The using of memory buffer/cache and free

The using of memory buffer/cache and free

[RichardR]

Hi all,
I just want to wipe out some doubts in my knowledges about how
processes and kernel use memory buffer/cache and memory free.
My doubt is, when I run the first time my machine and when I run
"free"... it shows me corrret numbers. no memory leaks on view...

Now when I try to run some process, like a  simple rsync transfer
which takes some time to finish...I just can see that my "free" goes
down, which can be explained with the rsync activities...
after some minutes...the rsync ended and what I can still see is this:

root@4[root]# free
             total       used       free     shared    buffers     cached
Mem:       2075428    2051948      23480          0      10872    1965908
-/+ buffers/cache:      75168    2000260
Swap:            0          0          0
--
Memory free is not flushed out even after an "update" or "sync" and
cached is highly stored.

Now when I want to know the total load of memory used by running
processes, I can find only 151320 bytes used! and my total memory is
2Gb, the rest is on cached...

root@4[root]# ps auwwx | sort -n +4 | awk 'BEGIN{a=0}($5 > 0) { a+=$5;
print $5,$11 }END{print a}' | grep -v sort | tail +2
76 init
1564 grep
1628 /usr/sbin/automount
1752 tail
1920 awk
2512 ps
2572 /bin/sh
2572 /bin/sh
3108 /usr/sbin/sshd
3432 /bin/bash
3432 /bin/bash
3432 /bin/bash
3432 /bin/bash
3440 -bash
6076 sshd:
6700 icewm
6700 -bash
6700 -bash
6736 -bash
9944 xterm
9944 xterm
10252 xterm
26248 XFree86
151320

my question is: is it normal that such a process can demande such
memory free and then cached by the kernel without being flushed after
used?
Thanks guys in advance for your lights...
Cheers
-- 
Richard R.
IT Soft/System Engineer
CNRS/IN2P3/LPNHE 
Jussieu - Paris VI
--
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>

Re: The using of memory buffer/cache and free

[Christian Smith]

On Tue, 5 Apr 2005, RichardR wrote:

>Hi all,
>I just want to wipe out some doubts in my knowledges about how
>processes and kernel use memory buffer/cache and memory free.
>My doubt is, when I run the first time my machine and when I run
>"free"... it shows me corrret numbers. no memory leaks on view...
>
>Now when I try to run some process, like a  simple rsync transfer
>which takes some time to finish...I just can see that my "free" goes
>down, which can be explained with the rsync activities...
>after some minutes...the rsync ended and what I can still see is this:
>
>root@4[root]# free
>             total       used       free     shared    buffers     cached
>Mem:       2075428    2051948      23480          0      10872    1965908
>-/+ buffers/cache:      75168    2000260
>Swap:            0          0          0
>--
>Memory free is not flushed out even after an "update" or "sync" and
>cached is highly stored.
>
>Now when I want to know the total load of memory used by running
>processes, I can find only 151320 bytes used! and my total memory is
>2Gb, the rest is on cached...

That's 151320K, BTW.


>
> [snip ps output]
>
>my question is: is it normal that such a process can demande such
>memory free and then cached by the kernel without being flushed after
>used?


The data in the cache will be flushed (if it is dirty) back to disc as and
when required, but will stay in memory in case it is used again, that is
the nature of a cache.

If memory pressure dictates memory reuse, the cache size will be reduced
to make memory available. But while there is no memory pressure, it might
as well be left in memory.


Christian

-- 
    /"\
    \ /    ASCII RIBBON CAMPAIGN - AGAINST HTML MAIL
     X                           - AGAINST MS ATTACHMENTS
    / \
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>