RE: [PATCH v8 5/8] mm: zswap: Modify zswap_stored_pages to be atomic_long_t.

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

> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@google.com>
> Sent: Saturday, September 28, 2024 1:13 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; nphamcs@gmail.com; chengming.zhou@linux.dev;
> usamaarif642@gmail.com; shakeel.butt@linux.dev; 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 v8 5/8] mm: zswap: Modify zswap_stored_pages to be
> atomic_long_t.
> 
> On Fri, Sep 27, 2024 at 7:16 PM Kanchana P Sridhar
> <kanchana.p.sridhar@intel.com> wrote:
> >
> > For zswap_store() to support large folios, we need to be able to do
> > a batch update of zswap_stored_pages upon successful store of all pages
> > in the folio. For this, we need to add folio_nr_pages(), which returns
> > a long, to zswap_stored_pages.
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
> > ---
> >  fs/proc/meminfo.c     |  2 +-
> >  include/linux/zswap.h |  2 +-
> >  mm/zswap.c            | 19 +++++++++++++------
> >  3 files changed, 15 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> > index 245171d9164b..8ba9b1472390 100644
> > --- a/fs/proc/meminfo.c
> > +++ b/fs/proc/meminfo.c
> > @@ -91,7 +91,7 @@ static int meminfo_proc_show(struct seq_file *m,
> void *v)
> >  #ifdef CONFIG_ZSWAP
> >         show_val_kb(m, "Zswap:          ", zswap_total_pages());
> >         seq_printf(m,  "Zswapped:       %8lu kB\n",
> > -                  (unsigned long)atomic_read(&zswap_stored_pages) <<
> > +                  (unsigned long)atomic_long_read(&zswap_stored_pages) <<
> 
> Do we still need this cast? "HardwareCorrupted" seems to be using
> atomic_long_read() without a cast.
> 
> Otherwise this LGTM:
> Acked-by: Yosry Ahmed <yosryahmed@google.com>

Thanks Yosry for the Acked-by's!

Thanks,
Kanchana

> 
> >                    (PAGE_SHIFT - 10));
> >  #endif
> >         show_val_kb(m, "Dirty:          ",
> > diff --git a/include/linux/zswap.h b/include/linux/zswap.h
> > index 9cd1beef0654..d961ead91bf1 100644
> > --- a/include/linux/zswap.h
> > +++ b/include/linux/zswap.h
> > @@ -7,7 +7,7 @@
> >
> >  struct lruvec;
> >
> > -extern atomic_t zswap_stored_pages;
> > +extern atomic_long_t zswap_stored_pages;
> >
> >  #ifdef CONFIG_ZSWAP
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 0f281e50a034..43e4e216db41 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -43,7 +43,7 @@
> >  * statistics
> >  **********************************/
> >  /* The number of compressed pages currently stored in zswap */
> > -atomic_t zswap_stored_pages = ATOMIC_INIT(0);
> > +atomic_long_t zswap_stored_pages = ATOMIC_INIT(0);
> >
> >  /*
> >   * The statistics below are not protected from concurrent access for
> > @@ -802,7 +802,7 @@ static void zswap_entry_free(struct zswap_entry
> *entry)
> >                 obj_cgroup_put(entry->objcg);
> >         }
> >         zswap_entry_cache_free(entry);
> > -       atomic_dec(&zswap_stored_pages);
> > +       atomic_long_dec(&zswap_stored_pages);
> >  }
> >
> >  /*********************************
> > @@ -1232,7 +1232,7 @@ static unsigned long zswap_shrinker_count(struct
> shrinker *shrinker,
> >                 nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
> >         } else {
> >                 nr_backing = zswap_total_pages();
> > -               nr_stored = atomic_read(&zswap_stored_pages);
> > +               nr_stored = atomic_long_read(&zswap_stored_pages);
> >         }
> >
> >         if (!nr_stored)
> > @@ -1501,7 +1501,7 @@ bool zswap_store(struct folio *folio)
> >         }
> >
> >         /* update stats */
> > -       atomic_inc(&zswap_stored_pages);
> > +       atomic_long_inc(&zswap_stored_pages);
> >         count_vm_event(ZSWPOUT);
> >
> >         return true;
> > @@ -1650,6 +1650,13 @@ static int debugfs_get_total_size(void *data,
> u64 *val)
> >  }
> >  DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size,
> NULL, "%llu\n");
> >
> > +static int debugfs_get_stored_pages(void *data, u64 *val)
> > +{
> > +       *val = atomic_long_read(&zswap_stored_pages);
> > +       return 0;
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(stored_pages_fops,
> debugfs_get_stored_pages, NULL, "%llu\n");
> > +
> >  static int zswap_debugfs_init(void)
> >  {
> >         if (!debugfs_initialized())
> > @@ -1673,8 +1680,8 @@ static int zswap_debugfs_init(void)
> >                            zswap_debugfs_root, &zswap_written_back_pages);
> >         debugfs_create_file("pool_total_size", 0444,
> >                             zswap_debugfs_root, NULL, &total_size_fops);
> > -       debugfs_create_atomic_t("stored_pages", 0444,
> > -                               zswap_debugfs_root, &zswap_stored_pages);
> > +       debugfs_create_file("stored_pages", 0444,
> > +                           zswap_debugfs_root, NULL, &stored_pages_fops);
> >
> >         return 0;
> >  }
> > --
> > 2.27.0
> >