linux-kernel - Re: [Tux3] Tux3 report: Tux3 Git tree available

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Message-Id: <200903122345.13787.nickpiggin@yahoo.com.au>
Date:	Thu, 12 Mar 2009 23:45:13 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Daniel Phillips <phillips@...nq.net>,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Tux3] Tux3 report: Tux3 Git tree available

On Thursday 12 March 2009 23:32:30 Matthew Wilcox wrote:
> On Thu, Mar 12, 2009 at 05:24:33AM -0700, Daniel Phillips wrote:
> > On Thursday 12 March 2009, Nick Piggin wrote:
> > > That's interesting. Do you handle 1K block sizes with 64K page size? :)
> >
> > Not in its current incarnation.  That would require 32 bytes worth of
> > state while the current code just has a 4 byte map (4 bits X 8 blocks).
> > I suppose a reasonable way to extend it would be 4 x 8 byte maps.  Has
> > somebody spotted a 64K page?
>
> I believe SGI ship their ia64 kernels configured this way.  Certainly
> 16k ia64 kernels are common, which would (if I understand your scheme
> correctly) be 8 bytes worth of state in your scheme.

I think some distros will (or do) ship configs with 64K page size for
ia64 and powerpc too. I think I have heard of people using 64K pages
with ARM. There was some (public) talk of x86-64 getting a 16K or 64K
page size too (and even if not HW, some people want to be able to go
bigger SW pagecache size).

I wouldn't expect 64K page and 1K block to be worth optimising for
(although 64K page systems could easily use older or shared 4K block
filesystems). But just keep in mind that a good solution should not
rely on PAGE_CACHE_SIZE for correctness.

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