Re: Path forward for Virtualized Swap?

[Nhat Pham]

On Tue, Sep 22, 2026 at 8:23 AM Chris Li <chrisl@xxxxxxxxxx> wrote:
>
> On Tue, Sep 22, 2026 at 4:59 AM Rik van Riel <riel@xxxxxxxxxxx> wrote:
>
> Yes, I can agree on what you observed. You are using anon + zswap on
> that app alone. That is not what I originally asked.
>
> My original request was for the whole system: what percentage of the
> total system RAM size has been swapped out to zswap.
>
> Because when you have 100% of zswap out, it will likely trigger
> different kernel code path on allocating memory. You might suffer
> global memory pressure you did not observe in the single app memory
> pressure case.

What does this 100% figure refer to? Pre- or post- compression size? I
legitimately cannot tell.

"Trigger different kernel code path on allocating memory" what do you
mean by this? This reads like you're referring to post-compression
size, where one cgroup eats up the RAM of the host, affecting other
tenants in that host. But putting a limit on the virtual device
capacity limits the PRE-compression footprint. It is a very
unpredictable way to prevent the effect you're referring to above,
because compression ratio is unpredictable ahead of time.

For post-compression size, I can make arguments on why we should not
also gate it, but regardless we already have zswap.max and the global
zswap pool limit.