Re: [LSF/MM/BPF TOPIC] Swap Abstraction / Native Zswap

[Yosry Ahmed <yosryahmed@google.com>]

On Thu, Mar 9, 2023 at 6:08 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> On Sat, Feb 18, 2023 at 02:38:40PM -0800, Yosry Ahmed wrote:
> > ==================== Intro ====================
> > Currently, using zswap is dependent on swapfiles in an unnecessary
> > way. To use zswap, you need a swapfile configured (even if the space
> > will not be used) and zswap is restricted by its size.
>
> There's also overlap with zram too. zswap uses zpool and so does its
> compression backends (zbud, zsmalloc, z3fold), but zram does not. Vitaly
> did a great job at presenting some overlap between all this before, so
> perhaps we can summon him as I'd imagine he'd be interested.
>
> https://lpc.events/event/4/contributions/551/attachments/364/597/zram-decouple.pdf

Yes. Hopefully by making zswap independent from swapfiles we partially
bridge the gap between zswap and zram.

>
> FWIW we've been using zswap with the whole intention of *never* touching
> disk on purpose for years now on kdevops with the goal to just do compression
> of memory and avoid having to mess with a block device as preamble. This is
> done on the hypervisor with tons of guests, that together with KSM saves *huge*
> amount of memory:
>
> https://github.com/linux-kdevops/kdevops/blob/master/docs/kernel-ci/kernel-ci-hypervisor-tuning.md

At Google, we have been also using zswap without writeback for years.
It's great to hear that others share the same use case. Perhaps it's
finally time to properly support this use case upstream.

>
>   Luis