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/
prev parent 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 \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).