Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753388AbbKXNH6 (ORCPT ); Tue, 24 Nov 2015 08:07:58 -0500 Received: from relay.parallels.com ([195.214.232.42]:36970 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752692AbbKXNH5 (ORCPT ); Tue, 24 Nov 2015 08:07:57 -0500 Date: Tue, 24 Nov 2015 16:07:40 +0300 From: Vladimir Davydov To: Michal Hocko CC: Andrew Morton , Johannes Weiner , Vlastimil Babka , Mel Gorman , , LKML , Michal Hocko Subject: Re: [PATCH 2/2] mm, vmscan: do not overestimate anonymous reclaimable pages Message-ID: <20151124130740.GG29014@esperanza> References: <1448366100-11023-1-git-send-email-mhocko@kernel.org> <1448366100-11023-3-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1448366100-11023-3-git-send-email-mhocko@kernel.org> X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To MSK-EXCH1.sw.swsoft.com (10.67.48.55) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2392 Lines: 62 On Tue, Nov 24, 2015 at 12:55:00PM +0100, Michal Hocko wrote: > zone_reclaimable_pages considers all anonymous pages on LRUs reclaimable > if there is at least one entry on the swap storage left. This can be > really misleading when the swap is short on space and skew reclaim > decisions based on zone_reclaimable_pages. Fix this by clamping the > number to the minimum of the available swap space and anon LRU pages. Suppose there's 100M of swap and 1G of anon pages. This patch makes zone_reclaimable_pages return 100M instead of 1G in this case. If you rotate 600M of oldest anon pages, which is quite possible, zone_reclaimable will start returning false, which is wrong, because there are still 400M pages that were not even scanned, besides those 600M of rotated pages could have become reclaimable after their ref bits got cleared. I think it is the name of zone_reclaimable_pages which is misleading. It should be called something like "zone_scannable_pages" judging by how it is used in zone_reclaimable. Thanks, Vladimir > > Signed-off-by: Michal Hocko > --- > mm/vmscan.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 946d348f5040..646001a1f279 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -195,15 +195,20 @@ static bool sane_reclaim(struct scan_control *sc) > static unsigned long zone_reclaimable_pages(struct zone *zone) > { > unsigned long nr; > + long nr_swap = get_nr_swap_pages(); > > nr = zone_page_state(zone, NR_ACTIVE_FILE) + > zone_page_state(zone, NR_INACTIVE_FILE) + > zone_page_state(zone, NR_ISOLATED_FILE); > > - if (get_nr_swap_pages() > 0) > - nr += zone_page_state(zone, NR_ACTIVE_ANON) + > - zone_page_state(zone, NR_INACTIVE_ANON) + > - zone_page_state(zone, NR_ISOLATED_ANON); > + if (nr_swap > 0) { > + unsigned long anon; > + > + anon = zone_page_state(zone, NR_ACTIVE_ANON) + > + zone_page_state(zone, NR_INACTIVE_ANON) + > + zone_page_state(zone, NR_ISOLATED_ANON); > + nr += min_t(unsigned long, nr_swap, anon); > + } > > return nr; > } -- 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/