Re: [RFC] Remove unswappable anonymous pages off the LRU

[Christoph Lameter <clameter@sgi.com>]

On Fri, 16 Feb 2007, KAMEZAWA Hiroyuki wrote:

> > On 64 bit platforms we can add one unsigned long to get from 56 to 64 
> > bytes.
> > 
> 
> I sometimes dreams 
> ==
> struct page {
> 	...
> 	struct zone	*zone;
> 	...
> };
> #define page_zone(page)		(page)->zone
> ==
> but never tried ;)

Hmmm..... Currently we have

static inline struct zone *page_zone(struct page *page)
{
        return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
}

page_to_nid is extracting a piece of the page flags. Then we need to do a 
lookup and find the zonenum (another extract from page flags).

This is not expensive. Look at __pagevec_lru_add. This boils down to (r9 
= struct page * ):

0xa000000100117ef0 <__pagevec_lru_add+80>:      [MMI]       ld8 r33=[r9];;
0xa000000100117ef1 <__pagevec_lru_add+81>:                  ld8 r8=[r33]
0xa000000100117ef2 <__pagevec_lru_add+82>:                  nop.i 0x0;;
0xa000000100117f00 <__pagevec_lru_add+96>:      [MII]       nop.m 0x0
0xa000000100117f01 <__pagevec_lru_add+97>:                  shr.u r3=r8,54;;
0xa000000100117f02 <__pagevec_lru_add+98>:                  nop.i 0x0
0xa000000100117f10 <__pagevec_lru_add+112>:     [MMI]       shladd r14=r3,3,r15;;
0xa000000100117f11 <__pagevec_lru_add+113>:                 ld8 r34=[r14]
0xa000000100117f12 <__pagevec_lru_add+114>:                 nop.i 0x0;;
0xa000000100117f20 <__pagevec_lru_add+128>:     [MIB]       nop.m 0x0
0xa000000100117f21 <__pagevec_lru_add+129>:                 cmp.eq p6,p7=r2,r34

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