Hi Minchan and KOSAKI On Fri, Jun 15, 2012 at 3:27 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote: > On 06/15/2012 01:10 AM, KOSAKI Motohiro wrote: > >> On Thu, Jun 14, 2012 at 10:57 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote: >>> Hi KOSAKI, >>> >>> Sorry for late response. >>> Let me ask a question about description. >>> >>> On Thu, Jun 14, 2012 at 04:13:12AM -0400, kosaki.motohiro@xxxxxxxxx wrote: >>>> From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> >>>> >>>> Currently, do_try_to_free_pages() can enter livelock. Because of, >>>> now vmscan has two conflicted policies. >>>> >>>> 1) kswapd sleep when it couldn't reclaim any page when reaching >>>> priority 0. This is because to avoid kswapd() infinite >>>> loop. That said, kswapd assume direct reclaim makes enough >>>> free pages to use either regular page reclaim or oom-killer. >>>> This logic makes kswapd -> direct-reclaim dependency. >>>> 2) direct reclaim continue to reclaim without oom-killer until >>>> kswapd turn on zone->all_unreclaimble. This is because >>>> to avoid too early oom-kill. >>>> This logic makes direct-reclaim -> kswapd dependency. >>>> >>>> In worst case, direct-reclaim may continue to page reclaim forever >>>> when kswapd sleeps forever. >>> >>> I have tried imagined scenario you mentioned above with code level but >>> unfortunately I got failed. >>> If kswapd can't meet high watermark on order-0, it doesn't sleep if I don't miss something. >> >> pgdat_balanced() doesn't recognized zone. Therefore kswapd may sleep >> if node has multiple zones. Hm ok, I realized my descriptions was >> slightly misleading. priority 0 is not needed. bakance_pddat() calls >> pgdat_balanced() >> every priority. Most easy case is, movable zone has a lot of free pages and >> normal zone has no reclaimable page. >> >> btw, current pgdat_balanced() logic seems not correct. kswapd should >> sleep only if every zones have much free pages than high water mark >> _and_ 25% of present pages in node are free. >> > > > Sorry. I can't understand your point. > Current kswapd doesn't sleep if relevant zones don't have free pages above high watermark. > It seems I am missing your point. > Please anybody correct me. > Who left comment on unreclaimable there, and why? /* * balance_pgdat() skips over all_unreclaimable after * DEF_PRIORITY. Effectively, it considers them balanced so * they must be considered balanced here as well if kswapd * is to sleep */ BTW, are you still using prefetch_prev_lru_page? Good Weekend Hillf -- 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/ . Don't email: <a href