From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id D76CC6B5AFB for ; Fri, 30 Nov 2018 19:27:12 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id i55so3644800ede.14 for ; Fri, 30 Nov 2018 16:27:12 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id e44sor4181419ede.13.2018.11.30.16.27.11 for (Google Transport Security); Fri, 30 Nov 2018 16:27:11 -0800 (PST) Date: Sat, 1 Dec 2018 00:27:09 +0000 From: Wei Yang Subject: Re: [PATCH v3] mm, hotplug: move init_currently_empty_zone() under zone_span_lock protection Message-ID: <20181201002709.ggybtqza6c7hyqrn@master> Reply-To: Wei Yang References: <20181122101241.7965-1-richard.weiyang@gmail.com> <20181130065847.13714-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: Wei Yang , mhocko@suse.com, osalvador@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org On Fri, Nov 30, 2018 at 10:30:22AM +0100, David Hildenbrand wrote: >On 30.11.18 07:58, Wei Yang wrote: >> During online_pages phase, pgdat->nr_zones will be updated in case this >> zone is empty. >> >> Currently the online_pages phase is protected by the global lock >> mem_hotplug_begin(), which ensures there is no contention during the >> update of nr_zones. But this global lock introduces scalability issues. >> >> The patch moves init_currently_empty_zone under both zone_span_writelock >> and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >> and the zone's start_pfn. Also this patch changes the documentation >> of node_size_lock to include the protectioin of nr_zones. > >s/protectioin/protection/ > >> >> Signed-off-by: Wei Yang >> Acked-by: Michal Hocko >> Reviewed-by: Oscar Salvador >> CC: David Hildenbrand >> >> --- >> David, I may not catch you exact comment on the code or changelog. If I >> missed, just let me know. > >I guess I would have rewritten it to something like the following > >" >Currently the online_pages phase is protected by two global locks >(device_device_hotplug_lock and mem_hotplug_lock). Especial the latter >can result in scalability issues, as it will slow down code relying on >get_online_mems(). Let's prepare code for not having to rely on >get_online_mems() but instead some more fine grained locks. I am not sure why we specify get_online_mems() here. mem_hotplug_lock is grabed in many places besides this one. In my mind, each place introduce scalability issue, not only this one. Or you want to say, the mem_hotplug_lock will introduce scalability issue in two place: * hotplug process itself * slab allocation process The second one is more critical. And this is what we try to address? > >During online_pages phase, pgdat->nr_zones will be updated in case the >zone is empty. Right now mem_hotplug_lock ensures that there is no >contention during the update of nr_zones. > >The patch moves init_currently_empty_zone under both zone_span_writelock >and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >and the zone's start_pfn. Also this patch changes the documentation >of node_size_lock to include the protection of nr_zones. >" > >Does that make sense? > >> >> --- >> v3: >> * slightly modify the last paragraph of changelog based on Michal's >> comment >> v2: >> * commit log changes >> * modify the code in move_pfn_range_to_zone() instead of in >> init_currently_empty_zone() >> * pgdat_resize_lock documentation change >> --- >> include/linux/mmzone.h | 7 ++++--- >> mm/memory_hotplug.c | 5 ++--- >> 2 files changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >> index 3d0c472438d2..37d9c5c3faa6 100644 >> --- a/include/linux/mmzone.h >> +++ b/include/linux/mmzone.h >> @@ -635,9 +635,10 @@ typedef struct pglist_data { >> #endif >> #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) >> /* >> - * Must be held any time you expect node_start_pfn, node_present_pages >> - * or node_spanned_pages stay constant. Holding this will also >> - * guarantee that any pfn_valid() stays that way. >> + * Must be held any time you expect node_start_pfn, >> + * node_present_pages, node_spanned_pages or nr_zones stay constant. >> + * Holding this will also guarantee that any pfn_valid() stays that >> + * way. >> * >> * pgdat_resize_lock() and pgdat_resize_unlock() are provided to >> * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 61972da38d93..f626e7e5f57b 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -742,14 +742,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, >> int nid = pgdat->node_id; >> unsigned long flags; >> >> - if (zone_is_empty(zone)) >> - init_currently_empty_zone(zone, start_pfn, nr_pages); >> - >> clear_zone_contiguous(zone); >> >> /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ >> pgdat_resize_lock(pgdat, &flags); >> zone_span_writelock(zone); >> + if (zone_is_empty(zone)) >> + init_currently_empty_zone(zone, start_pfn, nr_pages); >> resize_zone_range(zone, start_pfn, nr_pages); >> zone_span_writeunlock(zone); >> resize_pgdat_range(pgdat, start_pfn, nr_pages); >> > > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me