Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757904Ab2EKIfL (ORCPT ); Fri, 11 May 2012 04:35:11 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:49481 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757074Ab2EKIfC (ORCPT ); Fri, 11 May 2012 04:35:02 -0400 MIME-Version: 1.0 Date: Fri, 11 May 2012 14:05:01 +0530 Message-ID: Subject: [RFC][PATCH] mm: Update zone->un_reclaimable in direct reclaim path From: Aaditya Kumar To: linux-kernel@vger.kernel.org, kosaki.motohiro@gmail.com Cc: frank.rowand@am.sony.com, tim.bird@am.sony.com, takuzo.ohara@ap.sony.com, kan.iibuchi@jp.sony.com, kosaki.motohiro@jp.fujitsu.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3307 Lines: 98 Dear All, Commit 929bea7c714220fc76ce3f75bef9056477c28e74 seems to have broken the OOM invocation during memory hot unplug in low memory conditions. This commit modifies the 'un-reclaimabilty check' for giving up trying to reclaim pages in the direct reclaim path and invoke OOM killer to be based on zone->unreclaimable. While doing memory offline, if the memory to be off lined spans almost all the node then the memory needed to migrate pages for off lining can not be allocated from the node that is being off lined as all pages are now in ISOLATED state (and also free). Since most pages are would be free due to pages having been migrated, kswapd would not balance the zones as all zone watermarks would be OK and so zone->un_reclaimable flag which is currently only set by kswapd will NOT be set. If page allocator has been passed the zones from above node(being offlined) then OOM killer will never be invoked for low memory conditions because buddy allocator will not allocate ISOLATED pages and direct reclaim path will not give up trying because zone->unreclaimable flag would not be set for zone(s) in node being off lined and thus resulting in a system hang. The above issue is reproducible when off lining memory in low memory conditions on ARM systems for Cortex-A9, but the issue should be architecture independent. This patch fixes this BUG by updating zone->unreclaimable in direct reclaim path also. --- mm/vmscan.c | 11 8 + 3 - 0 ! 1 file changed, 8 insertions(+), 3 deletions(-) Index: b/mm/vmscan.c =================================================================== --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1997,7 +1997,7 @@ restart: * scan then give up on it. */ static void shrink_zones(int priority, struct zonelist *zonelist, - struct scan_control *sc) + struct scan_control *sc, int prev_nr_slab) { struct zoneref *z; struct zone *zone; @@ -2033,6 +2033,8 @@ static void shrink_zones(int priority, s } shrink_zone(priority, zone, sc); + if (prev_nr_slab == 0 && !zone_reclaimable(zone)) + zone->all_unreclaimable = 1; } } @@ -2091,6 +2093,7 @@ static unsigned long do_try_to_free_page struct zoneref *z; struct zone *zone; unsigned long writeback_threshold; + int prev_nr_slab = 1; get_mems_allowed(); delayacct_freepages_start(); @@ -2102,7 +2105,9 @@ static unsigned long do_try_to_free_page sc->nr_scanned = 0; if (!priority) disable_swap_token(sc->mem_cgroup); - shrink_zones(priority, zonelist, sc); + shrink_zones(priority, zonelist, sc, prev_nr_slab); + prev_nr_slab = 1; + /* * Don't shrink slabs when reclaiming memory from * over limit cgroups @@ -2117,7 +2122,7 @@ static unsigned long do_try_to_free_page lru_pages += zone_reclaimable_pages(zone); } - shrink_slab(shrink, sc->nr_scanned, lru_pages); + prev_nr_slab = shrink_slab(shrink, sc->nr_scanned, lru_pages); if (reclaim_state) { sc->nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; Regards, Aaditya Kumar. -- 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/