linux-kernel - Re: [PATCH 1/1] mm: add dirty

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Message-Id: <20071126215315.3422eaa2.akpm@linux-foundation.org>
Date:	Mon, 26 Nov 2007 21:53:15 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Bron Gondwana" <brong@...tmail.fm>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Christian Kujau" <lists@...dbynature.de>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Rob Mueller" <robm@...tmail.fm>
Subject: Re: [PATCH 1/1] mm: add dirty_highmem option

On Tue, 27 Nov 2007 16:24:24 +1100 "Bron Gondwana" <brong@...tmail.fm> wrote:

> On Mon, 26 Nov 2007 20:54:28 -0800, "Andrew Morton" <akpm@...ux-foundation.org> said:
> > On Thu, 22 Nov 2007 14:42:04 +1100 Bron Gondwana <brong@...tmail.fm>
> > wrote:
> > 
> > >  /*
> > > + * free highmem will not be subtracted from the total free memory
> > > + * for calculating free ratios if vm_dirty_highmem is true
> > > + */
> > > +int vm_dirty_highmem;
> > 
> > One would expect that setting dirty_highmem to true would cause highmem
> > to
> > be accounted in dirty-memory calculations.  However with this change
> > reality is in fact the inverse of that.
> > 
> > So how about this?
> 
> Actually, I'm confused now.  Maybe I chose a bad name to begin with.
> Does it mean "I am allowed to dirty high memory" or "my high memory
> will be dirty if this is on"?

But we're always allowed to dirty highmem - there'd be no point in having
it otherwise.  Hence the term dirty_highmem is confusing.

umm, really you want
/proc/sys/vm/dont-account-highmem-in-dirty-memory-calculations, only
shorter.

Do you agree?

If so, then it's still not a very pleasing interface - setting something to
"true" to disable a particular piece of kernel behaviour implies a single
negation which we don't really need.

It would be simpler to have
/proc/sys/vm/do-account-highmem-in-dirty-memory-calculations,
defaulting to "true" - this has no negations.

So... how about /proc/sys/vm/, umm.

<looks at inbox, brain explodes>

OK, I give up.  Please see if you can think of something less confusing
which involves no negations?

Thanks.
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