Date: Fri, 18 May 2007 11:14:26 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
To: Nick Piggin <npiggin@suse.de>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Memory Management List <linux-mm@kvack.org>,
       linux-arch@vger.kernel.org
Subject: Re: [rfc] increase struct page size?!
In-Reply-To: <20070518040854.GA15654@wotan.suse.de>
Message-ID: <Pine.LNX.4.64.0705181112250.11881@schroedinger.engr.sgi.com>
References: <20070518040854.GA15654@wotan.suse.de>
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On Fri, 18 May 2007, Nick Piggin wrote:

> However we don't have to let those 8 bytes go to waste: we can use them
> to store the virtual address of the page, which kind of makes sense for
> 64-bit, because they can likely to use complicated memory models.

That is not a valid consideration anymore. There is virtual memmap update 
pending with the sparsemem folks that will simplify things.

> Many batch operations on struct page are completely random, and as such, I
> think it is better if each struct page fits completely into a single
> cacheline even if it means being slightly larger.

Right. That would simplify the calculations.
 
> Don't let this space go to waste though, we can use page->virtual in order
> to optimise page_address operations.

page->virtual is a benefit if the page is cache hot. Otherwise it may 
cause a useless lookup.

I wonder if there are other uses for the free space?

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