Re: [RFC][PATCH 0/4] ZERO PAGE again v2

[Nick Piggin <npiggin@suse.de>]

On Mon, Jul 13, 2009 at 08:46:41AM +0200, Nick Piggin wrote:
> On Fri, Jul 10, 2009 at 12:18:07PM +0100, Hugh Dickins wrote:
> > On Wed, 8 Jul 2009, Andrea Arcangeli wrote:
> > > On Tue, Jul 07, 2009 at 06:06:29PM +0900, KAMEZAWA Hiroyuki wrote:
> > > harmful as there's a double page fault generated instead of a single
> > > one, kksmd has a cost but zeropage isn't free either in term of page
> > > faults too)
> > 
> > Much as I like KSM, I have to agree with Avi, that if people are
> > wanting the ZERO_PAGE back in compute-intensive loads, then relying
> 
> I can't imagine ZERO_PAGE would be too widely used in compute-intensive
> loads. At least, not serious stuff. Nobody wants to spend 4K of cache
> and one TLB entry for one or two non-zero floating point numbers in a
> big sparse matrix. Not to mention the cache and memory overhead of just
> scanning through lots of zeros.

Heh, oops: before anyone thinks it will be fun to make some
personal insults, there won't be much memory overhead from
zero page of course! Cache and *TLB* overhead is going to be
involved.

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