From: Nick Piggin <[email protected]>
Date: Fri, 18 May 2007 07:12:38 +0200
> The page->virtual thing is just a bonus (although have you seen what
> sort of hoops SPARSEMEM has to go through to find page_address?! It
> will definitely be a win on those architectures).
If you set the bit ranges in asm/sparsemem.h properly, as I
have currently on sparc64, it isn't bad at all. It's a
single extra dereference from a table that sits in the main
kernel image and thus is in a locked TLB entry.
SPARSEMEM_EXTREME is pretty much unnecessary and with the
virtual mem-map stuff the sparsemem overhead goes away entirely
and we're back to "page - mem_map" type simple calculations
obviating any dereferencing advantage from page->virtual.
> 0.2% of memory, or 2MB per GB. But considering we already use 14MB per
> GB for the page structures, it isn't like I'm introducing an order of
> magnitude problem.
All these little things add up, let's not suck like some other
OSs by having that kind of mentality.
Show me instead a change that makes page struct 8 bytes smaller
:-))))
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