From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752619AbZH1M4J (ORCPT ); Fri, 28 Aug 2009 08:56:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752509AbZH1M4I (ORCPT ); Fri, 28 Aug 2009 08:56:08 -0400 Received: from gir.skynet.ie ([193.1.99.77]:58456 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752298AbZH1M4I (ORCPT ); Fri, 28 Aug 2009 08:56:08 -0400 Date: Fri, 28 Aug 2009 13:56:08 +0100 From: Mel Gorman To: Minchan Kim Cc: Andrew Morton , Linux Memory Management List , Christoph Lameter , Nick Piggin , Linux Kernel Mailing List Subject: Re: [PATCH 1/2] page-allocator: Split per-cpu list into one-list-per-migrate-type Message-ID: <20090828125559.GD5054@csn.ul.ie> References: <1251449067-3109-1-git-send-email-mel@csn.ul.ie> <1251449067-3109-2-git-send-email-mel@csn.ul.ie> <20090828205241.fc8dfa51.minchan.kim@barrios-desktop> <28c262360908280500tb47685btc9f36ca81605d55@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <28c262360908280500tb47685btc9f36ca81605d55@mail.gmail.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 On Fri, Aug 28, 2009 at 09:00:25PM +0900, Minchan Kim wrote: > On Fri, Aug 28, 2009 at 8:52 PM, Minchan Kim wrote: > > Hi, Mel. > > > > On Fri, 28 Aug 2009 09:44:26 +0100 > > Mel Gorman wrote: > > > >> Currently the per-cpu page allocator searches the PCP list for pages of the > >> correct migrate-type to reduce the possibility of pages being inappropriate > >> placed from a fragmentation perspective. This search is potentially expensive > >> in a fast-path and undesirable. Splitting the per-cpu list into multiple > >> lists increases the size of a per-cpu structure and this was potentially > >> a major problem at the time the search was introduced. These problem has > >> been mitigated as now only the necessary number of structures is allocated > >> for the running system. > >> > >> This patch replaces a list search in the per-cpu allocator with one list per > >> migrate type. The potential snag with this approach is when bulk freeing > >> pages. We round-robin free pages based on migrate type which has little > >> bearing on the cache hotness of the page and potentially checks empty lists > >> repeatedly in the event the majority of PCP pages are of one type. > >> > >> Signed-off-by: Mel Gorman > >> Acked-by: Nick Piggin > >> --- > >>  include/linux/mmzone.h |    5 ++- > >>  mm/page_alloc.c        |  106 ++++++++++++++++++++++++++--------------------- > >>  2 files changed, 63 insertions(+), 48 deletions(-) > >> > >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > >> index 008cdcd..045348f 100644 > >> --- a/include/linux/mmzone.h > >> +++ b/include/linux/mmzone.h > >> @@ -38,6 +38,7 @@ > >>  #define MIGRATE_UNMOVABLE     0 > >>  #define MIGRATE_RECLAIMABLE   1 > >>  #define MIGRATE_MOVABLE       2 > >> +#define MIGRATE_PCPTYPES      3 /* the number of types on the pcp lists */ > >>  #define MIGRATE_RESERVE       3 > >>  #define MIGRATE_ISOLATE       4 /* can't allocate from here */ > >>  #define MIGRATE_TYPES         5 > >> @@ -169,7 +170,9 @@ struct per_cpu_pages { > >>       int count;              /* number of pages in the list */ > >>       int high;               /* high watermark, emptying needed */ > >>       int batch;              /* chunk size for buddy add/remove */ > >> -     struct list_head list;  /* the list of pages */ > >> + > >> +     /* Lists of pages, one per migrate type stored on the pcp-lists */ > >> +     struct list_head lists[MIGRATE_PCPTYPES]; > >>  }; > >> > >>  struct per_cpu_pageset { > >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >> index ac3afe1..65eedb5 100644 > >> --- a/mm/page_alloc.c > >> +++ b/mm/page_alloc.c > >> @@ -522,7 +522,7 @@ static inline int free_pages_check(struct page *page) > >>  } > >> > >>  /* > >> - * Frees a list of pages. > >> + * Frees a number of pages from the PCP lists > >>   * Assumes all pages on list are in same zone, and of same order. > >>   * count is the number of pages to free. > >>   * > >> @@ -532,23 +532,36 @@ static inline int free_pages_check(struct page *page) > >>   * And clear the zone's pages_scanned counter, to hold off the "all pages are > >>   * pinned" detection logic. > >>   */ > >> -static void free_pages_bulk(struct zone *zone, int count, > >> -                                     struct list_head *list, int order) > >> +static void free_pcppages_bulk(struct zone *zone, int count, > >> +                                     struct per_cpu_pages *pcp) > >>  { > >> +     int migratetype = 0; > >> + > > > > How about caching the last sucess migratetype > > with 'per_cpu_pages->last_alloc_type'? > ^^^^ > free > > I think it could prevent a litte spinning empty list. > > Anyway, Ignore me. > I didn't see your next patch. > Nah, it's a reasonable suggestion. Patch 2 was one effort to reduce spinning but the comment was in patch 1 in case someone thought of something better. I tried what you suggested before but it didn't work out. For any sort of workload that varies the type of allocation (very frequent), it didn't reduce spinning significantly. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab