RE: [RFC PATCH v1 13/13] mm: vmscan, swap, zswap: Compress batching of folios in shrink_folio_list().

[Sridhar, Kanchana P]

Hi Joel,

> -----Original Message-----
> From: Joel Granados <joel.granados@xxxxxxxxxx>
> Sent: Monday, October 28, 2024 7:42 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> hannes@xxxxxxxxxxx; yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx;
> chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx;
> ryan.roberts@xxxxxxx; Huang, Ying <ying.huang@xxxxxxxxx>;
> 21cnbao@xxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; linux-
> crypto@xxxxxxxxxxxxxxx; herbert@xxxxxxxxxxxxxxxxxxx;
> davem@xxxxxxxxxxxxx; clabbe@xxxxxxxxxxxx; ardb@xxxxxxxxxx;
> ebiggers@xxxxxxxxxx; surenb@xxxxxxxxxx; Accardi, Kristen C
> <kristen.c.accardi@xxxxxxxxx>; zanussi@xxxxxxxxxx; viro@xxxxxxxxxxxxxxxxxx;
> brauner@xxxxxxxxxx; jack@xxxxxxx; mcgrof@xxxxxxxxxx; kees@xxxxxxxxxx;
> bfoster@xxxxxxxxxx; willy@xxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> Feghali, Wajdi K <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh
> <vinodh.gopal@xxxxxxxxx>
> Subject: Re: [RFC PATCH v1 13/13] mm: vmscan, swap, zswap: Compress
> batching of folios in shrink_folio_list().
> 
> On Thu, Oct 17, 2024 at 11:41:01PM -0700, Kanchana P Sridhar wrote:
> > This patch enables the use of Intel IAA hardware compression acceleration
> > to reclaim a batch of folios in shrink_folio_list(). This results in
> > reclaim throughput and workload/sys performance improvements.
> >
> > The earlier patches on compress batching deployed multiple IAA compress
> > engines for compressing up to SWAP_CRYPTO_SUB_BATCH_SIZE pages
> within a
> > large folio that is being stored in zswap_store(). This patch further
> > propagates the efficiency improvements demonstrated with IAA "batching
> > within folios", to vmscan "batching of folios" which will also use
> > batching within folios using the extensible architecture of
> > the __zswap_store_batch_core() procedure added earlier, that accepts
> > an array of folios.
> 
> ...
> 
> > +static inline void zswap_store_batch(struct swap_in_memory_cache_cb
> *simc)
> > +{
> > +}
> > +
> >  static inline bool zswap_store(struct folio *folio)
> >  {
> >  	return false;
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 79e6cb1d5c48..b8d6b599e9ae 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -2064,6 +2064,15 @@ static struct ctl_table vm_table[] = {
> >  		.extra1		= SYSCTL_ZERO,
> >  		.extra2		= (void *)&page_cluster_max,
> >  	},
> > +	{
> > +		.procname	= "compress-batchsize",
> > +		.data		= &compress_batchsize,
> > +		.maxlen		= sizeof(int),
> > +		.mode		= 0644,
> > +		.proc_handler	= proc_dointvec_minmax,
> Why not use proc_douintvec_minmax? These are the reasons I think you
> should use that (please correct me if I miss-read your patch):
> 
> 1. Your range is [1,32] -> so no negative values
> 2. You are using the value to compare with an unsinged int
>    (simc->nr_folios) in your `struct swap_in_memory_cache_cb`. So
>    instead of going from int to uint, you should just do uint all
>    around. No?
> 3. Using proc_douintvec_minmax will automatically error out on negative
>    input without event considering your range, so there is less code
>    executed at the end.

Thanks for your code review comments! Sure, what you suggest makes
sense. Based on Yosry's suggestions, I plan to separate out the
batching reclaim shrink_folio_list() changes into a separate series, and
focus on just the zswap modifications to support large folio compression
batching in the initial series. I will make sure to incorporate your comments
in the shrink_folio_list() batching reclaim series.

Thanks,
Kanchana

> 
> > +		.extra1		= SYSCTL_ONE,
> > +		.extra2		= (void *)&compress_batchsize_max,
> > +	},
> >  	{
> >  		.procname	= "dirtytime_expire_seconds",
> >  		.data		= &dirtytime_expire_interval,
> > diff --git a/mm/page_io.c b/mm/page_io.c
> > index a28d28b6b3ce..065db25309b8 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -226,6 +226,131 @@ static void swap_zeromap_folio_clear(struct folio
> *folio)
> >  	}
> >  }
> 
> ...
> 
> Best
> 
> --
> 
> Joel Granados