Re: Audio skips when RAM is ~full

[Anthony DiSante]

Willy Tarreau wrote:
> Hello !
>
> On Sat, Nov 01, 2003 at 12:31:15AM -0500, Anthony DiSante wrote:
>
> > The kernel is buffering the contents of each directory (album) that it 
> > reads (and also, mpg321 copies each mp3 file into RAM before playing it?).  
> > I understand that the idea is to stuff as much into RAM as possible to 
> > reduce pagefile usage, and that the kernel will reclaim memory utilized by 
> > buffers if/when it needs to.  But apparently that isn't happening fast 
> > enough to allow a realtime process like music-playing to work skip-free on 
> > this system with this soundcard.  I think that if I could regularly 
> > forcibly dump the buffered stuff out of the RAM (dropping the used-RAM 
> > percentage down to, say, 10%, like at boot time) then this would make the 
> > skipping stop.
>
>
> 1) are you certain that none of your programs (including mpg321) leaks
>    memory ? As I understand it, it's really the cache which fills memory.

No, I'm not certain that mpg321 (or any other app, though there's 
next-to-nothing else running) is leak-free.

> 2) you can try to preload your file into the cache just before playing it :
>    cp $file /dev/null ; mpg321 $file

But wouldn't "cp $file /tmp/ramdisk0; mpg321 /tmp/ramdisk0/$file" accomplish 
the same thing?  (I've done that.)

> > So... do I have a correct understanding of the problem, and a correct 
> > analysis of the kernel/mem issues that are related to it?  Is it possible 
> > to clear some of the RAM; if so, would that help?
>
>
> Unless a leak happens somewhere in the kernel, sound driver, etc..., memory
> consumed by programs is restored when your programs exit. The only part which
> is not restored immediately is the cache.
>
> BTW, there may be one other reason for your problem. Considering that you
> scan your disk to find random albums, I think that the system updates all
> directories access time after 5s, thus preventing your player from reading
> an uncached file fast enough. You might be interested in mounting it with
> the 'noatime,nodiratime' options in /etc/fstab.

Actually, I don't scan the disk to find random albums; I have a text file 
that contains a list of every album's full path, and I pick a random line 
from that file.  So only the selected album's directory gets scanned.  And 
the mp3 partition is mounted read-only (I should have mentioned that 
before), so the atimes shouldn't be getting written as it is.

> You might also want to try 2.4.23pre9 which includes VM changes compared to
> 2.4.22, and seems quite stable to me.

Maybe I will give that a try.

So I'm guessing that there isn't actually a way to manually move buffer-data 
out of RAM?

-Anthony
http://nodivisions.com/
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