From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752006Ab2KPLXp (ORCPT ); Fri, 16 Nov 2012 06:23:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:33171 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751883Ab2KPLXn (ORCPT ); Fri, 16 Nov 2012 06:23:43 -0500 From: Mel Gorman To: Peter Zijlstra , Andrea Arcangeli , Ingo Molnar Cc: Rik van Riel , Johannes Weiner , Hugh Dickins , Thomas Gleixner , Linus Torvalds , Andrew Morton , Linux-MM , LKML , Mel Gorman Subject: [PATCH 32/43] mm: numa: Use a two-stage filter to restrict pages being migrated for unlikely task<->node relationships Date: Fri, 16 Nov 2012 11:22:42 +0000 Message-Id: <1353064973-26082-33-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.7.9.2 In-Reply-To: <1353064973-26082-1-git-send-email-mgorman@suse.de> References: <1353064973-26082-1-git-send-email-mgorman@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org While it is desirable that all threads in a process run on its home node, this is not always possible or necessary. There may be more threads than exist within the node or the node might over-subscribed with unrelated processes. This can cause a situation whereby a page gets migrated off its home node because the threads clearing pte_numa were running off-node. This patch uses page->last_nid to build a two-stage filter before pages get migrated to avoid problems with short or unlikely task<->node relationships. Signed-off-by: Mel Gorman --- mm/mempolicy.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 7acc97b..648423a 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2453,9 +2453,37 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long } /* Migrate the page towards the node whose CPU is referencing it */ - if (pol->flags & MPOL_F_MORON) + if (pol->flags & MPOL_F_MORON) { + int last_nid; + polnid = numa_node_id(); + /* + * Multi-stage node selection is used in conjunction + * with a periodic migration fault to build a temporal + * task<->page relation. By using a two-stage filter we + * remove short/unlikely relations. + * + * Using P(p) ~ n_p / n_t as per frequentist + * probability, we can equate a task's usage of a + * particular page (n_p) per total usage of this + * page (n_t) (in a given time-span) to a probability. + * + * Our periodic faults will sample this probability and + * getting the same result twice in a row, given these + * samples are fully independent, is then given by + * P(n)^2, provided our sample period is sufficiently + * short compared to the usage pattern. + * + * This quadric squishes small probabilities, making + * it less likely we act on an unlikely task<->page + * relation. + */ + last_nid = page_xchg_last_nid(page, polnid); + if (last_nid != polnid) + goto out; + } + if (curnid != polnid) ret = polnid; out: -- 1.7.9.2