nvdimm.lists.linux.dev archive mirror
 help / color / mirror / Atom feed
From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
To: "Dan Williams" <dan.j.williams@intel.com>,
	"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 Hansen" <dave.hansen@intel.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	rppt@linux.vnet.ibm.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: Thu, 11 Oct 2018 08:38:56 -0700	[thread overview]
Message-ID: <ded6694d-a283-2954-c61a-001800c000df@linux.intel.com> (raw)
In-Reply-To: <20181011083953.GB51021@tiger-server>

On 10/11/2018 1:39 AM, Yi Zhang wrote:
> On 2018-10-10 at 11:18:49 -0700, Dan Williams wrote:
>> On Wed, Oct 10, 2018 at 10:30 AM Michal Hocko <mhocko@kernel.org> 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?
>>>
>>>> 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.
>>>
>>
>> Right, so we're in a situation where a hack is needed for KVM's
>> current interpretation of the Reserved flag relative to dax mapped
>> pages. I'm arguing to push that knowledge / handling as deep as
>> possible into the core rather than hack the leaf implementations like
>> KVM, i.e. disable the Reserved flag for all non-MEMORY_DEVICE_*
>> ZONE_DEVICE types.
>>
>> Here is the KVM thread about why they need a change:
>>
>>      https://lkml.org/lkml/2018/9/7/552
>>
>> ...and where I pushed back on a KVM-local hack:
>>
>>      https://lkml.org/lkml/2018/9/19/154
> Yeah, Thank Dan, I think I can going on with something like this:
> 
> @@ -5589,6 +5589,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
>   		struct page *page = pfn_to_page(pfn);
>   
>   		__init_single_page(page, pfn, zone_idx, nid);
> +		/* Could we move this a little bit earlier as I can
> +		 * direct use is_dax_page(page), or something else?
> +		 */
> +		page->pgmap = pgmap;
>   
>   		/*
>   		 * Mark page reserved as it will need to wait for onlining
> @@ -5597,14 +5598,14 @@ void __ref memmap_init_zone_device(struct zone *zone,
>   		 * We can use the non-atomic __set_bit operation for setting
>   		 * the flag as we are still initializing the pages.
>   		 */
> -		__SetPageReserved(page);
> +		 if(!is_dax_page(page))
> +			__SetPageReserved(page);
>   
>   		/*
>   		 * ZONE_DEVICE pages union ->lru with a ->pgmap back
>   		 * pointer and hmm_data.  It is a bug if a ZONE_DEVICE
>   		 * page is ever freed or placed on a driver-private list.
>   		 */
> -		page->pgmap = pgmap;
>   		page->hmm_data = 0;
> 
> 
> After Alex's patch merged.

So I am not a huge fan of splitting up the pgmap init from the hmm_data, 
but I suppose this is just for your proof-of-concept?

I already have another patch set outstanding that may actually make this 
change easier[1]. What I could do is add the logic there based on the 
pgmap.type as an additional patch since I pass a boolean to determine if 
I am setting the reserved bit or not.

[1] 
https://lore.kernel.org/lkml/20181005151006.17473.83040.stgit@localhost.localdomain/

_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

      reply	other threads:[~2018-10-11 15:39 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
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 [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ded6694d-a283-2954-c61a-001800c000df@linux.intel.com \
    --to=alexander.h.duyck@linux.intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@intel.com \
    --cc=jglisse@redhat.com \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=mhocko@kernel.org \
    --cc=mingo@kernel.org \
    --cc=pavel.tatashin@microsoft.com \
    --cc=rppt@linux.vnet.ibm.com \
    --subject='Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox