Re: Path forward for Virtualized Swap?

[Rik van Riel <riel@surriel.com>]

On Mon, 2026-09-21 at 06:11 -1000, Chris Li wrote:
> On Mon, Sep 21, 2026 at 2:53 AM Gregory Price <gourry@gourry.net>
> wrote:
> 
> > 
> > You can't know the compressibility of memory until after you
> > compress
> > it, and requiring a user to predict the future by forcing them to
> > limit
> > the total amount of workload compressibility does not scale with
> > the
> > number of workloads of variable compressibility of data.
> 
> You likely just need to pull a SQL query on your fleet to get that
> number.

This feature is not being developed for just one
user. It has to work for everybody.

> 
> > That should tell you that your model of reasoning about this issue
> > is
> > ill-suited to address the problem.
> 
> That is what I'm suspecting. Nobody in a sane mind would want to
> zswap
> 100% of the RAM and maintain reasonable SLO.
> 
It could make a lot of sense to have some default
limit upstream, that says the zswap pool is not
allowed to take more than half of memory, because
at that point the compressed content will be
crowding other things out of memory.

That seems like the kind of limit that is large
enough that very few people will run into it, 
while also being small enough to prevent actual
corner case trouble.

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