Messages in this thread Patch in this message | | | Date | Wed, 6 Feb 2008 19:35:12 -0500 | From | Rik van Riel <> | Subject | Re: [patch 05/19] split LRU lists into anon & file sets |
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On Wed, 30 Jan 2008 17:57:54 +0900 KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> I found number of scan pages calculation bug.
My latest version of get_scan_ratio() works differently, with the percentages always adding up to 100. However, your patch gave me the inspiration to (hopefully) find the bug in my version of the code.
> 1. wrong calculation order
I do not believe my new code has this problem. Of course, this is purely due to luck :)
> 2. wrong fraction omission > > nr[l] = zone->nr_scan[l] * percent[file] / 100; > > when percent is very small, > nr[l] become 0.
This is probably where the problem is. Kind of.
I believe that the problem is that we scale nr[l] by the percentage, instead of scaling the amount we add to zone->nr_scan[l] by the percentage!
> @@ -1409,7 +1410,11 @@ static unsigned long shrink_zone(int pri > */ > zone->nr_scan[l] += (zone_page_state(zone, > NR_INACTIVE_ANON + l) >> priority) + 1; > - nr[l] = zone->nr_scan[l] * percent[file] / 100; > + nr[l] = (zone->nr_scan[l] * percent[file] / 100) + 1; > + nr_max_scan = zone_page_state(zone, NR_INACTIVE_ANON+l); > + if (nr[l] > nr_max_scan) > + nr[l] = nr_max_scan; > + > if (nr[l] >= sc->swap_cluster_max) > zone->nr_scan[l] = 0; > else
With the fix below (against my latest tree), we always add at least one to zone->nr_scan[l] and always make that increment count later on!
I am still recovering from my trip home (thanks to the airline companies I spent 25 hours travelling, from door to door), so I may not get around to actually testing this today:
Index: linux-2.6.24-rc6-mm1/mm/vmscan.c =================================================================== --- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c 2008-02-06 19:23:16.000000000 -0500 +++ linux-2.6.24-rc6-mm1/mm/vmscan.c 2008-02-06 19:22:55.000000000 -0500 @@ -1275,13 +1275,17 @@ static unsigned long shrink_zone(int pri for_each_lru(l) { if (scan_global_lru(sc)) { int file = is_file_lru(l); + int scan; /* * Add one to nr_to_scan just to make sure that the - * kernel will slowly sift through the active list. + * kernel will slowly sift through each list. */ - zone->nr_scan[l] += (zone_page_state(zone, - NR_INACTIVE_ANON + l) >> priority) + 1; - nr[l] = zone->nr_scan[l] * percent[file] / 100; + scan = zone_page_state(zone, NR_INACTIVE_ANON + l); + scan >>= priority; + scan = (scan * percent[file]) / 100; + + zone->nr_scan[l] += scan + 1; + nr[l] = zone->nr_scan[l]; if (nr[l] >= sc->swap_cluster_max) zone->nr_scan[l] = 0; else
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