From: Oscar Salvador <osalvador@techadventures.net> To: Michal Hocko <mhocko@kernel.org> Cc: pavel.tatashin@microsoft.com, linux-nvdimm@lists.01.org, dave.hansen@intel.com, linux-kernel@vger.kernel.org, mingo@kernel.org, linux-mm@kvack.org, jglisse@redhat.com, rppt@linux.vnet.ibm.com, kirill.shutemov@linux.intel.com, Alexander Duyck <alexander.h.duyck@linux.intel.com>, akpm@linux-foundation.org Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Date: Fri, 28 Sep 2018 10:12:24 +0200 [thread overview] Message-ID: <20180928081224.GA25561@techadventures.net> (raw) In-Reply-To: <20180927131329.GI6278@dhcp22.suse.cz> On Thu, Sep 27, 2018 at 03:13:29PM +0200, Michal Hocko wrote: > I would have to double check but is the hotplug lock really serializing > access to the state initialized by init_currently_empty_zone? E.g. > zone_start_pfn is a nice example of a state that is used outside of the > lock. zone's free lists are similar. So do we really need the hoptlug > lock? And more broadly, what does the hotplug lock is supposed to > serialize in general. A proper documentation would surely help to answer > these questions. There is way too much of "do not touch this code and > just make my particular hack" mindset which made the whole memory > hotplug a giant pile of mess. We really should start with some proper > engineering here finally. * Locking rules: * * zone_start_pfn and spanned_pages are protected by span_seqlock. * It is a seqlock because it has to be read outside of zone->lock, * and it is done in the main allocator path. But, it is written * quite infrequently. * * Write access to present_pages at runtime should be protected by * mem_hotplug_begin/end(). Any reader who can't tolerant drift of * present_pages should get_online_mems() to get a stable value. IIUC, looks like zone_start_pfn should be envolved with zone_span_writelock/zone_span_writeunlock, and since zone_start_pfn is changed in init_currently_empty_zone, I guess that the whole function should be within that lock. So, a blind shot, but could we do something like the following? diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 898e1f816821..49f87252f1b1 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -764,14 +764,13 @@ 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); Then, we could take move_pfn_range_to_zone out of the hotplug lock. Although I am not sure about leaving memmap_init_zone unprotected. For the normal memory, that is not a problem since the memblock's lock protects us from touching the same pages at the same time in online/offline_pages, but for HMM/devm the story is different. I am totally unaware of HMM/devm, so I am not sure if its protected somehow. e.g: what happens if devm_memremap_pages and devm_memremap_pages_release are running at the same time for the same memory-range (with the assumption that the hotplug-lock does not protect move_pfn_range_to_zone anymore). -- Oscar Salvador SUSE L3 _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm
WARNING: multiple messages have this Message-ID (diff)
From: Oscar Salvador <osalvador@techadventures.net> To: Michal Hocko <mhocko@kernel.org> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>, linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, pavel.tatashin@microsoft.com, dave.jiang@intel.com, dave.hansen@intel.com, jglisse@redhat.com, rppt@linux.vnet.ibm.com, dan.j.williams@intel.com, logang@deltatee.com, mingo@kernel.org, kirill.shutemov@linux.intel.com Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Date: Fri, 28 Sep 2018 10:12:24 +0200 [thread overview] Message-ID: <20180928081224.GA25561@techadventures.net> (raw) In-Reply-To: <20180927131329.GI6278@dhcp22.suse.cz> On Thu, Sep 27, 2018 at 03:13:29PM +0200, Michal Hocko wrote: > I would have to double check but is the hotplug lock really serializing > access to the state initialized by init_currently_empty_zone? E.g. > zone_start_pfn is a nice example of a state that is used outside of the > lock. zone's free lists are similar. So do we really need the hoptlug > lock? And more broadly, what does the hotplug lock is supposed to > serialize in general. A proper documentation would surely help to answer > these questions. There is way too much of "do not touch this code and > just make my particular hack" mindset which made the whole memory > hotplug a giant pile of mess. We really should start with some proper > engineering here finally. * Locking rules: * * zone_start_pfn and spanned_pages are protected by span_seqlock. * It is a seqlock because it has to be read outside of zone->lock, * and it is done in the main allocator path. But, it is written * quite infrequently. * * Write access to present_pages at runtime should be protected by * mem_hotplug_begin/end(). Any reader who can't tolerant drift of * present_pages should get_online_mems() to get a stable value. IIUC, looks like zone_start_pfn should be envolved with zone_span_writelock/zone_span_writeunlock, and since zone_start_pfn is changed in init_currently_empty_zone, I guess that the whole function should be within that lock. So, a blind shot, but could we do something like the following? diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 898e1f816821..49f87252f1b1 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -764,14 +764,13 @@ 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); Then, we could take move_pfn_range_to_zone out of the hotplug lock. Although I am not sure about leaving memmap_init_zone unprotected. For the normal memory, that is not a problem since the memblock's lock protects us from touching the same pages at the same time in online/offline_pages, but for HMM/devm the story is different. I am totally unaware of HMM/devm, so I am not sure if its protected somehow. e.g: what happens if devm_memremap_pages and devm_memremap_pages_release are running at the same time for the same memory-range (with the assumption that the hotplug-lock does not protect move_pfn_range_to_zone anymore). -- Oscar Salvador SUSE L3
next prev parent reply other threads:[~2018-09-28 8:12 UTC|newest] Thread overview: 144+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-09-25 20:18 [PATCH v5 0/4] Address issues slowing persistent memory initialization Alexander Duyck 2018-09-25 20:18 ` Alexander Duyck 2018-09-25 20:19 ` [PATCH v5 1/4] mm: Remove now defunct NO_BOOTMEM from depends list for deferred init Alexander Duyck 2018-09-25 20:19 ` Alexander Duyck 2018-09-25 21:05 ` Mike Rapoport 2018-09-25 21:05 ` Mike Rapoport 2018-09-25 20:20 ` [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning Alexander Duyck 2018-09-25 20:20 ` Alexander Duyck 2018-09-25 20:26 ` Dave Hansen 2018-09-25 20:26 ` Dave Hansen 2018-09-25 20:38 ` Alexander Duyck 2018-09-25 20:38 ` Alexander Duyck 2018-09-25 22:14 ` Dave Hansen 2018-09-25 22:14 ` Dave Hansen 2018-09-25 22:14 ` Dave Hansen 2018-09-25 22:27 ` Alexander Duyck 2018-09-25 22:27 ` Alexander Duyck 2018-09-25 22:27 ` Alexander Duyck 2018-09-26 7:38 ` Michal Hocko 2018-09-26 7:38 ` Michal Hocko 2018-09-26 15:24 ` Alexander Duyck 2018-09-26 15:39 ` Michal Hocko 2018-09-26 15:39 ` Michal Hocko 2018-09-26 15:41 ` Dave Hansen 2018-09-26 15:41 ` Dave Hansen 2018-09-26 16:18 ` Alexander Duyck 2018-09-26 15:36 ` Dave Hansen 2018-09-26 22:36 ` Andrew Morton 2018-09-26 22:36 ` Andrew Morton 2018-09-25 20:20 ` [PATCH v5 3/4] mm: Create non-atomic version of SetPageReserved for init use Alexander Duyck 2018-09-25 20:20 ` Alexander Duyck 2018-09-25 20:21 ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Alexander Duyck 2018-09-25 20:21 ` Alexander Duyck 2018-09-26 7:55 ` Michal Hocko 2018-09-26 18:25 ` Alexander Duyck 2018-09-26 18:25 ` Alexander Duyck 2018-09-26 18:52 ` Dan Williams 2018-09-26 18:52 ` Dan Williams 2018-09-27 11:20 ` Michal Hocko 2018-09-27 11:20 ` Michal Hocko 2018-09-27 11:09 ` Michal Hocko 2018-09-27 11:09 ` Michal Hocko 2018-09-27 12:25 ` Oscar Salvador 2018-09-27 13:13 ` Michal Hocko 2018-09-27 14:50 ` Oscar Salvador 2018-09-27 14:50 ` Oscar Salvador 2018-09-27 14:50 ` Oscar Salvador 2018-09-27 15:41 ` David Hildenbrand 2018-09-27 15:41 ` David Hildenbrand 2018-09-28 8:12 ` Oscar Salvador [this message] 2018-09-28 8:12 ` Oscar Salvador 2018-09-28 8:44 ` Oscar Salvador 2018-09-28 8:44 ` Oscar Salvador 2018-09-28 15:50 ` Dan Williams 2018-09-28 15:50 ` Dan Williams 2018-09-27 12:32 ` Oscar Salvador 2018-10-08 21:01 ` Dan Williams 2018-10-08 21:01 ` Dan Williams 2018-10-08 21:38 ` Alexander Duyck 2018-10-08 21:38 ` Alexander Duyck 2018-10-08 22:00 ` Dan Williams 2018-10-08 22:00 ` Dan Williams 2018-10-08 22:00 ` Dan Williams 2018-10-08 22:07 ` Alexander Duyck 2018-10-08 22:07 ` Alexander Duyck 2018-10-08 22:36 ` Alexander Duyck 2018-10-08 22:36 ` Alexander Duyck 2018-10-08 22:59 ` Dan Williams 2018-10-08 23:34 ` [mm PATCH] memremap: Fix reference count for pgmap in devm_memremap_pages Alexander Duyck 2018-10-08 23:34 ` Alexander Duyck 2018-10-09 0:20 ` Dan Williams 2018-10-09 0:20 ` Dan Williams 2018-10-09 17:00 ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Yi Zhang 2018-10-09 17:00 ` Yi Zhang 2018-10-09 18:04 ` Dan Williams 2018-10-09 18:04 ` Dan Williams 2018-10-09 20:26 ` Alexander Duyck 2018-10-09 20:26 ` Alexander Duyck 2018-10-09 21:19 ` Dan Williams 2018-10-09 21:19 ` Dan Williams 2018-10-10 12:52 ` Yi Zhang 2018-10-10 12:52 ` Yi Zhang 2018-10-10 15:27 ` Alexander Duyck 2018-10-10 15:27 ` Alexander Duyck 2018-10-11 8:17 ` Yi Zhang 2018-10-11 8:17 ` Yi Zhang 2018-10-10 9:58 ` Michal Hocko 2018-10-10 16:39 ` Alexander Duyck 2018-10-10 16:39 ` Alexander Duyck 2018-10-10 17:24 ` Michal Hocko 2018-10-10 17:24 ` Michal Hocko 2018-10-10 17:39 ` Alexander Duyck 2018-10-10 17:39 ` Alexander Duyck 2018-10-10 17:53 ` Michal Hocko 2018-10-10 17:53 ` Michal Hocko 2018-10-10 18:13 ` Alexander Duyck 2018-10-10 18:13 ` Alexander Duyck 2018-10-10 18:52 ` Michal Hocko 2018-10-10 18:52 ` Michal Hocko 2018-10-11 8:55 ` Michal Hocko 2018-10-11 8:55 ` Michal Hocko 2018-10-11 17:38 ` Alexander Duyck 2018-10-11 18:22 ` Dan Williams 2018-10-11 18:22 ` Dan Williams 2018-10-17 7:52 ` Michal Hocko 2018-10-17 7:52 ` Michal Hocko 2018-10-17 15:02 ` Alexander Duyck 2018-10-17 15:02 ` Alexander Duyck 2018-10-29 14:12 ` Michal Hocko 2018-10-29 14:12 ` Michal Hocko 2018-10-29 15:59 ` Alexander Duyck 2018-10-29 15:59 ` Alexander Duyck 2018-10-29 15:59 ` Alexander Duyck 2018-10-29 16:35 ` Michal Hocko 2018-10-29 16:35 ` Michal Hocko 2018-10-29 17:01 ` Alexander Duyck 2018-10-29 17:24 ` Michal Hocko 2018-10-29 17:24 ` Michal Hocko 2018-10-29 17:34 ` Dan Williams 2018-10-29 17:34 ` Dan Williams 2018-10-29 17:45 ` Michal Hocko 2018-10-29 17:45 ` Michal Hocko 2018-10-29 17:42 ` Alexander Duyck 2018-10-29 17:42 ` Alexander Duyck 2018-10-29 18:18 ` Michal Hocko 2018-10-29 18:18 ` Michal Hocko 2018-10-29 19:59 ` Alexander Duyck 2018-10-29 19:59 ` Alexander Duyck 2018-10-30 6:29 ` Michal Hocko 2018-10-30 6:29 ` Michal Hocko 2018-10-30 6:55 ` Dan Williams 2018-10-30 8:17 ` Michal Hocko 2018-10-30 8:17 ` Michal Hocko 2018-10-30 15:57 ` Dan Williams 2018-10-30 8:05 ` Oscar Salvador 2018-10-29 15:49 ` Dan Williams 2018-10-29 15:49 ` Dan Williams 2018-10-29 15:56 ` Michal Hocko 2018-10-10 18:18 ` Dan Williams 2018-10-10 18:18 ` Dan Williams 2018-10-11 8:39 ` Yi Zhang 2018-10-11 8:39 ` Yi Zhang 2018-10-11 15:38 ` Alexander Duyck 2018-10-11 15:38 ` Alexander Duyck
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