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

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Message-Id: <20070313.144805.28789513.davem@davemloft.net>
Date:	Tue, 13 Mar 2007 14:48:05 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mpm@...enic.com
Cc:	jeremy@...p.org, nickpiggin@...oo.com.au,
	akpm@...ux-foundation.org, clameter@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [QUICKLIST 0/4] Arch independent quicklists V2

From: Matt Mackall <mpm@...enic.com>
Date: Tue, 13 Mar 2007 16:14:35 -0500

> Well you -could- do this:
> 
> - reuse a long in struct page as a used map that divides the page up
>   into 32 or 64 segments
> - every time you set a PTE, set the corresponding bit in the mask
> - when we zap, only visit the regions set in the mask
> 
> Thus, you avoid visiting most of a PMD page in the sparse case,
> assuming PTEs aren't evenly spread across the PMD.
> 
> This might not even be too horrible as the appropriate struct page
> should be in cache with the appropriate bits of the mm already locked,
> etc.

Yes, I've even had that idea before.

You can even hide it behind pmd_none() et al., the generic VM
doesn't even have to know that the page table macros are doing
this optimization.
-
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