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From: "Huang\, Ying" <ying.huang@intel.com>
To: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	 <linux-kernel@vger.kernel.org>,  <linux-mm@kvack.org>,
	 <kbusch@kernel.org>,  <yang.shi@linux.alibaba.com>,
	 <dan.j.williams@intel.com>
Subject: Re: [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard
Date: Thu, 02 Jul 2020 13:02:03 +0800
Message-ID: <87mu4ijyr8.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.23.453.2007011203500.1908531@chino.kir.corp.google.com> (David Rientjes's message of "Wed, 1 Jul 2020 12:25:08 -0700")

David Rientjes <rientjes@google.com> writes:

> On Wed, 1 Jul 2020, Dave Hansen wrote:
>
>> > Could this cause us to break a user's mbind() or allow a user to 
>> > circumvent their cpuset.mems?
>> 
>> In its current form, yes.
>> 
>> My current rationale for this is that while it's not as deferential as
>> it can be to the user/kernel ABI contract, it's good *overall* behavior.
>>  The auto-migration only kicks in when the data is about to go away.  So
>> while the user's data might be slower than they like, it is *WAY* faster
>> than they deserve because it should be off on the disk.
>> 
>
> It's outside the scope of this patchset, but eventually there will be a 
> promotion path that I think requires a strict 1:1 relationship between 
> DRAM and PMEM nodes because otherwise mbind(), set_mempolicy(), and 
> cpuset.mems become ineffective for nodes facing memory pressure.

I have posted an patchset for AutoNUMA based promotion support,

https://lore.kernel.org/lkml/20200218082634.1596727-1-ying.huang@intel.com/

Where, the page is promoted upon NUMA hint page fault.  So all memory
policy (mbind(), set_mempolicy(), and cpuset.mems) are available.  We
can refuse promoting the page to the DRAM nodes that are not allowed by
any memory policy.  So, 1:1 relationship isn't necessary for promotion.

> For the purposes of this patchset, agreed that DRAM -> PMEM -> swap makes 
> perfect sense.  Theoretically, I think you could have DRAM N0 and N1 and 
> then a single PMEM N2 and this N2 can be the terminal node for both N0 and 
> N1.  On promotion, I think we need to rely on something stronger than 
> autonuma to decide which DRAM node to promote to: specifically any user 
> policy put into effect (memory tiering or autonuma shouldn't be allowed to 
> subvert these user policies).
>
> As others have mentioned, we lose the allocation or process context at the 
> time of demotion or promotion

As above, we have process context at time of promotion.

> and any workaround for that requires some 
> hacks, such as mapping the page to cpuset (what is the right solution for 
> shared pages?) or adding NUMA locality handling to memcg.

It sounds natural to me to add NUMA nodes restriction to memcg.

Best Regards,
Huang, Ying


  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 23:45 [RFC][PATCH 0/8] Migrate Pages " Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 1/8] mm/numa: node demotion data structure and lookup Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 2/8] mm/migrate: Defer allocating new page until needed Dave Hansen
2020-07-01  8:47   ` Greg Thelen
2020-07-01 14:46     ` Dave Hansen
2020-07-01 18:32       ` Yang Shi
2020-06-29 23:45 ` [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard Dave Hansen
2020-07-01  0:47   ` David Rientjes
2020-07-01  1:29     ` Yang Shi
2020-07-01  5:41       ` David Rientjes
2020-07-01  8:54         ` Huang, Ying
2020-07-01 18:20           ` Dave Hansen
2020-07-01 19:50             ` David Rientjes
2020-07-02  1:50               ` Huang, Ying
2020-07-01 15:15         ` Dave Hansen
2020-07-01 17:21         ` Yang Shi
2020-07-01 19:45           ` David Rientjes
2020-07-02 10:02             ` Jonathan Cameron
2020-07-01  1:40     ` Huang, Ying
2020-07-01 16:48     ` Dave Hansen
2020-07-01 19:25       ` David Rientjes
2020-07-02  5:02         ` Huang, Ying [this message]
2020-06-29 23:45 ` [RFC][PATCH 4/8] mm/vmscan: add page demotion counter Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 5/8] mm/numa: automatically generate node migration order Dave Hansen
2020-06-30  8:22   ` Huang, Ying
2020-07-01 18:23     ` Dave Hansen
2020-07-02  1:20       ` Huang, Ying
2020-06-29 23:45 ` [RFC][PATCH 6/8] mm/vmscan: Consider anonymous pages without swap Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 7/8] mm/vmscan: never demote for memcg reclaim Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 8/8] mm/numa: new reclaim mode to enable reclaim-based migration Dave Hansen
2020-06-30  7:23   ` Huang, Ying
2020-06-30 17:50     ` Yang Shi
2020-07-01  0:48       ` Huang, Ying
2020-07-01  1:12         ` Yang Shi
2020-07-01  1:28           ` Huang, Ying
2020-07-01 16:02       ` Dave Hansen
2020-07-03  9:30   ` Huang, Ying
2020-06-30 18:36 ` [RFC][PATCH 0/8] Migrate Pages in lieu of discard Shakeel Butt
2020-06-30 18:51   ` Dave Hansen
2020-06-30 19:25     ` Shakeel Butt
2020-06-30 19:31       ` Dave Hansen
2020-07-01 14:24         ` [RFC] [PATCH " Zi Yan
2020-07-01 14:32           ` Dave Hansen

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