Re: vm lock contention reduction

[Andrew Morton <akpm@zip.com.au>]

William Lee Irwin III wrote:
> 
> On Thu, Jul 04, 2002 at 07:18:34PM -0700, Andrew Morton wrote:
> > Of course, that change means that we wouldn't be able to throttle
> > page allocators against IO any more, and we'd have to do something
> > smarter.  What a shame ;)
> 
> This is actually necessary IMHO. Some testing I've been able to do seems
> to reveal the current throttling mechanism as inadequate.
> 

I don't think so.  If you're referring to the situation where your
4G machine had 3.5G dirty pages without triggering writeback.

That's not a generic problem.  It's something specific to your
setup.  You're going to have to repeat it and stick some printk's
into balance_dirty_pages().  No other way of finding it.

Possibly it's an arith overflow in there, but I more suspect that
your nr_pagecache_pages() function is returning an incorrect value.

This happened to David M-T just this week in the 2.4 kernel - the
nr_buffermem_pages() function was returning a bad value due to an
unaccounted-for hole in the memory map and the observed effect
was just the same.

So.  Please debug it.

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