Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store().

[Johannes Weiner]

On Thu, Sep 26, 2024 at 05:29:30PM +0000, Sridhar, Kanchana P wrote:
> > > 3) Keep the approach in v7 where obj_cgroup_get/put is localized to
> > >     zswap_store_page for both success and error conditions, and any
> > unwinding
> > >     state in zswap_store will take care of dropping references obtained from
> > >     prior successful writes (from this or prior invocations of zswap_store).
> > 
> > I am also fine with doing that and doing the reference batching as a follow up.
> 
> I think so too! We could try and improve upon (3) with reference batching
> in a follow-up patch.

Yeah, I agree. The percpu-refcounts are not that expensive, we should
be able to live with per-page ops for now.

One thing you *can* do from the start is tryget a pool reference in
zswap_store(), to prevent the pools untimely demise while you work on
it, and then in zswap_store_page() you can do gets instead of trygets.

You'd have to rename zswap_pool_get() to zswap_pool_tryget() (which is
probably for the best) and implement the trivial new zswap_pool_get().