From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753883AbdGNKsC (ORCPT ); Fri, 14 Jul 2017 06:48:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:33238 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753756AbdGNKsB (ORCPT ); Fri, 14 Jul 2017 06:48:01 -0400 Date: Fri, 14 Jul 2017 12:47:57 +0200 From: Michal Hocko To: Mel Gorman Cc: linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Vlastimil Babka , LKML , linux-api@vger.kernel.org Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Message-ID: <20170714104756.GD2618@dhcp22.suse.cz> References: <20170714080006.7250-1-mhocko@kernel.org> <20170714080006.7250-2-mhocko@kernel.org> <20170714093650.l67vbem2g4typkta@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170714093650.l67vbem2g4typkta@suse.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 14-07-17 10:36:50, Mel Gorman wrote: > On Fri, Jul 14, 2017 at 09:59:58AM +0200, Michal Hocko wrote: > > From: Michal Hocko > > > > Supporting zone ordered zonelists costs us just a lot of code while > > the usefulness is arguable if existent at all. Mel has already made > > node ordering default on 64b systems. 32b systems are still using > > ZONELIST_ORDER_ZONE because it is considered better to fallback to > > a different NUMA node rather than consume precious lowmem zones. > > > > This argument is, however, weaken by the fact that the memory reclaim > > has been reworked to be node rather than zone oriented. This means > > that lowmem requests have to skip over all highmem pages on LRUs already > > and so zone ordering doesn't save the reclaim time much. So the only > > advantage of the zone ordering is under a light memory pressure when > > highmem requests do not ever hit into lowmem zones and the lowmem > > pressure doesn't need to reclaim. > > > > Considering that 32b NUMA systems are rather suboptimal already and > > it is generally advisable to use 64b kernel on such a HW I believe we > > should rather care about the code maintainability and just get rid of > > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if > > somebody tries to set zone ordering either from kernel command line > > or the sysctl. > > > > Cc: > > Signed-off-by: Michal Hocko > > index 80e4adb4c360..d9f4ea057e74 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -4864,40 +4824,22 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write, > > void __user *buffer, size_t *length, > > loff_t *ppos) > > { > > - char saved_string[NUMA_ZONELIST_ORDER_LEN]; > > + char *str; > > int ret; > > - static DEFINE_MUTEX(zl_order_mutex); > > > > - mutex_lock(&zl_order_mutex); > > - if (write) { > > - if (strlen((char *)table->data) >= NUMA_ZONELIST_ORDER_LEN) { > > - ret = -EINVAL; > > - goto out; > > - } > > - strcpy(saved_string, (char *)table->data); > > + if (!write) { > > + int len = sizeof("Default"); > > + if (copy_to_user(buffer, "Default", len)) > > + return -EFAULT; > > + return len; > > } > > That should to be "default" because the original code would have the proc > entry display "default" unless it was set at runtime. Pretty weird I > know but it's always possible someone is parsing the original default > and not handling it properly. Ohh, right! That is indeed strange. Then I guess it would be probably better to simply return Node to make it clear what the default is. What do you think? > Otherwise I think we're way past the point where large memory 32-bit > NUMA machines are a thing so > > Acked-by: Mel Gorman Thanks! -- Michal Hocko SUSE Labs