linux-kernel - Re: [PATCH v10 6/7] mm: zswap: Support large folios in zswap

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Message-ID: <CAJD7tkYtfHyRgxqb_gGVLfWBHdwzmkD+SRHnBbSdv-59eWLPqA@mail.gmail.com>
Date: Tue, 1 Oct 2024 10:03:48 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Cc: Johannes Weiner <hannes@...xchg.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, 
	"nphamcs@...il.com" <nphamcs@...il.com>, "chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>, 
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "shakeel.butt@...ux.dev" <shakeel.butt@...ux.dev>, 
	"ryan.roberts@....com" <ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>, 
	"21cnbao@...il.com" <21cnbao@...il.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, 
	"willy@...radead.org" <willy@...radead.org>, "Zou, Nanhai" <nanhai.zou@...el.com>, 
	"Feghali, Wajdi K" <wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v10 6/7] mm: zswap: Support large folios in zswap_store().

On Tue, Oct 1, 2024 at 10:01 AM Sridhar, Kanchana P
<kanchana.p.sridhar@...el.com> wrote:
>
> > -----Original Message-----
> > From: Johannes Weiner <hannes@...xchg.org>
> > Sent: Tuesday, October 1, 2024 4:11 AM
> > To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> > Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> > yosryahmed@...gle.com; nphamcs@...il.com;
> > chengming.zhou@...ux.dev; usamaarif642@...il.com;
> > shakeel.butt@...ux.dev; ryan.roberts@....com; Huang, Ying
> > <ying.huang@...el.com>; 21cnbao@...il.com; akpm@...ux-foundation.org;
> > willy@...radead.org; Zou, Nanhai <nanhai.zou@...el.com>; Feghali, Wajdi K
> > <wajdi.k.feghali@...el.com>; Gopal, Vinodh <vinodh.gopal@...el.com>
> > Subject: Re: [PATCH v10 6/7] mm: zswap: Support large folios in
> > zswap_store().
> >
> > On Mon, Sep 30, 2024 at 10:32:21PM -0700, Kanchana P Sridhar wrote:
> > > zswap_store() will store large folios by compressing them page by page.
> > >
> > > This patch provides a sequential implementation of storing a large folio
> > > in zswap_store() by iterating through each page in the folio to compress
> > > and store it in the zswap zpool.
> > >
> > > zswap_store() calls the newly added zswap_store_page() function for each
> > > page in the folio. zswap_store_page() handles compressing and storing each
> > > page.
> > >
> > > We check the global and per-cgroup limits once at the beginning of
> > > zswap_store(), and only check that the limit is not reached yet. This is
> > > racy and inaccurate, but it should be sufficient for now. We also obtain
> > > initial references to the relevant objcg and pool to guarantee that
> > > subsequent references can be acquired by zswap_store_page(). A new
> > function
> > > zswap_pool_get() is added to facilitate this.
> > >
> > > If these one-time checks pass, we compress the pages of the folio, while
> > > maintaining a running count of compressed bytes for all the folio's pages.
> > > If all pages are successfully compressed and stored, we do the cgroup
> > > zswap charging with the total compressed bytes, and batch update the
> > > zswap_stored_pages atomic/zswpout event stats with folio_nr_pages()
> > once,
> > > before returning from zswap_store().
> > >
> > > If an error is encountered during the store of any page in the folio,
> > > all pages in that folio currently stored in zswap will be invalidated.
> > > Thus, a folio is either entirely stored in zswap, or entirely not stored
> > > in zswap.
> > >
> > > The most important value provided by this patch is it enables swapping out
> > > large folios to zswap without splitting them. Furthermore, it batches some
> > > operations while doing so (cgroup charging, stats updates).
> > >
> > > This patch also forms the basis for building compress batching of pages in
> > > a large folio in zswap_store() by compressing up to say, 8 pages of the
> > > folio in parallel in hardware using the Intel In-Memory Analytics
> > > Accelerator (Intel IAA).
> > >
> > > This change reuses and adapts the functionality in Ryan Roberts' RFC
> > > patch [1]:
> > >
> > >   "[RFC,v1] mm: zswap: Store large folios without splitting"
> > >
> > >   [1] https://lore.kernel.org/linux-mm/20231019110543.3284654-1-
> > ryan.roberts@....com/T/#u
> > >
> > > Co-developed-by: Ryan Roberts
> >
> > I would change that to
> >
> > Originally-by: Ryan Roberts <ryan.roberts@....com>
> >
> > > Signed-off-by:
> >
> > and drop this for now.
>
> Thanks Johannes. Sure, this sounds good. Should I post a v11 for just this
> specific patch which this change, or a v11 for the entire series?

Andrew could probably make the change for you while applying the
patches to mm-unstable if you ask nicely :)

Also since we agreed further cleanup can be done as a followup:
Acked-by: Yosry Ahmed <yosryahmed@...gle.com>