Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755267Ab2FNInm (ORCPT ); Thu, 14 Jun 2012 04:43:42 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:46684 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753478Ab2FNInk (ORCPT ); Thu, 14 Jun 2012 04:43:40 -0400 Date: Thu, 14 Jun 2012 10:43:32 +0200 From: Johannes Weiner To: kosaki.motohiro@gmail.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, KOSAKI Motohiro , Nick Piggin , Michal Hocko , Mel Gorman , KAMEZAWA Hiroyuki , Minchan Kim Subject: Re: [resend][PATCH] mm, vmscan: fix do_try_to_free_pages() livelock Message-ID: <20120614084332.GN1761@cmpxchg.org> References: <1339661592-3915-1-git-send-email-kosaki.motohiro@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1339661592-3915-1-git-send-email-kosaki.motohiro@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2785 Lines: 64 On Thu, Jun 14, 2012 at 04:13:12AM -0400, kosaki.motohiro@gmail.com wrote: > From: KOSAKI Motohiro > > 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. > > We can't turn on zone->all_unreclaimable from direct reclaim path > because direct reclaim path don't take any lock and this way is racy. > > Thus this patch removes zone->all_unreclaimable field completely and > recalculates zone reclaimable state every time. > > Note: we can't take the idea that direct-reclaim see zone->pages_scanned > directly and kswapd continue to use zone->all_unreclaimable. Because, it > is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use > zone->all_unreclaimable as a name) describes the detail. > > Reported-by: Aaditya Kumar > Reported-by: Ying Han > Cc: Nick Piggin > Acked-by: Rik van Riel > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Mel Gorman > Cc: KAMEZAWA Hiroyuki > Cc: Minchan Kim > Signed-off-by: KOSAKI Motohiro Acked-by: Johannes Weiner > @@ -2497,12 +2490,11 @@ loop_again: > shrink_zone(zone, &sc); > > reclaim_state->reclaimed_slab = 0; > - nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); > + shrink_slab(&shrink, sc.nr_scanned, lru_pages); > sc.nr_reclaimed += reclaim_state->reclaimed_slab; > total_scanned += sc.nr_scanned; > > - if (nr_slab == 0 && !zone_reclaimable(zone)) > - zone->all_unreclaimable = 1; > + That IS a slight change in behaviour. But then, if you scanned 6 times the amount of reclaimable pages without freeing a single slab page, it's probably not worth going on. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/