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From: Michal Hocko <mhocko@kernel.org>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: "Pasha Tatashin" <pavel.tatashin@microsoft.com>,
	osalvador@techadventures.net,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	"Dave Hansen" <dave.hansen@intel.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Ingo Molnar" <mingo@kernel.org>, "Linux MM" <linux-mm@kvack.org>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	rppt@linux.vnet.ibm.com,
	"Andrew Morton" <akpm@linux-foundation.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: Tue, 30 Oct 2018 07:29:15 +0100	[thread overview]
Message-ID: <20181030062915.GT32673@dhcp22.suse.cz> (raw)
In-Reply-To: <3281f3044fa231bbc1b02d5c5efca3502a0d05a8.camel@linux.intel.com>

On Mon 29-10-18 12:59:11, Alexander Duyck wrote:
> On Mon, 2018-10-29 at 19:18 +0100, Michal Hocko wrote:
[...]

I will try to get to your other points later.

> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 89d2a2ab3fe6..048e4cc72fdf 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5474,8 +5474,8 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >  	 * Honor reservation requested by the driver for this ZONE_DEVICE
> >  	 * memory
> >  	 */
> > -	if (altmap && start_pfn == altmap->base_pfn)
> > -		start_pfn += altmap->reserve;
> > +	if (pgmap && pgmap->get_memmap)
> > +		start_pfn = pgmap->get_memmap(pgmap, start_pfn);
> >  
> >  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> >  		/*
> > 
> > [...]
> 
> The only reason why I hadn't bothered with these bits is that I was
> actually trying to leave this generic since I thought I had seen other
> discussions about hotplug scenerios where memory may want to change
> where the vmmemmap is initialized other than just the case of
> ZONE_DEVICE pages. So I was thinking at some point we may see altmap
> without the pgmap.

I wanted to abuse altmap to allocate struct pages from the physical
range to be added. In that case I would abstract the
allocation/initialization part of pgmap into a more abstract type.
Something trivially to be done without affecting end users of the
hotplug API.

[...]
> > Anyway we have gone into details while the primary problem here was that
> > the hotplug lock doesn't scale AFAIR. And my question was why cannot we
> > pull move_pfn_range_to_zone and what has to be done to achieve that.
> > That is a fundamental thing to address first. Then you can microptimize
> > on top.
> 
> Yes, the hotplug lock was part of the original issue. However that
> starts to drift into the area I believe Oscar was working on as a part
> of his patch set in encapsulating the move_pfn_range_to_zone and other
> calls that were contained in the hotplug lock into their own functions.

Well, I would really love to keep the external API as simple as
possible. That means that we need arch_add_memory/add_pages and 
move_pfn_range_to_zone to associate pages with a zone. The hotplug lock
should be preferably hidden from callers of those two and ideally it
shouldn't be a global lock. We should be good with a range lock.
 
> The patches Andrew pushed addressed the immediate issue so that now
> systems with nvdimm/DAX memory can at least initialize quick enough
> that systemd doesn't refuse to mount the root file system due to a
> timeout.

This is about the first time you actually mention that. I have re-read
the cover letter and all changelogs of patches in this serious. Unless I
have missed something there is nothing about real users hitting issues
out there. nvdimm is still considered a toy because there is no real HW
users can play with.

And hence my complains about half baked solutions rushed in just to fix
a performance regression. I can certainly understand that a pressing
problem might justify to rush things a bit but this should be always
carefuly justified.

> The next patch set I have refactors things to reduce code and
> allow us to reuse some of the hotplug code for the deferred page init, 
> https://lore.kernel.org/lkml/20181017235043.17213.92459.stgit@localhost.localdomain/
> . After that I was planning to work on dealing with the PageReserved
> flag and trying to get that sorted out.
> 
> I was hoping to wait until after Dan's HMM patches and Oscar's changes
> had been sorted before I get into any further refactor of this specific
> code.

Yes there is quite a lot going on here. I would really appreciate if we
all sit and actually try to come up with something robust rather than
hack here and there. I haven't yet seen your follow up series completely
so maybe you are indeed heading the correct direction.

-- 
Michal Hocko
SUSE Labs
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Linux-nvdimm@lists.01.org
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  reply	other threads:[~2018-10-30  6:29 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
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 [this message]
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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