From: Dan Williams <dan.j.williams@intel.com> To: alexander.h.duyck@linux.intel.com Cc: "Pasha Tatashin" <pavel.tatashin@microsoft.com>, linux-nvdimm <linux-nvdimm@lists.01.org>, "Dave Hansen" <dave.hansen@intel.com>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, "Michal Hocko" <mhocko@kernel.org>, "Linux MM" <linux-mm@kvack.org>, "Jérôme Glisse" <jglisse@redhat.com>, rppt@linux.vnet.ibm.com, "Andrew Morton" <akpm@linux-foundation.org>, "Ingo Molnar" <mingo@kernel.org>, "Kirill A. Shutemov" <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: Wed, 26 Sep 2018 11:52:56 -0700 [thread overview] Message-ID: <CAPcyv4iVnodai0bB74yeSCD2H+hoLsZYUk4sR9jV0pPAE+Zorw@mail.gmail.com> (raw) In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> On Wed, Sep 26, 2018 at 11:25 AM Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote: > > > > On 9/26/2018 12:55 AM, Michal Hocko wrote: > > On Tue 25-09-18 13:21:24, Alexander Duyck wrote: > >> The ZONE_DEVICE pages were being initialized in two locations. One was with > >> the memory_hotplug lock held and another was outside of that lock. The > >> problem with this is that it was nearly doubling the memory initialization > >> time. Instead of doing this twice, once while holding a global lock and > >> once without, I am opting to defer the initialization to the one outside of > >> the lock. This allows us to avoid serializing the overhead for memory init > >> and we can instead focus on per-node init times. > >> > >> One issue I encountered is that devm_memremap_pages and > >> hmm_devmmem_pages_create were initializing only the pgmap field the same > >> way. One wasn't initializing hmm_data, and the other was initializing it to > >> a poison value. Since this is something that is exposed to the driver in > >> the case of hmm I am opting for a third option and just initializing > >> hmm_data to 0 since this is going to be exposed to unknown third party > >> drivers. > > > > Why cannot you pull move_pfn_range_to_zone out of the hotplug lock? In > > other words why are you making zone device even more special in the > > generic hotplug code when it already has its own means to initialize the > > pfn range by calling move_pfn_range_to_zone. Not to mention the code > > duplication. > > So there were a few things I wasn't sure we could pull outside of the > hotplug lock. One specific example is the bits related to resizing the > pgdat and zone. I wanted to avoid pulling those bits outside of the > hotplug lock. > > The other bit that I left inside the hot-plug lock with this approach > was the initialization of the pages that contain the vmemmap. > > > That being said I really dislike this patch. > > In my mind this was a patch that "killed two birds with one stone". I > had two issues to address, the first one being the fact that we were > performing the memmap_init_zone while holding the hotplug lock, and the > other being the loop that was going through and initializing pgmap in > the hmm and memremap calls essentially added another 20 seconds > (measured for 3TB of memory per node) to the init time. With this patch > I was able to cut my init time per node by that 20 seconds, and then > made it so that we could scale as we added nodes as they could run in > parallel. Yeah, at the very least there is no reason for devm_memremap_pages() to do another loop through all pages, the core should handle this, but cleaning up the scope of the hotplug lock is needed. > With that said I am open to suggestions if you still feel like I need to > follow this up with some additional work. I just want to avoid > introducing any regressions in regards to functionality or performance. Could we push the hotplug lock deeper to the places that actually need it? What I found with my initial investigation is that we don't even need the hotplug lock for the vmemmap initialization with this patch [1]. Alternatively it seems the hotplug lock wants to synchronize changes to the zone and the page init work. If the hotplug lock was an rwsem the zone changes would be a write lock, but the init work could be done as a read lock to allow parallelism. I.e. still provide a sync point to be able to assert that no hotplug work is in-flight will holding the write lock, but otherwise allow threads that are touching independent parts of the memmap to run at the same time. [1]: https://patchwork.kernel.org/patch/10527229/ just focus on the mm/sparse-vmemmap.c changes at the end. _______________________________________________ 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: Dan Williams <dan.j.williams@intel.com> To: alexander.h.duyck@linux.intel.com Cc: "Michal Hocko" <mhocko@kernel.org>, "Linux MM" <linux-mm@kvack.org>, "Andrew Morton" <akpm@linux-foundation.org>, "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, linux-nvdimm <linux-nvdimm@lists.01.org>, "Pasha Tatashin" <pavel.tatashin@microsoft.com>, "Dave Jiang" <dave.jiang@intel.com>, "Dave Hansen" <dave.hansen@intel.com>, "Jérôme Glisse" <jglisse@redhat.com>, rppt@linux.vnet.ibm.com, "Logan Gunthorpe" <logang@deltatee.com>, "Ingo Molnar" <mingo@kernel.org>, "Kirill A. Shutemov" <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: Wed, 26 Sep 2018 11:52:56 -0700 [thread overview] Message-ID: <CAPcyv4iVnodai0bB74yeSCD2H+hoLsZYUk4sR9jV0pPAE+Zorw@mail.gmail.com> (raw) In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> On Wed, Sep 26, 2018 at 11:25 AM Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote: > > > > On 9/26/2018 12:55 AM, Michal Hocko wrote: > > On Tue 25-09-18 13:21:24, Alexander Duyck wrote: > >> The ZONE_DEVICE pages were being initialized in two locations. One was with > >> the memory_hotplug lock held and another was outside of that lock. The > >> problem with this is that it was nearly doubling the memory initialization > >> time. Instead of doing this twice, once while holding a global lock and > >> once without, I am opting to defer the initialization to the one outside of > >> the lock. This allows us to avoid serializing the overhead for memory init > >> and we can instead focus on per-node init times. > >> > >> One issue I encountered is that devm_memremap_pages and > >> hmm_devmmem_pages_create were initializing only the pgmap field the same > >> way. One wasn't initializing hmm_data, and the other was initializing it to > >> a poison value. Since this is something that is exposed to the driver in > >> the case of hmm I am opting for a third option and just initializing > >> hmm_data to 0 since this is going to be exposed to unknown third party > >> drivers. > > > > Why cannot you pull move_pfn_range_to_zone out of the hotplug lock? In > > other words why are you making zone device even more special in the > > generic hotplug code when it already has its own means to initialize the > > pfn range by calling move_pfn_range_to_zone. Not to mention the code > > duplication. > > So there were a few things I wasn't sure we could pull outside of the > hotplug lock. One specific example is the bits related to resizing the > pgdat and zone. I wanted to avoid pulling those bits outside of the > hotplug lock. > > The other bit that I left inside the hot-plug lock with this approach > was the initialization of the pages that contain the vmemmap. > > > That being said I really dislike this patch. > > In my mind this was a patch that "killed two birds with one stone". I > had two issues to address, the first one being the fact that we were > performing the memmap_init_zone while holding the hotplug lock, and the > other being the loop that was going through and initializing pgmap in > the hmm and memremap calls essentially added another 20 seconds > (measured for 3TB of memory per node) to the init time. With this patch > I was able to cut my init time per node by that 20 seconds, and then > made it so that we could scale as we added nodes as they could run in > parallel. Yeah, at the very least there is no reason for devm_memremap_pages() to do another loop through all pages, the core should handle this, but cleaning up the scope of the hotplug lock is needed. > With that said I am open to suggestions if you still feel like I need to > follow this up with some additional work. I just want to avoid > introducing any regressions in regards to functionality or performance. Could we push the hotplug lock deeper to the places that actually need it? What I found with my initial investigation is that we don't even need the hotplug lock for the vmemmap initialization with this patch [1]. Alternatively it seems the hotplug lock wants to synchronize changes to the zone and the page init work. If the hotplug lock was an rwsem the zone changes would be a write lock, but the init work could be done as a read lock to allow parallelism. I.e. still provide a sync point to be able to assert that no hotplug work is in-flight will holding the write lock, but otherwise allow threads that are touching independent parts of the memmap to run at the same time. [1]: https://patchwork.kernel.org/patch/10527229/ just focus on the mm/sparse-vmemmap.c changes at the end.
next prev parent reply other threads:[~2018-09-26 18:53 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 [this message] 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 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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