From: Michal Hocko <mhocko@kernel.org>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
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, akpm@linux-foundation.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: Thu, 27 Sep 2018 13:09:26 +0200 [thread overview]
Message-ID: <20180927110926.GE6278@dhcp22.suse.cz> (raw)
In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com>
On Wed 26-09-18 11:25:37, Alexander Duyck 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.
Why would that be a problem. There are dedicated locks for resizing.
> The other bit that I left inside the hot-plug lock with this approach was
> the initialization of the pages that contain the vmemmap.
Again, why this is needed?
> > 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.
>
> 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.
Yes, I really do prefer this to be done properly rather than tweak it
around because of uncertainties.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2018-09-27 11:09 UTC|newest]
Thread overview: 77+ 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 20:19 ` [PATCH v5 1/4] mm: Remove now defunct NO_BOOTMEM from depends list for deferred init Alexander Duyck
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 20:26 ` Dave Hansen
2018-09-25 20:38 ` Alexander Duyck
2018-09-25 22:14 ` Dave Hansen
2018-09-25 22:27 ` Alexander Duyck
2018-09-26 7:38 ` Michal Hocko
2018-09-26 15:24 ` Alexander Duyck
2018-09-26 15:39 ` Michal Hocko
2018-09-26 15:41 ` Dave Hansen
2018-09-26 16:18 ` Alexander Duyck
2018-09-26 15:36 ` Dave Hansen
2018-09-26 22:36 ` Andrew Morton
2018-09-25 20:20 ` [PATCH v5 3/4] mm: Create non-atomic version of SetPageReserved for init use 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
2018-09-26 7:55 ` Michal Hocko
2018-09-26 18:25 ` Alexander Duyck
2018-09-26 18:52 ` Dan Williams
2018-09-27 11:20 ` Michal Hocko
2018-09-27 11:09 ` Michal Hocko [this message]
2018-09-27 12:25 ` Oscar Salvador
2018-09-27 13:13 ` Michal Hocko
2018-09-27 14:50 ` Oscar Salvador
2018-09-27 15:41 ` David Hildenbrand
2018-09-28 8:12 ` Oscar Salvador
2018-09-28 8:44 ` Oscar Salvador
2018-09-28 15:50 ` Dan Williams
2018-09-27 12:32 ` Oscar Salvador
2018-10-08 21:01 ` Dan Williams
2018-10-08 21:38 ` Alexander Duyck
2018-10-08 22:00 ` Dan Williams
2018-10-08 22:07 ` 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
2018-10-09 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 18:04 ` Dan Williams
2018-10-09 20:26 ` Alexander Duyck
2018-10-09 21:19 ` Dan Williams
2018-10-10 12:52 ` Yi Zhang
2018-10-10 15:27 ` Alexander Duyck
2018-10-11 8:17 ` Yi Zhang
2018-10-10 9:58 ` Michal Hocko
2018-10-10 16:39 ` Alexander Duyck
2018-10-10 17:24 ` Michal Hocko
2018-10-10 17:39 ` Alexander Duyck
2018-10-10 17:53 ` Michal Hocko
2018-10-10 18:13 ` Alexander Duyck
2018-10-10 18:52 ` Michal Hocko
2018-10-11 8:55 ` Michal Hocko
2018-10-11 17:38 ` Alexander Duyck
2018-10-11 18:22 ` Dan Williams
2018-10-17 7:52 ` Michal Hocko
2018-10-17 15:02 ` Alexander Duyck
2018-10-29 14:12 ` Michal Hocko
2018-10-29 15:59 ` Alexander Duyck
2018-10-29 16:35 ` Michal Hocko
2018-10-29 17:01 ` Alexander Duyck
2018-10-29 17:24 ` Michal Hocko
2018-10-29 17:34 ` Dan Williams
2018-10-29 17:45 ` Michal Hocko
2018-10-29 17:42 ` Alexander Duyck
2018-10-29 18:18 ` Michal Hocko
2018-10-29 19:59 ` Alexander Duyck
2018-10-30 6:29 ` Michal Hocko
2018-10-30 6:55 ` Dan Williams
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 15:56 ` Michal Hocko
2018-10-10 18:18 ` Dan Williams
2018-10-11 8:39 ` Yi Zhang
2018-10-11 15:38 ` Alexander Duyck
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