On Sun, 9 Oct 2011 16:45:58 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > hanks for your careful review. > I will send a formal version. > > From 49078e0ebccae371b04930ae76dfd5ba158032ca Mon Sep 17 00:00:00 2001 > From: Minchan Kim <minchan.kim@xxxxxxxxx> > Date: Sun, 9 Oct 2011 16:38:40 +0900 > Subject: [PATCH] vmscan: judge zone's all_unreclaimable carefully > > Shaohua Li reported all_unreclaimable of DMA zone is always set > because the system has a big memory HIGH zone so that lowmem_reserve[HIGH] > could be a big. > > It could be a problem as follows > > Assumption : > 1. The system has a big high memory so that lowmem_reserve[HIGH] of DMA zone would be big. > 2. HIGH/NORMAL zone are full but DMA zone has enough free pages. > > Scenario > 1. A request to allocate a page in HIGH zone. > 2. HIGH/NORMAL zone already consumes lots of pages so that it would be fall-backed to DMA zone. > 3. In DMA zone, allocator got failed, too becuase lowmem_reserve[HIGH] is very big so that it wakes up kswapd > 4. kswapd would call shrink_zone while it see DMA zone since DMA zone's lowmem_reserve[HIGHMEM] > would be big so that it couldn't meet zone_watermark_ok_safe(high_wmark_pages(zone) + balance_gap, > *end_zone*) > 5. DMA zone doesn't meet stop condition(nr_slab != 0, !zone_reclaimable) because the zone has small lru pages > and it doesn't have slab pages so that kswapd would set all_unreclaimable of the zone to *1* easily. > 6. B request to allocate many pages in NORMAL zone but NORMAL zone has no free pages > so that it would be fall-backed to DMA zone. > 7. DMA zone would allocates many pages for NORMAL zone because lowmem_reserve[NORMAL] is small. > These pages are used by application(ie, it menas LRU pages. Yes. Now DMA zone could have many reclaimable pages) > 8. C request to allocate a page in NORMAL zone but he got failed because DMA zone doesn't have enough free pages. > (Most of pages in DMA zone are consumed by B) > 9. Kswapd try to reclaim lru pages in DMA zone but got failed because all_unreclaimable of the zone is 1. Otherwise, > it could reclaim many pages which are used by B. > > Of coures, we can do something in DEF_PRIORITY but it couldn't do enough because it can't raise > synchronus reclaim in direct reclaim path if the zone has many dirty pages > so that the process is killed by OOM. > > The principal problem is caused by step 8. > In step 8, we increased # of lru size very much but still the zone->all_unreclaimable is 1. > If we increase lru size, it is valuable to try reclaiming again. > The rationale is that we reset all_unreclaimable to 0 even if we free just a one page. > > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxx> > Cc: Johannes Weiner <jweiner@xxxxxxxxxx> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Reported-by: Shaohua Li <shaohua.li@xxxxxxxxx> > Reviewed-by: Shaohua Li <shaohua.li@xxxxxxxxx> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> Hmm, catching changes of page usage in a zone ? And this will allow to catch swap_on() and make a zone reclaimable even if no page usage changes. right ? Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>