From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id 7CF036B2BC3 for ; Thu, 22 Nov 2018 10:26:44 -0500 (EST) Received: by mail-qk1-f199.google.com with SMTP id w185so9556035qka.9 for ; Thu, 22 Nov 2018 07:26:44 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id b82si8566186qkb.56.2018.11.22.07.26.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Nov 2018 07:26:43 -0800 (PST) Subject: Re: [PATCH v2] mm, hotplug: move init_currently_empty_zone() under zone_span_lock protection References: <20181120014822.27968-1-richard.weiyang@gmail.com> <20181122101241.7965-1-richard.weiyang@gmail.com> From: David Hildenbrand Message-ID: <18088694-22c8-b09b-f500-4932b6199004@redhat.com> Date: Thu, 22 Nov 2018 16:26:40 +0100 MIME-Version: 1.0 In-Reply-To: <20181122101241.7965-1-richard.weiyang@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang , mhocko@suse.com, osalvador@suse.de Cc: akpm@linux-foundation.org, linux-mm@kvack.org On 22.11.18 11:12, 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. > > This patch is a preparation for removing the global lock during > online_pages phase. Also this patch changes the documentation of > node_size_lock to include the protectioin of nr_zones. I looked into locking recently, and there is more to it. Please read: commit dee6da22efac451d361f5224a60be2796d847b51 Author: David Hildenbrand Date: Tue Oct 30 15:10:44 2018 -0700 memory-hotplug.rst: add some details about locking internals Let's document the magic a bit, especially why device_hotplug_lock is required when adding/removing memory and how it all play together with requests to online/offline memory from user space. Short summary: Onlining/offlining of memory requires the device_hotplug_lock as of now. mem_hotplug_begin() is just an internal optimization. (we don't want everybody to take the device lock) > > Signed-off-by: Wei Yang > --- > v2: > * commit log changes > * modify the code in move_pfn_range_to_zone() instead of in > init_currently_empty_zone() > * 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 68d7b558924b..1bb749bee284 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -636,9 +636,10 @@ 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