linux-kernel - Re: [rfc] increase struct page size?!

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Message-ID: <20070518073223.GA23998@wotan.suse.de>
Date:	Fri, 18 May 2007 09:32:23 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc] increase struct page size?!

On Fri, May 18, 2007 at 12:19:05AM -0700, Andrew Morton wrote:
> On Fri, 18 May 2007 06:08:54 +0200 Nick Piggin <npiggin@...e.de> wrote:
> 
> > Many batch operations on struct page are completely random,
> 
> But they shouldn't be: we should aim to place physically contiguous pages
> into logically contiguous pagecache slots, for all the reasons we
> discussed.

For big IO batch operations, pagecache would be more likely to be
physically contiguous, as would LRU, I suppose.

I'm more thinking of operations where things get reclaimed over time,
touched or dirtied in slightly different orderings, interleaved with
other allocations, etc.


> If/when that happens, there will be a *lot* of locality of reference
> against the pageframes in a lot of important codepaths.

And when it doesn't happen, we eat 75% more cache misses. And for that
matter we eat 75% more cache misses for non-batch operations like
allocating or freeing a page by slab, for example.

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