Comment 491 for bug 620074

(In reply to comment #477)
> According to http://www.kernel.org/doc/Documentation/sysctl/vm.txt
>
> "Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
> value lower than this limit will be ignored and the old configuration will be
> retained."
>
> Better make that 8192
>
> Also you could try lowering /proc/sys/vm/dirty_ratio

Setting dirty_bytes to 8192 solves the slowdown of me. Of cause it ends up with a troughput from "stress -d 1" which is considerably lower than when dirty_bytes was set to 0 (ie.

<quote-from-doc>
If dirty_bytes is written, dirty_ratio becomes a function of its value
(dirty_bytes / the amount of dirtyable system memory).
</quote-from-doc>

Now, dirty_ratio is 60 by default, so 60% of my system memory can be used for dirty pages. On my system that is 1.2GB. So if I do not have 1.2GB free and I am doing some high troughput write to disk my system will hang. I think it is a bit overkill especially seen in the perspective that a standard harddisk can write no more that 100MB/sec.

The kernel should be reosonable enough to behave and not just hog the majority of system memory during high throughput operations. Just think of system with 8GB of memory and the 6Gb is used by running application. Runnning "stress -d 1" on such a setup would kill it. The writing application would be allowed to use 60% of the 8GB for dirty pages. It seems massive, so please correctly me if I'm wrong since I have not done a test on such a system.