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Date: Wed, 3 Jan 2024 10:19:06 -0500
From: Dan Schatzberg <schatzberg.dan@gmail.com>
To: Yu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Yosry Ahmed <yosryahmed@google.com>, Huan Yang <link@vivo.com>,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>,
	Jonathan Corbet <corbet@lwn.net>, Michal Hocko <mhocko@kernel.org>,
	Shakeel Butt <shakeelb@google.com>,
	Muchun Song <muchun.song@linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	SeongJae Park <sj@kernel.org>,
	"Vishal Moola (Oracle)" <vishal.moola@gmail.com>,
	Nhat Pham <nphamcs@gmail.com>, Yue Zhao <findns94@gmail.com>
Subject: Re: [PATCH v5 2/2] mm: add swapiness= arg to memory.reclaim
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On Tue, Jan 02, 2024 at 05:27:18PM -0700, Yu Zhao wrote:
[...]
> > Helper aside, I disagree with this point about coupling with the
> > proactive flag.
> 
> Sure. But I would like to hear a *concrete* counterexample.
> 
> > The fact that the only user currently is proactive
> > reclaim
> 
> Yes, that's a fact, and we should make the decision based on the
> current known facts.
> 
> > doesn't imply to me that the interface (in scan_control)
> > should be coupled to the use-case.
> 
> Future always has its uncertainty which I would not worry so much about.
> 
> > It's easier to reason about a
> > swappiness field that overrides swappiness for all scans that set it
> > regardless of the users.
> 
> For example? And how likely would that happen in the next few years?

My argument isn't that making the interface more generic will be
worthwhile due to some future use-case. Rather my argument is that
making the interface more generic makes the code simpler. All else
being equal, having sc->swappiness behave the same regardless of
sc->proactive makes vmscan.c and struct scan_control easier to follow.

That being said - I'm fine with conceding this point - particularly
since both you and Michal appear to feel similarly. I'll make the
corresponding change and send out a new version.