Re: [PATCH v3 1/4] mm/zswap: Make shrink_worker writeback cursor per-memcg

[Shakeel Butt]

On Thu, Jun 11, 2026 at 05:39:16PM +0000, Yosry Ahmed wrote:
> On Tue, Jun 09, 2026 at 11:18:26AM +0800, Hao Jia wrote:
> > 
> > 
> > On 2026/6/9 02:01, Nhat Pham wrote:
> > > On Mon, Jun 8, 2026 at 9:48 AM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> > > > 
> > > > > But OTOH, this does seem like a recipe for inefficient reclaim. We
> > > > > might exhaust hotter memory of a cgroup while sparing colder memory of
> > > > > another cgroup... But maybe if they're all cold anyway, then who
> > > > > cares, and eventually you'll get to the cold stuff of other child?
> > > > 
> > > > Forgot to respond to this part, the unfairness is limited to the batch
> > > > size per-invocation, so it should be fine as long as you don't divide
> > > > the amount over 100 iterations for some reason. Also yes, all memory
> > > > in zswap is cold, the relative coldness is not that important (e.g.
> > > > compared to relative coldness during reclaim).
> > > 
> > > Ok then yeah, I think we should shelve per-memcg cursor for the next
> > > version. Down the line, if we have more data that unfairness is an
> > > issue, we can always fix it. One step at a time :)
> > 
> > Thanks a lot to Yosry, Nhat, and Shakeel for the great suggestions!
> > 
> > Let me summarize what I plan to do in the next version to make sure we are
> > on the same page:
> > 
> >  - Drop the per-memcg cursor and keep the root cgroup cursor
> > (zswap_next_shrink) logic intact.
> >  - Stick to using the zswap_writeback_only key, and change the proactive
> > writeback size to use the compressed size.
> >  - Consolidate and reuse the logic between shrink_worker() and
> > shrink_memcg(). Enable batch writeback in the shrink_worker() path, while
> > keeping the writeback behavior in the zswap_store() path unchanged.
> > 
> > Please let me know if I missed or misunderstood anything. Thanks again for
> > clearing things up!
> 
> Sorry for the late response, yes I think this makes sense. However, I
> have some comment about how this interacts with swap tiering, let me
> reply to the other thread.
> 

I think the swap tiers interaction will be figured out over next cycle. However
Hao can/should continue to push and we may decide to let it in orthogonal to
swap tiers.