RE: [PATCH v10 6/7] mm: zswap: Support large folios in zswap_store().

[Sridhar, Kanchana P]

> -----Original Message-----
> From: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> Sent: Tuesday, October 1, 2024 10:34 AM
> To: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx;
> chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx;
> shakeel.butt@xxxxxxxxx; ryan.roberts@xxxxxxx; Huang, Ying
> <ying.huang@xxxxxxxxx>; 21cnbao@xxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx;
> willy@xxxxxxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Feghali, Wajdi K
> <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh <vinodh.gopal@xxxxxxxxx>;
> Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> Subject: RE: [PATCH v10 6/7] mm: zswap: Support large folios in
> zswap_store().
> 
> > -----Original Message-----
> > From: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Sent: Tuesday, October 1, 2024 4:11 AM
> > To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> > yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx;
> > chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx;
> > shakeel.butt@xxxxxxxxx; ryan.roberts@xxxxxxx; Huang, Ying
> > <ying.huang@xxxxxxxxx>; 21cnbao@xxxxxxxxx; akpm@linux-
> foundation.org;
> > willy@xxxxxxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Feghali, Wajdi K
> > <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh <vinodh.gopal@xxxxxxxxx>
> > 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@xxxxxxx/T/#u
> > >
> > > Co-developed-by: Ryan Roberts
> >
> > I would change that to
> >
> > Originally-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> >
> > > Signed-off-by:
> >
> > and drop this for now.
> 
> Hi Andrew,
> 
> Just wanted to check if you can make the change from
> "Co-developed-by/Signed-off-by:" to "Originally-by:" to acknowledge
> Ryan Roberts' contribution, when this patch is included in mm-unstable?
> 
> Please do let me know if it is simpler if I submit a v11 for just this
> specific patch or for the entire series with this change. I will proceed
> based on your recommendation.

Many thanks for adding the "Originally-by:", Andrew! Really appreciate it.

Thanks,
Kanchana

> 
> Thanks,
> Kanchana
> 
> >
> > > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> >
> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>