How to tune vm to be less swap happy?

How to tune vm to be less swap happy?

[Andrea Aime]

Hi everybody,
sorry to bother you with this question, but I feel that current vm defaults 
are not tuned for a workstation use, but for a file server/db server use.
I work on a couple of machines with 128MB of RAM, tipically use KDE 3.0
and Netbeans (a Java IDE). Ok, I use bloated software, I should have more
RAM. Fine. But what I don't understand is why the system keeps swapping
data in and out just because it doesn't want to shrink the cache below 40 MB.
My typical memory occupation is:

             total       used       free     shared    buffers     cached
Mem:        127096     123264       3832          0       1216      48164
-/+ buffers/cache:      73884      53212
Swap:       257000      62316     194684

Now, as you can see I would need 135 MB to keep all my programs in memory,
and if you look at top output:

 PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
 4397 wolf       9   0 79196  71M 30472 S     0,0 57,4   0:00 java
 4398 wolf       8   0 79196  71M 30472 S     0,0 57,4   0:00 java
...

you'll notice that due to the cache behaviour not even netbeans fits enterely 
in memory. I really doubt that I can benefit from a 48MB disk cache since the 
system is swapping in and out every time I open konqueror, kmail and the 
like... is there anything I can do to shrink the cache and to allow a bigger 
part of my working set to fit into memory? Moreover, what vm tuning do you
advice for a typical workstation use with memory hungry applications?
Best regards
Andrea Aime

Re: How to tune vm to be less swap happy?

[Sean Neakums]

commence  Andrea Aime quotation:

> sorry to bother you with this question, but I feel that current vm
> defaults are not tuned for a workstation use, but for a file
> server/db server use.
> [...] is there anything I can do to shrink the cache and to allow a
> bigger part of my working set to fit into memory? Moreover, what vm
> tuning do you advice for a typical workstation use with memory
> hungry applications?

I've found the rmap VM[0] to be a lot less swap-happy than the stock
VM.  For example, I don't come in in the morning to find that the
updatedb run has pushed everything into swap and bloated the inode and
dentry caches to ridiculous sizes.  There is also a patch around for
the stock VM, but I haven't tried it and I don't know what it does.

[0] http://www.surriel.com/patches/  -- I used the March 1 patch on
    2.4.18 and am now running with the April 9 patch.

-- 
 /////////////////  |                  | The spark of a pin
<sneakums@zork.net> |  (require 'gnu)  | dropping, falling feather-like.
 \\\\\\\\\\\\\\\\\  |                  | There is too much noise.

Re: How to tune vm to be less swap happy?

[Andrea Aime]

Sean wrote:
> I've found the rmap VM[0] to be a lot less swap-happy than the stock
> VM.  For example, I don't come in in the morning to find that the
> updatedb run has pushed everything into swap and bloated the inode and
> dentry caches to ridiculous sizes.  There is also a patch around for
> the stock VM, but I haven't tried it and I don't know what it does.

Thank you for your answer, Sean.
I've tried 2.4.19-pre6 (with preempt-patch), 2.4.19pre7ac2 (with rmap),
2.4.19-pre7aa2. The rmap kernel behaved a bit better by avoid swapping-out
to swap-in a second later (compared to aa), but still suffered (IMHO) from an 
oversized cache. The stock kernel was the worst one, of course.
The final cache size doesn't seem to depend much on the kernel, that's because
I asked for VM tune parameters. I also noticed that aa kernel dropped cache 
size down to 24MB, but only after one hour without any activity (had 
lunch...). BTW, please cc me, I'm not on the list, 
Best regards
Andrea Aime