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SubjectRe: [PATCH -mm 02/25] Use an indexed array for LRU variables
On Fri, 6 Jun 2008 18:04:26 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> I would have spat the dummy at pointless churn and code uglification
> but I see that we end up with five LRU lsits so ho hum.

> > /* Fields commonly accessed by the page reclaim scanner */
> > spinlock_t lru_lock;
> > - struct list_head active_list;
> > - struct list_head inactive_list;
> > - unsigned long nr_scan_active;
> > - unsigned long nr_scan_inactive;
> > + struct list_head list[NR_LRU_LISTS];
> > + unsigned long nr_scan[NR_LRU_LISTS];
>
> It'd be a little cache-friendlier to lay this out as
>
> struct {
> struct list_head list;
> unsigned long nr_scan;
> } lru_stuff[NR_LRU_LISTS];

OK, done. As zone.lru though for brevity.

> > +++ linux-2.6.26-rc2-mm1/include/linux/mm_inline.h 2008-05-23 14:21:33.000000000 -0400
> > @@ -1,40 +1,51 @@
> > static inline void
> > +add_page_to_lru_list(struct zone *zone, struct page *page, enum lru_list l)
> > +{
> > + list_add(&page->lru, &zone->list[l]);
> > + __inc_zone_state(zone, NR_INACTIVE + l);
>
> ^ that's a bug, isn't it?
>
> oh, no it isn't.
>
> Can we rename NR_INACTIVE? Maybe VMSCAN_BASE or something?

I turned it into NR_LRU_BASE, since everything in zone_stat_item
starts with NR_

enum zone_stat_item {
/* First 128 byte cacheline (assuming 64 bit words) */
NR_FREE_PAGES,
NR_LRU_BASE,
NR_INACTIVE = NR_LRU_BASE, /* must match order of LRU_[IN]ACTIVE */
NR_ACTIVE, /* " " " " " */

> > - if (PageActive(page))
> > - add_page_to_active_list(zone, page);
> > - else
> > - add_page_to_inactive_list(zone, page);
> > + add_page_to_lru_list(zone, page, PageActive(page));
>
> urgh. the third arg to add_page_to_lru_list() is an `enum lru_list'
> and here we are secretly coercing PageActive()'s boolean return into a
> just-happens-to-be-right `enum lru_list'.
>
> That's pretty nasty?

I've pulled page_lru() back from patch 03/25 into 02/25 and
will use that.

--
All rights reversed.


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