Re: Memory usage Debian Jessie (stable)
On 05/12/2015 04:33 AM, Fabio Tobich wrote:
You can drop the cache with this command:
sync; echo 3 > /proc/sys/vm/drop_caches
See what it does at my laptop:
root@laptop:~# free -m
total used free shared buffers
cached
Mem: 7439 3029 4409 201 91 1368
-/+ buffers/cache: 1569 5870
Swap: 1906 0 1906
root@laptop:~# sync; echo 3 > /proc/sys/vm/drop_caches
root@laptop:~# free -m
total used free shared buffers
cached
Mem: 7439 2001 5437 194 2 480
-/+ buffers/cache: 1518 5920
Swap: 1906 0 1906
As you can see, the cache was reduced from 1368 to 480, "freeing" more
than 1GB, but on the second line the free ammount remains the same
because, as Dan said, it ignores the cache.
In
$ man proc
I read:
/proc/sys/vm/drop_caches (since Linux 2.6.16)
Writing to this file causes the kernel to drop clean caches,
dentries, and inodes from memory, causing that memory to
become free. This can be useful for memory management testing
and performing reproducible filesystem benchmarks. Because
writing to this file causes the benefits of caching to be lost,
it can degrade overall system performance.
So dropping caches may increase the amount of overhead.
2015-05-11 11:50 GMT-03:00 Dan Christensen <jdc@uwo.ca <mailto:jdc@uwo.ca>>:
Jan-Rens Reitsma <jan.rens.reitsma@gmail.com
<mailto:jan.rens.reitsma@gmail.com>> writes:
> $ free -h
> total used free shared buffers
cached
> Mem: 3.7G 3.5G 182M 153M 363M
2.1G
> -/+ buffers/cache: 1.0G 2.7G
> Swap: 7.6G 0B 7.6G
>
> 3.5 GB used of 3.7 GB available memory,
> with 2.1 GB available for caching and 182 MB free,
> 1.0 GB of the available cache and memory is used,
> no swap space used.
That's not a correct interpretation of the output of "free". What that
output says is that 3.5GB is used, but of that, 363MB + 2.1GB = 2.5GB is
currently being used for buffers and cache. The memory used for buffers
and cache can be made available very quickly, so the second line shows
how much is used (1.0GB) and free (2.7GB) with the buffer and cache
usage ignored. So the real thing to take away from the above is in
the second line: only 1.0GB is used and 2.7GB is free. See
http://unix.stackexchange.com/questions/33541/free-output-format/33549#33549
If I'm right htop and the Gnome system monitor show the amount of 'Mem:'
and 'Swap:' in the 'used' table.
Thanks for your remarks, since yesterday I've read about many things I
didn't know yet.
Jan-Rens.
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