Subject: Re: Throttling IO Requests in NetBSD via Congestion Control
To: Sumantra Kundu <>
From: David Laight <>
List: tech-kern
Date: 08/28/2006 21:00:49
On Mon, Aug 28, 2006 at 02:26:35PM -0500, Sumantra Kundu wrote:
> However, if there appears a writer(s) operating on a huge file size (>1mb),
> then all the free pages in the UVM are consumed by the **writer process**
> and the reader is starved due to non-availability of pages. Actually
> even though the CCA works, but its benefits are not easily observable.

My 'gut feel' is that NetBSD is rather unwilling to write out dirty
pages from an open file.  So everyone else ends up fighting over the
few remaining pages when a process is writing to a large file.
However I've not done anything that verify this.

The LRU page allocation code also means that if a process cycles through
'n+1' pages when only 'n' are available, then every access to a new page
results in a fault.


David Laight: