linux-kernel - Re: [QUICKLIST 0/4] Arch independent quicklists V2

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Message-ID: <Pine.LNX.4.64.0703151324150.27311@schroedinger.engr.sgi.com>
Date:	Thu, 15 Mar 2007 13:28:36 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-mm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [QUICKLIST 0/4] Arch independent quicklists V2

On Tue, 13 Mar 2007, Andrew Morton wrote:

> > 1. We need to support other states of pages other than zeroed.
> 
> What does this mean?

pgd are not completely zeroed. They contain mappings that are always 
present. Thus the state is not a zeroed state.

> > 2. Prezeroing does not make much sense if a large portion of the
> >    page is being used. Performance is better if the whole page 
> >    is zeroed directly before use.Prezeroing only makes sense for sparse
> >    allocations like the page table pages.
> 
> This is not related to the above discussion.

Really? I definitely see the word prezeroing in the discussion.

> > I already tried that 3 years ago and there was *no* benefit for usual
> > users of the a page allocator. The advantage exists only if a small
> > portion of the page is used. F.e. For one cacheline there was a 4x 
> > improvement. See lkml archives for prezeroing.
> 
> Unsurprised.  Were non-temporal stores tried?

Yes with no material change. The work lead to making ia64 use non 
temporal stores for spin unlock but it was not useful for prezeroing.

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