Re: [RFC 11/16] Variable Page Cache Size: Fix up reclaim counters

[mel@skynet.ie (Mel Gorman)]

On (22/04/07 23:49), Christoph Lameter didst pronounce:
> Variable Page Cache Size: Fix up reclaim counters
> 
> We can now reclaim larger pages. Adjust the VM counters
> to deal with it.
> 
> Note that this does currently not make things work.
> For some reason we keep loosing pages off the active lists
> and reclaim stalls at some point attempting to remove
> active pages from an empty active list.
> It seems that the removal from the active lists happens
> outside of reclaim ?!?
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> ---
>  mm/vmscan.c |   15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6.21-rc7/mm/vmscan.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/mm/vmscan.c	2007-04-22 06:50:03.000000000 -0700
> +++ linux-2.6.21-rc7/mm/vmscan.c	2007-04-22 17:19:35.000000000 -0700
> @@ -471,14 +471,14 @@ static unsigned long shrink_page_list(st
>  
>  		VM_BUG_ON(PageActive(page));
>  
> -		sc->nr_scanned++;
> +		sc->nr_scanned += base_pages(page);
>  
>  		if (!sc->may_swap && page_mapped(page))
>  			goto keep_locked;
>  
>  		/* Double the slab pressure for mapped and swapcache pages */
>  		if (page_mapped(page) || PageSwapCache(page))
> -			sc->nr_scanned++;
> +			sc->nr_scanned += base_pages(page);
>  
>  		if (PageWriteback(page))
>  			goto keep_locked;
> @@ -581,7 +581,7 @@ static unsigned long shrink_page_list(st
>  
>  free_it:
>  		unlock_page(page);
> -		nr_reclaimed++;
> +		nr_reclaimed += base_pages(page);
>  		if (!pagevec_add(&freed_pvec, page))
>  			__pagevec_release_nonlru(&freed_pvec);
>  		continue;
> @@ -627,7 +627,7 @@ static unsigned long isolate_lru_pages(u
>  	struct page *page;
>  	unsigned long scan;
>  
> -	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
> +	for (scan = 0; scan < nr_to_scan && !list_empty(src); ) {
>  		struct list_head *target;
>  		page = lru_to_page(src);
>  		prefetchw_prev_lru_page(page, src, flags);
> @@ -644,10 +644,11 @@ static unsigned long isolate_lru_pages(u
>  			 */
>  			ClearPageLRU(page);
>  			target = dst;
> -			nr_taken++;
> +			nr_taken += base_pages(page);
>  		} /* else it is being freed elsewhere */
>  
>  		list_add(&page->lru, target);
> +		scan += base_pages(page);
>  	}

Be careful here when lumpy reclaim is also involved. By moving scan++
out of the loop, the scan counter increment may be missed because a
continue is involved. Just watch out for it.

I am of two minds on whether we should be counting base pages or not but
it's probably best from an IO perspective....

>  
>  	*scanned = scan;
> @@ -856,7 +857,7 @@ force_reclaim_mapped:
>  		ClearPageActive(page);
>  
>  		list_move(&page->lru, &zone->inactive_list);
> -		pgmoved++;
> +		pgmoved += base_pages(page);
>  		if (!pagevec_add(&pvec, page)) {
>  			__mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
>  			spin_unlock_irq(&zone->lru_lock);
> @@ -884,7 +885,7 @@ force_reclaim_mapped:
>  		SetPageLRU(page);
>  		VM_BUG_ON(!PageActive(page));
>  		list_move(&page->lru, &zone->active_list);
> -		pgmoved++;
> +		pgmoved += base_pages(page);
>  		if (!pagevec_add(&pvec, page)) {
>  			__mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
>  			pgmoved = 0;

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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