Re: [00/17] Large Blocksize Support V3

From: Nick Piggin
Date: Fri Apr 27 2007 - 08:26:22 EST

Christoph Lameter wrote:
On Fri, 27 Apr 2007, Nick Piggin wrote:

For the TLB issue, higher order pagecache doesn't help. If distros
ship with a 4K page size on powerpc, and use some larger pages in
the pagecache, some people are still going to get angry because
they wanted to use 64K pages... But I agree 64K pages is too big
for most things anyway, and 16 would be better as a default (which
hopefully x86-64 will get one day).

Powerpc supports multiple pagesizes. Maybe we could make mmap use those page sizes some day if we had a variable order page cache. Your stands on the issue means that powerpc will be forever crippled and not be able to use its full potential.

Linus's favourite jokes about powerpc mmu being crippled forever, aside ;)

This seems like just speculation. I would not be against something which,
without, would "cripple" some relevant hardware, but you are just handwaving
at this point. And you are still ignoring the alternatives.

Anyway, for io performance, there are alternatives, dispite what
some people seem to be saying. We can submit larger sglists to the
device for larger ios, which Jens is looking at (which could help
all types of workloads, not just those with sequential large file

Right this could help but it is not addressing the basic requirement for
devices that need large contiguuos chunks of memory for I/O.

Did you read the last paragraph? Or anything Andrew's been writing?

"After that, I'd find it amusing if HBAs worth thousands of $ have
trouble looking up sglists at the relatively glacial pace that IO
requires, and/or can't spare a few more K for reasonable sglist
sizes, but if that is really the case, then we could use iommus
and/or just attempt to put physically contiguous pages in pagecache,
rather than require it."

SUSE Labs, Novell Inc.
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