From: Michal Hocko <mhocko@kernel.org> To: Mel Gorman <mgorman@suse.de> Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Vlastimil Babka <vbabka@suse.cz>, LKML <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Date: Fri, 14 Jul 2017 12:47:57 +0200 Message-ID: <20170714104756.GD2618@dhcp22.suse.cz> (raw) In-Reply-To: <20170714093650.l67vbem2g4typkta@suse.de> 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 <mhocko@suse.com> > > > > 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: <linux-api@vger.kernel.org> > > Signed-off-by: Michal Hocko <mhocko@suse.com> > > 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 <mgorman@suse.de> Thanks! -- Michal Hocko SUSE Labs -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply index Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-07-14 7:59 [PATCH 0/9] cleanup zonelists initialization Michal Hocko 2017-07-14 7:59 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko 2017-07-14 9:36 ` Mel Gorman 2017-07-14 10:47 ` Michal Hocko [this message] 2017-07-14 11:16 ` Mel Gorman 2017-07-14 11:38 ` Michal Hocko 2017-07-14 12:56 ` Mel Gorman 2017-07-14 13:01 ` Mel Gorman 2017-07-14 13:08 ` Michal Hocko 2017-07-19 9:33 ` Vlastimil Babka 2017-07-19 13:44 ` Michal Hocko 2017-07-14 7:59 ` [PATCH 2/9] mm, page_alloc: remove boot pageset initialization from memory hotplug Michal Hocko 2017-07-14 9:39 ` Mel Gorman 2017-07-19 13:15 ` Vlastimil Babka 2017-07-14 8:00 ` [PATCH 3/9] mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization Michal Hocko 2017-07-14 9:48 ` Mel Gorman 2017-07-14 10:50 ` Michal Hocko 2017-07-14 12:32 ` Mel Gorman 2017-07-14 12:39 ` Michal Hocko 2017-07-14 12:56 ` Mel Gorman 2017-07-19 13:19 ` Vlastimil Babka 2017-07-14 8:00 ` [PATCH 4/9] mm, memory_hotplug: drop zone from build_all_zonelists Michal Hocko 2017-07-19 13:33 ` Vlastimil Babka 2017-07-20 8:15 ` Michal Hocko 2017-07-14 8:00 ` [PATCH 5/9] mm, memory_hotplug: remove explicit build_all_zonelists from try_online_node Michal Hocko 2017-07-14 12:14 ` Michal Hocko 2017-07-20 6:13 ` Vlastimil Babka 2017-07-14 8:00 ` [PATCH 6/9] mm, page_alloc: simplify zonelist initialization Michal Hocko 2017-07-14 9:55 ` Mel Gorman 2017-07-14 10:51 ` Michal Hocko 2017-07-14 12:46 ` Mel Gorman 2017-07-14 13:02 ` Michal Hocko 2017-07-14 14:18 ` Mel Gorman 2017-07-17 6:06 ` Michal Hocko 2017-07-17 8:07 ` Mel Gorman 2017-07-17 8:19 ` Michal Hocko 2017-07-17 8:58 ` Mel Gorman 2017-07-17 9:15 ` Michal Hocko 2017-07-20 6:55 ` Vlastimil Babka 2017-07-20 7:19 ` Michal Hocko 2017-07-14 8:00 ` [PATCH 7/9] mm, page_alloc: remove stop_machine from build_all_zonelists Michal Hocko 2017-07-14 9:59 ` Mel Gorman 2017-07-14 11:00 ` Michal Hocko 2017-07-14 12:47 ` Mel Gorman 2017-07-14 11:29 ` Vlastimil Babka 2017-07-14 11:43 ` Michal Hocko 2017-07-14 11:45 ` Michal Hocko 2017-07-20 6:16 ` Vlastimil Babka 2017-07-20 7:24 ` Vlastimil Babka 2017-07-20 9:21 ` Michal Hocko 2017-07-14 8:00 ` [PATCH 8/9] mm, memory_hotplug: get rid of zonelists_mutex Michal Hocko 2017-07-14 8:00 ` [PATCH 9/9] mm, sparse, page_ext: drop ugly N_HIGH_MEMORY branches for allocations Michal Hocko 2017-07-20 8:04 ` Vlastimil Babka 2017-07-21 14:39 [PATCH -v1 0/9] cleanup zonelists initialization Michal Hocko 2017-07-21 14:39 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko 2017-07-21 14:45 ` Michal Hocko
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