Re: Large slab cache in 2.6.1

[Nick Piggin <piggin@cyberone.com.au>]

Chris Wedgwood wrote:

>On Sun, Feb 22, 2004 at 04:37:46PM +1100, Nick Piggin wrote:
>
>
>>Can you upgrade to 2.6.3-mm2? It would be ideal if you could test
>>this patch against that kernel due to the other VM changes.
>>
>
>Sure.
>
>
>>Chris, could you test this too please? Thanks.
>>
>
>I tested this change to a stock 2.6.3 kernel and saw a marginally
>better situation... 650MB in slab instead of 850MB:
>

In your case, this is probably ideal if the system is
not doing much. You now have a reasonable amount of low
memory available.


>
>===== page_alloc.c 1.186 vs edited =====
>--- 1.186/mm/page_alloc.c	Wed Feb 18 19:43:04 2004
>+++ edited/page_alloc.c	Sat Feb 21 21:05:32 2004
>@@ -764,13 +764,18 @@
> 
> EXPORT_SYMBOL(nr_free_pages);
> 
>+/*
>+ * return the number of non-highmem pages (we should probably rename
>+ * this function? --cw)
>+ */
> unsigned int nr_used_zone_pages(void)
> {
> 	unsigned int pages = 0;
> 	struct zone *zone;
> 
> 	for_each_zone(zone)
>-		pages += zone->nr_active + zone->nr_inactive;
>+		if (!is_highmem(zone))
>+		    pages += zone->nr_active + zone->nr_inactive;
> 
> 	return pages;
> }
>
>
>I'll test -mm2 with your patch shortly.
>
>

My patch will be functionally the same as yours so you'll be
mainly testing the other VM changes (which isn't a bad thing).
Thanks.

>
>>@@ -145,7 +145,7 @@ static int shrink_slab(unsigned long sca
>> 	if (down_trylock(&shrinker_sem))
>> 		return 0;
>> 
>>-	pages = nr_used_zone_pages();
>>+	pages = nr_lowmem_lru_pages();
>>
>
>Cool. I think renaming this i a good idea.
>
>

Yep.

>>-unsigned int nr_used_zone_pages(void)
>>+unsigned int nr_lowmem_lru_pages(void)
>> {
>>+	pg_data_t *pgdat;
>> 	unsigned int pages = 0;
>>-	struct zone *zone;
>> 
>>-	for_each_zone(zone)
>>-		pages += zone->nr_active + zone->nr_inactive;
>>+	for_each_pgdat(pgdat) {
>>+		int i;
>>+		for (i = 0; i < ZONE_HIGHMEM; i++) {
>>+			struct zone *zone = pgdat->node_zones + i;
>>+			pages += zone->nr_active + zone->nr_inactive;
>>+		}
>>+	}
>>
>
>Why not just check is_highmem(zone) here?
>
>

Why indeed? Easier to read vs a tiny bit faster. It isn't
really a fast path, so your version is probably better.

>>-extern unsigned int nr_used_zone_pages(void);
>>+extern unsigned int nr_lowmem_lru_pages(void);
>>
>
>Since shrink_slab() is the only consumer of this why not move the
>function to vmscan.c just above shrink_slab()?
>
>

Might as well I suppose. I'll incorporate your suggestions if
it tests well and I end up sending it off to Andrew.