Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763260AbZFKLhY (ORCPT ); Thu, 11 Jun 2009 07:37:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758634AbZFKLhJ (ORCPT ); Thu, 11 Jun 2009 07:37:09 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:45857 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755158AbZFKLhH (ORCPT ); Thu, 11 Jun 2009 07:37:07 -0400 From: KOSAKI Motohiro To: Mel Gorman Subject: Re: [PATCH 1/3] Properly account for the number of page cache pages zone_reclaim() can reclaim Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton , Rik van Riel , Christoph Lameter , Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML In-Reply-To: <1244717273-15176-2-git-send-email-mel@csn.ul.ie> References: <1244717273-15176-1-git-send-email-mel@csn.ul.ie> <1244717273-15176-2-git-send-email-mel@csn.ul.ie> Message-Id: <20090611203349.6D68.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 11 Jun 2009 20:37:04 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6729 Lines: 167 > On NUMA machines, the administrator can configure zone_reclaim_mode that > is a more targetted form of direct reclaim. On machines with large NUMA > distances for example, a zone_reclaim_mode defaults to 1 meaning that clean > unmapped pages will be reclaimed if the zone watermarks are not being met. > > There is a heuristic that determines if the scan is worthwhile but the problem > is that the heuristic is not being properly applied and is basically assuming > zone_reclaim_mode is 1 if it is enabled. The lack of proper detection can > manfiest as high CPU usage as the LRU list is scanned uselessly. > > Historically, once enabled it was depending on NR_FILE_PAGES which may > include swapcache pages that the reclaim_mode cannot deal with. Patch > vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim.patch by > Kosaki Motohiro noted that zone_page_state(zone, NR_FILE_PAGES) included > pages that were not file-backed such as swapcache and made a calculation > based on the inactive, active and mapped files. This is far superior > when zone_reclaim==1 but if RECLAIM_SWAP is set, then NR_FILE_PAGES is a > reasonable starting figure. > > This patch alters how zone_reclaim() works out how many pages it might be > able to reclaim given the current reclaim_mode. If RECLAIM_SWAP is set > in the reclaim_mode it will either consider NR_FILE_PAGES as potential > candidates or else use NR_{IN}ACTIVE}_PAGES-NR_FILE_MAPPED to discount > swapcache and other non-file-backed pages. If RECLAIM_WRITE is not set, > then NR_FILE_DIRTY number of pages are not candidates. If RECLAIM_SWAP is > not set, then NR_FILE_MAPPED are not. > > [mmotm note: This patch should be merged with or replace > vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim. Kosaki?] > > [kosaki.motohiro@jp.fujitsu.com: Estimate unmapped pages minus tmpfs pages] > [fengguang.wu@intel.com: Fix underflow problem in Kosaki's estimate] > Signed-off-by: Mel Gorman > Reviewed-by: Rik van Riel > Acked-by: Christoph Lameter > --- > mm/vmscan.c | 55 +++++++++++++++++++++++++++++++++++++++++-------------- > 1 files changed, 41 insertions(+), 14 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 2ddcfc8..d832ba8 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2333,6 +2333,44 @@ int sysctl_min_unmapped_ratio = 1; > */ > int sysctl_min_slab_ratio = 5; > > +static inline unsigned long zone_unmapped_file_pages(struct zone *zone) > +{ > + unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); > + unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + > + zone_page_state(zone, NR_ACTIVE_FILE); > + > + /* > + * It's possible for there to be more file mapped pages than > + * accounted for by the pages on the file LRU lists because > + * tmpfs pages accounted for as ANON can also be FILE_MAPPED > + */ > + return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; > +} > + > +/* Work out how many page cache pages we can reclaim in this reclaim_mode */ > +static long zone_pagecache_reclaimable(struct zone *zone) > +{ > + long nr_pagecache_reclaimable; > + long delta = 0; > + > + /* > + * If RECLAIM_SWAP is set, then all file pages are considered > + * potentially reclaimable. Otherwise, we have to worry about > + * pages like swapcache and zone_unmapped_file_pages() provides > + * a better estimate > + */ > + if (zone_reclaim_mode & RECLAIM_SWAP) > + nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); > + else > + nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); > + > + /* If we can't clean pages, remove dirty pages from consideration */ > + if (!(zone_reclaim_mode & RECLAIM_WRITE)) > + delta += zone_page_state(zone, NR_FILE_DIRTY); no use delta? > + > + return nr_pagecache_reclaimable; > +} > + > /* > * Try to free up some pages from this zone through reclaim. > */ > @@ -2355,7 +2393,6 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > .isolate_pages = isolate_pages_global, > }; > unsigned long slab_reclaimable; > - long nr_unmapped_file_pages; > > disable_swap_token(); > cond_resched(); > @@ -2368,11 +2405,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > reclaim_state.reclaimed_slab = 0; > p->reclaim_state = &reclaim_state; > > - nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) + > - zone_page_state(zone, NR_ACTIVE_FILE) - > - zone_page_state(zone, NR_FILE_MAPPED); > - > - if (nr_unmapped_file_pages > zone->min_unmapped_pages) { > + if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { Documentation/sysctl/vm.txt says ============================================================= min_unmapped_ratio: This is available only on NUMA kernels. A percentage of the total pages in each zone. Zone reclaim will only occur if more than this percentage of pages are file backed and unmapped. This is to insure that a minimal amount of local pages is still available for file I/O even if the node is overallocated. The default is 1 percent. ============================================================== but your code condider more addional thing. Can you please change document too? > /* > * Free memory by calling shrink zone with increasing > * priorities until we have enough memory freed. > @@ -2419,8 +2452,6 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > { > int node_id; > int ret; > - long nr_unmapped_file_pages; > - long nr_slab_reclaimable; > > /* > * Zone reclaim reclaims unmapped file backed pages and > @@ -2432,12 +2463,8 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) > * if less than a specified percentage of the zone is used by > * unmapped file backed pages. > */ > - nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) + > - zone_page_state(zone, NR_ACTIVE_FILE) - > - zone_page_state(zone, NR_FILE_MAPPED); > - nr_slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE); > - if (nr_unmapped_file_pages <= zone->min_unmapped_pages && > - nr_slab_reclaimable <= zone->min_slab_pages) > + if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && > + zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) > return 0; > > if (zone_is_all_unreclaimable(zone)) > -- > 1.5.6.5 > -- 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/