Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933520Ab3CUJyw (ORCPT ); Thu, 21 Mar 2013 05:54:52 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50674 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757950Ab3CUJyt (ORCPT ); Thu, 21 Mar 2013 05:54:49 -0400 Date: Thu, 21 Mar 2013 09:54:45 +0000 From: Mel Gorman To: Rik van Riel Cc: Linux-MM , Jiri Slaby , Valdis Kletnieks , Zlatko Calusic , Johannes Weiner , dormando , Satoru Moriya , Michal Hocko , LKML Subject: Re: [PATCH 02/10] mm: vmscan: Obey proportional scanning requirements for kswapd Message-ID: <20130321095444.GE1878@suse.de> References: <1363525456-10448-1-git-send-email-mgorman@suse.de> <1363525456-10448-3-git-send-email-mgorman@suse.de> <514A5E07.3080501@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <514A5E07.3080501@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3311 Lines: 99 On Wed, Mar 20, 2013 at 09:10:31PM -0400, Rik van Riel wrote: > On 03/17/2013 09:04 AM, Mel Gorman wrote: > >Simplistically, the anon and file LRU lists are scanned proportionally > >depending on the value of vm.swappiness although there are other factors > >taken into account by get_scan_count(). The patch "mm: vmscan: Limit > >the number of pages kswapd reclaims" limits the number of pages kswapd > >reclaims but it breaks this proportional scanning and may evenly shrink > >anon/file LRUs regardless of vm.swappiness. > > > >This patch preserves the proportional scanning and reclaim. It does mean > >that kswapd will reclaim more than requested but the number of pages will > >be related to the high watermark. > > > >Signed-off-by: Mel Gorman > >--- > > mm/vmscan.c | 52 +++++++++++++++++++++++++++++++++++++++++----------- > > 1 file changed, 41 insertions(+), 11 deletions(-) > > > >diff --git a/mm/vmscan.c b/mm/vmscan.c > >index 4835a7a..182ff15 100644 > >--- a/mm/vmscan.c > >+++ b/mm/vmscan.c > >@@ -1815,6 +1815,45 @@ out: > > } > > } > > > >+static void recalculate_scan_count(unsigned long nr_reclaimed, > >+ unsigned long nr_to_reclaim, > >+ unsigned long nr[NR_LRU_LISTS]) > >+{ > >+ enum lru_list l; > >+ > >+ /* > >+ * For direct reclaim, reclaim the number of pages requested. Less > >+ * care is taken to ensure that scanning for each LRU is properly > >+ * proportional. This is unfortunate and is improper aging but > >+ * minimises the amount of time a process is stalled. > >+ */ > >+ if (!current_is_kswapd()) { > >+ if (nr_reclaimed >= nr_to_reclaim) { > >+ for_each_evictable_lru(l) > >+ nr[l] = 0; > >+ } > >+ return; > >+ } > > This part is obvious. > > >+ /* > >+ * For kswapd, reclaim at least the number of pages requested. > >+ * However, ensure that LRUs shrink by the proportion requested > >+ * by get_scan_count() so vm.swappiness is obeyed. > >+ */ > >+ if (nr_reclaimed >= nr_to_reclaim) { > >+ unsigned long min = ULONG_MAX; > >+ > >+ /* Find the LRU with the fewest pages to reclaim */ > >+ for_each_evictable_lru(l) > >+ if (nr[l] < min) > >+ min = nr[l]; > >+ > >+ /* Normalise the scan counts so kswapd scans proportionally */ > >+ for_each_evictable_lru(l) > >+ nr[l] -= min; > >+ } > >+} > > This part took me a bit longer to get. > > Before getting to this point, we scanned the LRUs evenly. > By subtracting min from all of the LRUs, we end up stopping > the scanning of the LRU where we have the fewest pages left > to scan. > > This results in the scanning being concentrated where it > should be - on the LRUs where we have not done nearly > enough scanning yet. > This is exactly what my intention was. It does mean that we potentially reclaim much more than required by sc->nr_to_reclaim but I did not think of a straight-forward way around that that would work in every case. > However, I am not sure how to document it better than > your comment already has... > > Acked-by: Rik van Riel > Thanks. -- Mel Gorman SUSE Labs -- 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/