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From: Dave Hansen <dave.hansen@intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
	mgorman@techsingularity.net, riel@surriel.com,
	hannes@cmpxchg.org, akpm@linux-foundation.org,
	keith.busch@intel.com, dan.j.williams@intel.com,
	fengguang.wu@intel.com, fan.du@intel.com, ying.huang@intel.com,
	ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node
Date: Wed, 17 Apr 2019 10:13:44 -0700
Message-ID: <5c2d37e1-c7f6-5b7b-4f8e-a34e981b841e@intel.com> (raw)
In-Reply-To: <20190417092318.GG655@dhcp22.suse.cz>

On 4/17/19 2:23 AM, Michal Hocko wrote:
>> 3. The demotion path can not have cycles
> yes. This could be achieved by GFP_NOWAIT opportunistic allocation for
> the migration target. That should prevent from loops or artificial nodes
> exhausting quite naturaly AFAICS. Maybe we will need some tricks to
> raise the watermark but I am not convinced something like that is really
> necessary.

I don't think GFP_NOWAIT alone is good enough.

Let's say we have a system full of clean page cache and only two nodes:
0 and 1.  GFP_NOWAIT will eventually kick off kswapd on both nodes.
Each kswapd will be migrating pages to the *other* node since each is in
the other's fallback path.

I think what you're saying is that, eventually, the kswapds will see
allocation failures and stop migrating, providing hysteresis.  This is
probably true.

But, I'm more concerned about that window where the kswapds are throwing
pages at each other because they're effectively just wasting resources
in this window.  I guess we should figure our how large this window is
and how fast (or if) the dampening occurs in practice.

  parent reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-11  3:56 Yang Shi
2019-04-11  3:56 ` [v2 PATCH 1/9] mm: define N_CPU_MEM node states Yang Shi
2019-04-11  3:56 ` [v2 PATCH 2/9] mm: page_alloc: make find_next_best_node find return cpuless node Yang Shi
2019-04-11  3:56 ` [v2 PATCH 3/9] mm: numa: promote pages to DRAM when it gets accessed twice Yang Shi
2019-04-11  3:56 ` [v2 PATCH 4/9] mm: migrate: make migrate_pages() return nr_succeeded Yang Shi
2019-04-11  3:56 ` [v2 PATCH 5/9] mm: vmscan: demote anon DRAM pages to PMEM node Yang Shi
2019-04-11 14:31   ` Dave Hansen
2019-04-15 22:10     ` Yang Shi
2019-04-15 22:14       ` Dave Hansen
2019-04-15 22:26         ` Yang Shi
2019-04-11  3:56 ` [v2 PATCH 6/9] mm: vmscan: don't demote for memcg reclaim Yang Shi
2019-04-11  3:56 ` [v2 PATCH 7/9] mm: vmscan: check if the demote target node is contended or not Yang Shi
2019-04-11 16:06   ` Dave Hansen
2019-04-15 22:06     ` Yang Shi
2019-04-15 22:13       ` Dave Hansen
2019-04-15 22:23         ` Yang Shi
2019-04-11  3:56 ` [v2 PATCH 8/9] mm: vmscan: add page demotion counter Yang Shi
2019-04-11  3:56 ` [v2 PATCH 9/9] mm: numa: add page promotion counter Yang Shi
2019-04-11 14:28 ` [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node Dave Hansen
2019-04-12  8:47 ` Michal Hocko
2019-04-16  0:09   ` Yang Shi
2019-04-16  7:47     ` Michal Hocko
2019-04-16 14:30       ` Dave Hansen
2019-04-16 14:39         ` Michal Hocko
2019-04-16 15:46           ` Dave Hansen
2019-04-16 18:34             ` Michal Hocko
2019-04-16 15:33         ` Zi Yan
2019-04-16 15:55           ` Dave Hansen
2019-04-16 16:12             ` Zi Yan
2019-04-16 19:19       ` Yang Shi
2019-04-16 21:22         ` Dave Hansen
2019-04-16 21:59           ` Yang Shi
2019-04-16 23:04             ` Dave Hansen
2019-04-16 23:17               ` Yang Shi
2019-04-17 15:13                 ` Keith Busch
2019-04-17  9:23           ` Michal Hocko
2019-04-17 15:23             ` Keith Busch
2019-04-17 15:39               ` Michal Hocko
2019-04-17 15:37                 ` Keith Busch
2019-04-17 16:39                   ` Michal Hocko
2019-04-17 17:26                     ` Yang Shi
2019-04-17 17:29                       ` Keith Busch
2019-04-17 17:51                       ` Michal Hocko
2019-04-18 16:24                         ` Yang Shi
2019-04-17 17:13             ` Dave Hansen [this message]
2019-04-17 17:57               ` Michal Hocko
2019-04-18 18:16               ` Keith Busch
2019-04-18 19:23                 ` Yang Shi
2019-04-18 21:07                   ` Zi Yan
2019-04-16 23:18         ` Yang Shi
2019-04-17  9:17         ` Michal Hocko
2019-05-01  6:43           ` Fengguang Wu
2019-04-17 20:43         ` Yang Shi
2019-04-18  9:02           ` Michal Hocko
2019-05-01  5:20             ` Fengguang Wu

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