linux-kernel - Re: [PATCH 0/1] Add swappiness argument to memory.reclaim

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Message-ID: <CALvZod7Buc1TPXFDA2fE8+apE9VJDA=uAYB1u00kyZy9oLbmgA@mail.gmail.com>
Date:   Thu, 30 Nov 2023 13:52:26 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dan Schatzberg <schatzberg.dan@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Yosry Ahmed <yosryahmed@...gle.com>, Huan Yang <link@...o.com>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Peter Xu <peterx@...hat.com>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        Yue Zhao <findns94@...il.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 0/1] Add swappiness argument to memory.reclaim

On Thu, Nov 30, 2023 at 1:37 PM Dan Schatzberg <schatzberg.dan@...il.com> wrote:
>
> On Thu, Nov 30, 2023 at 12:30:27PM -0800, Shakeel Butt wrote:
> > On Thu, Nov 30, 2023 at 11:47 AM Dan Schatzberg
> > <schatzberg.dan@...il.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?
>
> I can't think of any reason why we would want swappiness interpreted
> differently if it's provided at proactive reclaim time vs
> globally. Did you have something in mind here?

Nah just wanted to know what you are aiming for.