linux-kernel - Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

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Message-ID: <CA+PVUaRnd0vjTNQqdFG-pLYVqaquP46+YOOYWtMpJkNtkF+S6Q@mail.gmail.com>
Date: Fri, 15 Dec 2023 10:50:16 +0100
From: Fabian Deutsch <fdeutsch@...hat.com>
To: Chris Li <chrisl@...nel.org>
Cc: Yu Zhao <yuzhao@...gle.com>, Johannes Weiner <hannes@...xchg.org>, 
	Minchan Kim <minchan@...nel.org>, Nhat Pham <nphamcs@...il.com>, 
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "tj@...nel.org" <tj@...nel.org>, 
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	Kairui Song <kasong@...cent.com>, Zhongkun He <hezhongkun.hzk@...edance.com>
Subject: Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

On Fri, Dec 15, 2023 at 10:40 AM Chris Li <chrisl@...nel.org> wrote:
>
> On Thu, Dec 14, 2023 at 11:42 PM Fabian Deutsch <fdeutsch@...hat.com> wrote:.
> > >
> > > Just to clarify, the "node" you mean the "node" in kubernetes sense,
> > > which is the whole machine. In the Linux kernel MM context, the node
> > > often refers to the NUMA memory node, that is not what you mean here,
> > > right?
> >
> > Correct, I was referring to a kubernetes node, not numa node.
> >
> > >
> > >> - With todays node level swap, and setting memory.swap.max=0 for all cgroups allows you toachieve a similar behavior (only opt-in cgroups will get swap).
> > >> - the above approach however will still have a shared swap backend for all cgroups.
> > >
> > > Yes, the "memory.swap.tires" idea is trying to allow cgroups to select
> > > a subset of the swap backend in a specific order. It is still in the
> > > early stage of discussion. If you have any suggestion or feedback in
> > > that direction, I am looking forward to hearing that.
> >
> > Interesting. There have been concerns to leak confidential data accidentally when it's getting written to a swap device.
>
> One common solution is to encrypt the data written to the device. If
> someone gets hold of the swapped outed device without the key, they
> can't get to the memory data without the key.


Yes - I guess like writing it onto a dmcrypt device with some random key.
Nevertheless, this was one of the topics.

>
>
> > The other less discussed item was QoS for swap io traffic.
> >
> > At a first glance it seems like tires could help with the second use-case.
>
> The idea is that you can select the swap tiers list for each cgroup.
> That way  you can assign different swap QoS to different cgroup.


Yes, it sounds like a fit.
What use-cases did you have in mind for the tiers feature?