linux-kernel - Re: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support

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Message-Id: <20070614150417.c73fb6b9.akpm@linux-foundation.org>
Date:	Thu, 14 Jun 2007 15:04:17 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [patch 00/14] Page cache cleanup in anticipation of Large
 Blocksize support

> On Thu, 14 Jun 2007 14:37:33 -0700 (PDT) Christoph Lameter <clameter@....com> wrote:
> On Thu, 14 Jun 2007, Andrew Morton wrote:
> 
> > We want the 100% case.
> 
> Yes that is what we intend to do. Universal support for larger blocksize. 
> I.e. your desktop filesystem will use 64k page size and server platforms 
> likely much larger.

With 64k pagesize the amount of memory required to hold a kernel tree (say)
will go from 270MB to 1400MB.   This is not an optimisation.

Several 64k pagesize people have already spent time looking at various
tail-packing schemes to get around this serious problem.  And that's on
_server_ class machines.  Large ones.  I don't think
laptop/desktop/samll-server machines would want to go anywhere near this.

> fsck times etc etc are becoming an issue for desktop 
> systems

I don't see what fsck has to do with it.

fsck is single-threaded (hence no locking issues) and operates against the
blockdev pagecache and does a _lot_ of small reads (indirect blocks,
especially).  If the memory consumption for each 4k read jumps to 64k, fsck
is likely to slow down due to performing a lot more additional IO and due
to entering page reclaim much earlier.

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