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From:   Shakeel Butt <shakeelb@google.com>
Date:   Thu, 30 Nov 2023 12:30:27 -0800
Message-ID: <CALvZod5dkpnF5h3u3cfdD4L8SExPZCXaPpt4fvpeVRiHPS8ySA@mail.gmail.com>
Subject: Re: [PATCH 0/1] Add swappiness argument to memory.reclaim
To:     Dan Schatzberg <schatzberg.dan@gmail.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        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, Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Huang Ying <ying.huang@intel.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Peter Xu <peterx@redhat.com>,
        "Vishal Moola (Oracle)" <vishal.moola@gmail.com>,
        Yue Zhao <findns94@gmail.com>, Hugh Dickins <hughd@google.com>
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On Thu, Nov 30, 2023 at 11:47=E2=80=AFAM Dan Schatzberg
<schatzberg.dan@gmail.com> wrote:
>
> On Thu, Nov 30, 2023 at 11:56:42AM -0500, Johannes Weiner wrote:
> > [...]
> > So I wouldn't say it's merely a reclaim hint. It controls a very
> > concrete and influential factor in VM decision making. And since the
> > global swappiness is long-established ABI, I don't expect its meaning
> > to change significantly any time soon.
>
> I want to add to this last point. While swappiness does not have
> terribly well-defined semantics - it is the (only?) existing mechanism
> to control balance between anon and file reclaim. I'm merely
> advocating for the ability to adjust swappiness during proactive
> reclaim separately from reactive reclaim. To what degree the behavior
> and semantics of swappiness change is a bit orthogonal here.

Let me ask my question in this chain as it might have been missed:

Whatever the semantics of swappiness are (including the edge cases
like no swap, file_is_tiny, trim cache), should the reclaim code treat
the global swappiness and user-provided swappiness differently?