Mailinglist Archive: packet-writing (32 mails)

[Jens Axboe <axboe@xxxxxxx>]

On Thu, May 29 2003, Peter Osterlund wrote:
> On Tue, 27 May 2003, Sergiy Kudryk wrote:
> 
> > I have a problem with temporary system locking when performing
> > packet writing using pktcdvd with filled buffer ..
> > 
> > Utility top shows low pktcdvd CPU/memory utilize ..
> > 
> > What's up ?
> 
> This old explanation is still valid, I think:
> 
> 	http://lists.suse.com/archive/packet-writing/2002-Jul/0046.html
> 
> 	"The ext2 filesystem doesn't have this property. It adds files at
> 	full speed without reading anything from the disk, until all your
> 	memory fills up with dirty data. When this happens the system
> 	becomes very unresponsive (as in mouse pointer in X freezes for
> 	minutes), because every process that tries to allocate memory is
> 	put to sleep.
> 
> 	So the performance problem in the udf filesystem is hiding another
> 	problem in the virtual memory subsystem. The VM should only allow
> 	a fraction of the total RAM to be used for dirty data belonging to
> 	a slow block device."
> 
> I'm not sure if 2.5 handles this better than 2.4.

2.5 handles it much better. There's more to the problem than what is
described above. Basically in 2.4 we have a single dirty buffer list, so
if we get stuck writing out 150MB to a cd-rw device, it's impossible to
free other memory. Only much much later will we make some progress.

2.5 has several flusher threads, and a per-mapping dirty page list. Even
a modest machine can keep many spindles going full throttle with ease.

-- 
Jens Axboe