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From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
To: Michal Hocko <mhocko@kernel.org>
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>,
	"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: Wed, 10 Oct 2018 10:39:01 -0700	[thread overview]
Message-ID: <98c35e19-13b9-0913-87d9-b3f1ab738b61@linux.intel.com> (raw)
In-Reply-To: <20181010172451.GK5873@dhcp22.suse.cz>



On 10/10/2018 10:24 AM, Michal Hocko wrote:
> On Wed 10-10-18 09:39:08, Alexander Duyck wrote:
>> On 10/10/2018 2:58 AM, Michal Hocko wrote:
>>> On Tue 09-10-18 13:26:41, Alexander Duyck wrote:
>>> [...]
>>>> I would think with that being the case we still probably need the call to
>>>> __SetPageReserved to set the bit with the expectation that it will not be
>>>> cleared for device-pages since the pages are not onlined. Removing the call
>>>> to __SetPageReserved would probably introduce a number of regressions as
>>>> there are multiple spots that use the reserved bit to determine if a page
>>>> can be swapped out to disk, mapped as system memory, or migrated.
>>>
>>> PageReserved is meant to tell any potential pfn walkers that might get
>>> to this struct page to back off and not touch it. Even though
>>> ZONE_DEVICE doesn't online pages in traditional sense it makes those
>>> pages available for further use so the page reserved bit should be
>>> cleared.
>>
>> So from what I can tell that isn't necessarily the case. Specifically if the
>> pagemap type is MEMORY_DEVICE_PRIVATE or MEMORY_DEVICE_PUBLIC both are
>> special cases where the memory may not be accessible to the CPU or cannot be
>> pinned in order to allow for eviction.
> 
> Could you give me an example please?

Honestly I am getting a bit beyond my depth here so maybe Dan could 
explain better. I am basing the above comment on Dan's earlier comment 
in this thread combined with the comment that explains the "memory_type" 
field for the pgmap:
https://elixir.bootlin.com/linux/v4.19-rc7/source/include/linux/memremap.h#L28

>> The specific case that Dan and Yi are referring to is for the type
>> MEMORY_DEVICE_FS_DAX. For that type I could probably look at not setting the
>> reserved bit. Part of me wants to say that we should wait and clear the bit
>> later, but that would end up just adding time back to initialization. At
>> this point I would consider the change more of a follow-up optimization
>> rather than a fix though since this is tailoring things specifically for DAX
>> versus the other ZONE_DEVICE types.
> 
> I thought I have already made it clear that these zone device hacks are
> not acceptable to the generic hotplug code. If the current reserve bit
> handling is not correct then give us a specific reason for that and we
> can start thinking about the proper fix.

I might have misunderstood your earlier comment then. I thought you were 
saying that we shouldn't bother with setting the reserved bit. Now it 
sounds like you were thinking more along the lines of what I was here in 
my comment where I thought the bit should be cleared later in some code 
specifically related to DAX when it is exposing it for use to userspace 
or KVM.
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  reply	other threads:[~2018-10-10 17:39 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 [this message]
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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