Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756025Ab3CUBL3 (ORCPT ); Wed, 20 Mar 2013 21:11:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23886 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753948Ab3CUBL2 (ORCPT ); Wed, 20 Mar 2013 21:11:28 -0400 Message-ID: <514A5E07.3080501@redhat.com> Date: Wed, 20 Mar 2013 21:10:31 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Mel Gorman 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 References: <1363525456-10448-1-git-send-email-mgorman@suse.de> <1363525456-10448-3-git-send-email-mgorman@suse.de> In-Reply-To: <1363525456-10448-3-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2915 Lines: 89 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. However, I am not sure how to document it better than your comment already has... Acked-by: Rik van Riel -- All rights reversed -- 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/