Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933491AbZFLKRp (ORCPT ); Fri, 12 Jun 2009 06:17:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762283AbZFLKRh (ORCPT ); Fri, 12 Jun 2009 06:17:37 -0400 Received: from gir.skynet.ie ([193.1.99.77]:50073 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760282AbZFLKRg (ORCPT ); Fri, 12 Jun 2009 06:17:36 -0400 Date: Fri, 12 Jun 2009 11:17:35 +0100 From: Mel Gorman To: KOSAKI Motohiro Cc: Andrew Morton , Rik van Riel , Christoph Lameter , Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML Subject: Re: [PATCH 1/3] Properly account for the number of page cache pages zone_reclaim() can reclaim Message-ID: <20090612101735.GA14498@csn.ul.ie> References: <1244717273-15176-1-git-send-email-mel@csn.ul.ie> <1244717273-15176-2-git-send-email-mel@csn.ul.ie> <20090611203349.6D68.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090611203349.6D68.A69D9226@jp.fujitsu.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8227 Lines: 199 On Thu, Jun 11, 2009 at 08:37:04PM +0900, KOSAKI Motohiro wrote: > > 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? > delta was used twice in an interim version when it was possible to overflow the counter. I left it as is because if another counter is added that must be subtracted from nr_pagecache_reclaimable, it'll be tidier to patch in if delta was there. I can take it out if you prefer. > > + > > + 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? > How does this look? ============================================================== min_unmapped_ratio: This is available only on NUMA kernels. This is a percentage of the total pages in each zone. Zone reclaim will only occur if more than this percentage are in a state that zone_reclaim_mode allows to be reclaimed. If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared against all file-backed unmapped pages including swapcache pages and tmpfs files. Otherwise, only unmapped pages backed by normal files but not tmpfs files and similar are considered. The default is 1 percent. ============================================================== > > > /* > > * 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 > > > > > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/