Re: vm lock contention reduction

Andrew Morton
2002-07-05T23:48:28Z

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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