RE: [PATCH v4 0/4] mm: ZSWAP swap-out of mTHP folios

["Sridhar, Kanchana P" <kanchana.p.sridhar@intel.com>]

Hi Yosry,

> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@google.com>
> Sent: Friday, August 23, 2024 8:10 PM
> To: Nhat Pham <nphamcs@gmail.com>
> Cc: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>; linux-
> kernel@vger.kernel.org; linux-mm@kvack.org; hannes@cmpxchg.org;
> ryan.roberts@arm.com; Huang, Ying <ying.huang@intel.com>;
> 21cnbao@gmail.com; akpm@linux-foundation.org; Zou, Nanhai
> <nanhai.zou@intel.com>; Feghali, Wajdi K <wajdi.k.feghali@intel.com>;
> Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v4 0/4] mm: ZSWAP swap-out of mTHP folios
> 
> [..]
> >
> > I'm not trying to delay this patch - I fully believe in supporting
> > zswap for larger pages (both mTHP and THP - whatever the memory
> > reclaim subsystem throws at us).
> >
> > But we need to get to the bottom of this :) These are very suspicious
> > and concerning data. If this is something urgent, I can live with a
> > gate to enable/disable this, but I'd much prefer we understand what's
> > going on here.
> 
> Agreed. I don't think merging this support is urgent, so I think we
> should better understand what is happening here. If there is a problem
> with how we charge compressed memory today (temporary double charges),
> we need to sort this out before the the mTHP support, as it will only
> make things worse.
> 
> I have to admit I didn't take a deep look at the discussion and data,
> so there may be other problems that I didn't notice. It seems to me
> like Kanchana is doing more debugging to understand what is happening,
> so that's great!

This sounds good. I just shared the data and my learnings from some
debugging experiments. I would appreciate it if you can review this and
suggest next steps.

> 
> As for the patches, we should sort out the impact on a higher level
> before discussing implementation details. From a quick look though it
> seems like the first patch can be dropped after Usama's patches that
> remove the same-filled handling from zswap land, and the last two
> patches can be squashed.

Sure, this sounds good.

Thanks,
Kanchana