From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx202.postini.com [74.125.245.202]) by kanga.kvack.org (Postfix) with SMTP id A244B6B0044 for ; Tue, 6 Nov 2012 14:52:36 -0500 (EST) Message-ID: <50996B1A.7040601@redhat.com> Date: Tue, 06 Nov 2012 14:55:06 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 16/19] mm: numa: Add pte updates, hinting and migration stats References: <1352193295-26815-1-git-send-email-mgorman@suse.de> <1352193295-26815-17-git-send-email-mgorman@suse.de> In-Reply-To: <1352193295-26815-17-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Peter Zijlstra , Andrea Arcangeli , Ingo Molnar , Johannes Weiner , Hugh Dickins , Thomas Gleixner , Linus Torvalds , Andrew Morton , Linux-MM , LKML On 11/06/2012 04:14 AM, Mel Gorman wrote: > It is tricky to quantify the basic cost of automatic NUMA placement in a > meaningful manner. This patch adds some vmstats that can be used as part > of a basic costing model. > > u = basic unit = sizeof(void *) > Ca = cost of struct page access = sizeof(struct page) / u > Cpte = Cost PTE access = Ca > Cupdate = Cost PTE update = (2 * Cpte) + (2 * Wlock) > where Cpte is incurred twice for a read and a write and Wlock > is a constant representing the cost of taking or releasing a > lock > Cnumahint = Cost of a minor page fault = some high constant e.g. 1000 > Cpagerw = Cost to read or write a full page = Ca + PAGE_SIZE/u > Ci = Cost of page isolation = Ca + Wi > where Wi is a constant that should reflect the approximate cost > of the locking operation > Cpagecopy = Cpagerw + (Cpagerw * Wnuma) + Ci + (Ci * Wnuma) > where Wnuma is the approximate NUMA factor. 1 is local. 1.2 > would imply that remote accesses are 20% more expensive > > Balancing cost = Cpte * numa_pte_updates + > Cnumahint * numa_hint_faults + > Ci * numa_pages_migrated + > Cpagecopy * numa_pages_migrated > > Note that numa_pages_migrated is used as a measure of how many pages > were isolated even though it would miss pages that failed to migrate. A > vmstat counter could have been added for it but the isolation cost is > pretty marginal in comparison to the overall cost so it seemed overkill. > > The ideal way to measure automatic placement benefit would be to count > the number of remote accesses versus local accesses and do something like > > benefit = (remote_accesses_before - remove_access_after) * Wnuma > > but the information is not readily available. As a workload converges, the > expection would be that the number of remote numa hints would reduce to 0. > > convergence = numa_hint_faults_local / numa_hint_faults > where this is measured for the last N number of > numa hints recorded. When the workload is fully > converged the value is 1. > > This can measure if the placement policy is converging and how fast it is > doing it. > > Signed-off-by: Mel Gorman I'm skipping the ACKing of the policy patches, which appear to be meant to be placeholders for a "real" policy. However, you have a few more mechanism patches left in the series, which would be required regardless of what policy gets merged, so ... Reviewed-by: Rik van Riel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org