Messages in this thread | | | Date | Wed, 25 Nov 2009 21:35:09 +0100 | From | Johannes Weiner <> | Subject | Re: [PATCH] vmscan: do not evict inactive pages when skipping an active list scan |
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Hello all,
On Wed, Nov 25, 2009 at 01:37:52PM -0500, Rik van Riel wrote: > In AIM7 runs, recent kernels start swapping out anonymous pages > well before they should. This is due to shrink_list falling > through to shrink_inactive_list if !inactive_anon_is_low(zone, sc), > when all we really wanted to do is pre-age some anonymous pages to > give them extra time to be referenced while on the inactive list.
I do not quite understand what changed 'recently'.
That fall-through logic to keep eating inactives when the ratio is off came in a year ago with the second-chance-for-anon-pages patch..?
> The obvious fix is to make sure that shrink_list does not fall > through to scanning/reclaiming inactive pages when we called it > to scan one of the active lists. > > This change should be safe because the loop in shrink_zone ensures > that we will still shrink the anon and file inactive lists whenever > we should.
It was not so obvious to me ;)
At first, I thought it would make sense to actively rebalance between the lists if the inactive one grows too large (the fall-through case).
But shrink_zone() does not know about this and although we scan inactive pages, we do not account for them and decrease the 'nr[lru]' for active pages instead, effectively shifting the 'active todo' over to the 'inactive todo'. I can imagine this going wrong!
So I agree, we should use the inactive_*_is_low() predicate only passively.
> Reported-by: Larry Woodman <lwoodman@redhat.com> > Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> diff --git a/mm/vmscan.c b/mm/vmscan.c > index 777af57..ec4dfda 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1469,13 +1469,15 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, > { > int file = is_file_lru(lru); > > - if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) { > - shrink_active_list(nr_to_scan, zone, sc, priority, file); > + if (lru == LRU_ACTIVE_FILE) { > + if (inactive_file_is_low(zone, sc)) > + shrink_active_list(nr_to_scan, zone, sc, priority, file); > return 0; > } > > - if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) { > - shrink_active_list(nr_to_scan, zone, sc, priority, file); > + if (lru == LRU_ACTIVE_ANON) { > + if (inactive_file_is_low(zone, sc)) > + shrink_active_list(nr_to_scan, zone, sc, priority, file); > return 0; > } > return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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