Messages in this thread | | | Date | Wed, 5 Sep 2007 14:45:46 +0300 | From | Sami Farin <> | Subject | Re: kernel 2.6.22: what IS the VM doing? |
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On Tue, Sep 04, 2007 at 21:37:35 -0400, Rik van Riel wrote: > Sami Farin wrote: >> Using SMP kernel 2.6.22.6pre-CFS-v20.5 on Pentium D (IA-32). >> I think this bug (or whatever you want to call it) got triggered >> when you first allocate several megabytes of memory in a kernel module >> and then free them, and then run e.g. X and when memory gets tight, >> you end up with this situation... >> Top 2 /proc/vmstat Biggest Winners: >> pgrefill_normal:49900/second >> pgrefill_high:20810/second > > That means the pageout code was scanning about 70000 pages > per second on your system during peak stress. You may have > run into a scalability problem in the Linux kernel, where it > wants to clear the referenced bit off all the anonymous pages > before swapping something out.
Thanks for analysis...
Why turning off swap did not make any difference? Why does is not keep e.g. xterm in memory (which I had 700MB free)?
> To make matters worse, that unlucky page gets chosen because > it was the page where kswapd started scanning. It has little > to do with being the least recently used page, because every > anonymous page tends to have its referenced bit set by the time > we start scanning. > > On truly enormous systems, say with 256GB of memory, kswapd > sometimes needs to scan hundreds of thousands or even millions > of pages before finding something to swap out. Not fun. > >> Did I forget to include some info??? >> Oh, and I need to reboot in order to get usable system >> when this bug happens. > > Is the system trying to evict pages like crazy when your > system becomes unusable?
I think so..
> If so, I wonder if kswapd is simply doing the wrong thing > and trying to evict data from all zones, simply because the > highmem zone is low on free pages...
*shrug*
-- "If we put the Pentagon's personnel managers in charge of the Sahara Desert, they would run out of sand in five years." -Sayen Report
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