Re: [rfc] increase struct page size?!

[David Miller]

From: Nick Piggin <npiggin@xxxxxxx>
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
:-))))
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/