seconds

Example 2

How much of big-dataset.txt is currently in memory?

$ vmtouch -v big-dataset.txt
big-dataset.txt
[                                                            ] 0/42116

           Files: 1
     Directories: 0
  Resident Pages: 0/42116  0/164M  0%
         Elapsed: 0.005182 seconds

None of it. Now let's bring part of it into memory with tail:

$ tail -n 10000 big-dataset.txt > /dev/null

Now how much?

$ vmtouch -v big-dataset.txt
big-dataset.txt
[                                                    oOOOOOOO] 4950/42116

           Files: 1
     Directories: 0
  Resident Pages: 4950/42116  19M/164M  11.8%
         Elapsed: 0.006706 seconds

vmtouch tells us that 4950 pages at the end of the file are now resident in memory.

Example 3

Let's touch the rest of /big-dataset.txt/ and bring it into memory (pressing enter a few times to illustrate the animated progress bar you will see on your terminal):

$ vmtouch -vt big-dataset.txt
big-dataset.txt
[OOo                                                 oOOOOOOO] 6887/42116
[OOOOOOOOo                                           oOOOOOOO] 10631/42116
[OOOOOOOOOOOOOOo                                     oOOOOOOO] 15351/42116
[OOOOOOOOOOOOOOOOOOOOOo                              oOOOOOOO] 19719/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOo                        oOOOOOOO] 24183/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo                  oOOOOOOO] 28615/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo              oOOOOOOO] 31415/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo      oOOOOOOO] 36775/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOo  oOOOOOOO] 39431/42116
[OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO] 42116/42116

           Files: 1
     Directories: 0
   Touched Pages: 42116 (164M)
         Elapsed: 12.107 seconds

Example 4

We have 3 big datasets, a.txt, b.txt, and c.txt but only 2 of them will fit in memory at once. If we have a.txtand b.txt in memory but would now like to work with b.txt and c.txt, we could just start loading up c.txt but then our system would evict pages from both a.txt (which we want) and b.txt (which we don't want).

So let's give the system a hint and evict a.txt from memory, making room for c.txt:

$ vmtouch -ve a.txt
Evicting a.txt

           Files: 1
     Directories: 0
   Evicted Pages: 42116 (164M)
         Elapsed: 0.076824 seconds

Example 5

Daemonise and lock all files in a directory into physical memory:

vmtouch -dl /var/www/htdocs/critical/

What other people are saying

People have found lots of uses for vmtouch over the years. Here are a few links in no particular order:

Articles

• Admin magazine: Performance Tuning Dojo: Tune-Up
• Techniques for Warming Up a MongoDB Secondary
• Linux Memory Usage
• What a C programmer should know about memory
• Playlists at Spotify - Using Cassandra to store version controlled objects (slide 32)
• Understanding and optimizing Memory utilization
• admon.org
• thewebdev.de
• Tune Up Paging with vmtouch
• Linux Cached Memory
• Of how much of a file is in RAM
• Manipulating the kernel's page cache with vmtouch
• Memory management in Linux kernel (slide 16)
• Supercomputing on the cheap with Parallella
• System Design and Big Data, chapter 6
• Lucene @ Yelp (slide 16)
• tuxdiary: vmtouch: portable file cache analyzer

Real-world sightings

• Linux kernel mailing list: zcache: Support zero-filled pages more efficiently
• comp.db.sqlite.general: Strange eviction from Linux page cache
• Emacs speed up 1000%
• Jolla Review: Some Rough Edges, But This Linux Smartphone Shows Promise (vmtouch deployed on maemo phones?)
• ceph-users: Ceph SSD array with Intel DC S3500's
• proxmox forums: CPU Performance Degradtion
• Argonne National Laboratory's Advanced Photon Source
• Elastic Search: Dealing with OS page cache evictions?
• Data-center deploy using torrent and mlock()
• Making best use of 512mb Pi with tmpfs
• redis-db: Issue with Redis replication while transferring rdb file from master to slave
• mongodb-user: Oplog Memory Consumption
• CentOS bugtracker: oom killer kills process rather than freeing cache

Instagram

Discussion about instagram's usage of vmtouch:

• What Powers Instagram: Hundreds of Instances, Dozens of Technologies
• Instagram Architecture: 14 Million Users, Terabytes Of Photos, 100s Of Instances, Dozens Of Technologies
• The Instagram Architecture Facebook Bought For A Cool Billion Dollars
• parse_vmtouch.py (script used by instagram)

Stack-overflow and friends

• Does the Linux filesystem cache files efficiently?
• Postgresql doesn't use memory for caching
• MongoDB, NUMA hardware, page faults
• Know programs in cache
• Is it possible to list the files that are cached?
• Tell the linux kernel to put a file in the disk cache?
• Securely wipe an entire Linux server with itself
• Caching/preloading files on Linux into RAM
• Why drop caches in Linux?
• Clear / Flush cached memory
• limit filesystem cache size for specific files under linux
• Memory mapping files for a blazing fast webserver on Linux
• Performance difference between ramfs and tmpfs
• How do I lock a growing directory in memory?
• How do I vmtouch a directory (not the files it contains)? (good question, I don't know of a userspace way to do this)
• MySQL queries are 10 to 100 times slower after OS reboot
• How can one examine what files are in Linux's page cache?

OS packages/ports

• Fedora Linux
• FreeBSD
• Debian (stalled)
• Arch Linux
• Gentoo Linux
• Ubuntu PPA

Non-english

• Spanish: 1
• French: 1 2
• Chinese: 1 2 3 4 5 6
• Russian: 1 2 3
• Polish: 1

Misc

• OpenHub
• Awesome C directory
• Computer Security Resources

Other tools

• linux-ftools
• cachemaster (inspired by vmtouch)
• pcstat
• fmlock
• nocache
• ureadahead

There are also lots of mentions on twitter using the #vmtouch hash-tag

Have another link? Please let me know!

Author

vmtouch is copyright (c) 2009-2016 Doug Hoyte and contributors.

Contributors are listed in CHANGES.