Re: ll_rw_block/submit_bh and request limits

[Marcelo Tosatti]

On Thu, 22 Feb 2001, Andrea Arcangeli wrote:

> On Thu, Feb 22, 2001 at 10:59:20AM -0800, Linus Torvalds wrote:
> > I'd prefer for this check to be a per-queue one.
> 
> I'm running this in my tree since a few weeks, however I never had the courage
> to post it publically because I didn't benchmarked it carefully yet and I
> prefer to finish another thing first. 

You want to throttle IO if the amount of on flight data is higher than
a given percentage of _main memory_. 

As far as I can see, your patch avoids each individual queue from being
bigger than the high watermark (which is a percentage of main
memory). However, you do not avoid multiple queues together from being
bigger than the high watermark.