Re: [PATCH v3 4/4] mm: zswap: remove same_filled module params

[Yosry Ahmed]

On Sat, Apr 13, 2024 at 10:56:47PM +0200, Maciej S. Szmigiero wrote:
> On 13.04.2024 04:24, Yosry Ahmed wrote:
> > These knobs offer more fine-grained control to userspace than needed and
> > directly expose/influence kernel implementation; remove them.
> > 
> > For disabling same_filled handling, there is no logical reason to refuse
> > storing same-filled pages more efficiently and opt for compression.
> > Scanning pages for patterns may be an argument, but the page contents
> > will be read into the CPU cache anyway during compression. Also,
> > removing the same_filled handling code does not move the needle
> > significantly in terms of performance anyway [1].
> > 
> > For disabling non_same_filled handling, it was added when the compressed
> > pages in zswap were not being properly charged to memcgs, as workloads
> > could escape the accounting with compression [2]. This is no longer the
> > case after commit f4840ccfca25 ("zswap: memcg accounting"), and using
> > zswap without compression does not make much sense.
> > 
> > [1]https://lore.kernel.org/lkml/CAJD7tkaySFP2hBQw4pnZHJJwe3bMdjJ1t9VC2VJd=khn1_TXvA@xxxxxxxxxxxxxx/
> > [2]https://lore.kernel.org/lkml/19d5cdee-2868-41bd-83d5-6da75d72e940@xxxxxxxxxxxxxxxxxxxxx/
> > 
> > Cc: "Maciej S. Szmigiero" <mail@xxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
> > Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
> > ---
> 
> I think you need to update zswap kernel docs, too.

Ah yes, I had local changes to update the docs but apparently never
committed them. Thanks for catching this.

Andrew, could you please fold in the following patch or merge it as as
separate one? Whatever you prefer. Thanks.