[PATCH] Adjust alignment of pagevec structure

[PATCH] Adjust alignment of pagevec structure

We can shrink the pagevec structure to cacheline align it.  It is used all
over VM reclaiming and mpage pagecache read code.

Right now it is 140 bytes on 64-bit and 72 bytes on 32-bit.  Thats just a
little bit more than a power of 2 (which will cacheline align), so shrink
it to be aligned: 64 bytes on 32bit and 124bytes on 64-bit.

It now occupies two cachelines most of the time instead of three.

I changed nr and cold to "unsigned short" because they'll never reach 2 ^ 16.

Did some reaim benchmarking on 4way PIII (32byte cacheline), with 512MB RAM:

#### stock 2.6.9-rc1-mm4 ####

Peak load Test: Maximum Jobs per Minute 4144.44 (average of 3 runs)
Quick Convergence Test: Maximum Jobs per Minute 4007.86 (average of 3 runs)

Peak load Test: Maximum Jobs per Minute 4207.48 (average of 3 runs)
Quick Convergence Test: Maximum Jobs per Minute 3999.28 (average of 3 runs)

#### shrink-pagevec #####

Peak load Test: Maximum Jobs per Minute 4717.88 (average of 3 runs)
Quick Convergence Test: Maximum Jobs per Minute 4360.59 (average of 3 runs)

Peak load Test: Maximum Jobs per Minute 4493.18 (average of 3 runs)
Quick Convergence Test: Maximum Jobs per Minute 4327.77 (average of 3 runs)

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>