Re: BUG: Slowdown on 3000 socket-machines tracked down

[Nick Piggin <nickpiggin@yahoo.com.au>]

Christian Schmid wrote:

> Today I tested with 5000 sockets. The problem is the same like above but 
> the more sockets there come, it just doesnt claim more bandwidth as it 
> SHOULD of course do. It seems it doesn't slow down but it just doesnt 
> scale anymore. The badwidth doesnt go over 80 MB/Sec, no matter what I 
> do. Then I did the following: I raised lower_zone_protection to 1024 
> (above I did 1024000 which is bullshit but it doesnt matter as it seems 
> to just protect the whole low-mem which is what I want) and it was at 80 
> MB. then I lowered to 0 again and suddenly it peaked up to full 
> bandwidth (100 MB) for about 5 seconds until the whole protected area 
> was in use. Then it slowed down drastically again.

This confirms my suspicion that lowmem / highmem scanning is not
properly balanced. When you raise lower_zone_protection a great
deal, lowmem is no longer used for pagecache, and your problem
goes away.

I gave you a patch to try for this - unfortunately I can't make
much more progress than that if I don't have a test case and you
can't test patches :\

Nick