CODEWITHSUNDEEP
linuxcachingubunturam
dadexix86
dadexix86

Reputation: 215

Know programs in cache

I have this situation with RAM and SWAP at the moment:

$ free -h
             total       used       free     shared    buffers     cached
Mem:          7,7G       7,5G       159M       100M        75M       5,9G
-/+ buffers/cache:       1,5G       6,1G
Swap:         7,9G       408M       7,5G

And I was wondering...

Is there a way to know what programs/data are RAM-cached and/or from which process do they come from?

My idea is that, since they are re-usable, there should be a way to "identify" them.
But my knowledge is really too small to know how.

Thank you very much in advance.

Upvotes: 4

Views: 1068

Answers (1)

user184968
user184968

Reputation:

is there a way to know what programs/data are RAM-cached and/or from which process do they come from?

There is a program http://hoytech.com/vmtouch/ vmtouch. It gives information how much percent of a file in the file cache. You probably need to compile it. This is example on my computer:

Before reading a file which is not in the cache:

$ vmtouch -v  /usr/share/dict/linux.words
/usr/share/dict/linux.words
[                                                          ] 0/1210

           Files: 1
     Directories: 0
  Resident Pages: 0/1210  0/4M  0%
         Elapsed: 0.000169 seconds

After reading some data from the file:

$ tail -n 10000 /usr/share/dict/linux.words >/dev/null
$ vmtouch -v  /usr/share/dict/linux.words
/usr/share/dict/linux.words
[                                                        oO] 24/1210

           Files: 1
     Directories: 0
  Resident Pages: 24/1210  96K/4M  1.98%
         Elapsed: 0.000152 seconds

vmtouch frist calls nmap for a file and then uses mincore system call to determine if a file or some of its pages are resident in memory:

man mincore:

DESCRIPTION

mincore() returns a vector that indicates whether pages of the calling process’s virtual memory are resident in core (RAM), and so will not cause a disk access (page fault) if referenced. The kernel returns residency information about the pages starting at the address addr, and continuing for length bytes.

Upvotes: 2

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