Messages in this thread | | | Date | Fri, 6 Jul 2007 04:03:41 -0700 (PDT) | From | Martin Knoblauch <> | Subject | Re: Understanding I/O behaviour |
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Martin Knoblauch wrote: >--- Robert Hancock <hancockr@xxxxxxx> wrote: > >> >> Try playing with reducing /proc/sys/vm/dirty_ratio and see how that >> helps. This workload will fill up memory with dirty data very >> quickly, >> and it seems like system responsiveness often goes down the toilet >> when >> this happens and the system is going crazy trying to write it all >> out. >> > >Definitely the "going crazy" part is the worst problem I see with 2.6 >based kernels (late 2.4 was really better in this corner case). > >I am just now playing with dirty_ratio. Anybody knows what the lower >limit is? "0" seems acceptabel, but does it actually imply "write out >immediatelly"? > >Another problem, the VM parameters are not really well documented in >their behaviour and interdependence.
Lowering dirty_ration just leads to more imbalanced write-speed for the three dd's. Even when lowering the number to 0, the hich load stays.
Now, on another experiment I mounted the FS with "sync". And now the load stays below/around 3. No more "pdflush" daemons going wild. And the responsiveness is good, with no drops.
My question is now: is there a parameter that one can use to force immediate writeout for every process. This may hurt overall performance of the system, but might really help my situation. Setting dirty_ratio to 0 does not seem to do it.
Cheers Martin
------------------------------------------------------ Martin Knoblauch email: k n o b i AT knobisoft DOT de www: http://www.knobisoft.de - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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