linux-kernel - Re: [PATCH v3 2/4] zsmalloc: change return value unit of zs_get_total_size

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Message-ID: <20140821232319.GG10703@gmail.com>
Date:	Thu, 21 Aug 2014 23:23:19 +0000
From:	Minchan Kim <minchan@...nel.org>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com,
	seungho1.park@....com, Luigi Semenzato <semenzato@...gle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	David Horner <ds2horner@...il.com>
Subject: Re: [PATCH v3 2/4] zsmalloc: change return value unit of
 zs_get_total_size_bytes

On Thu, Aug 21, 2014 at 02:53:57PM -0400, Dan Streetman wrote:
> On Wed, Aug 20, 2014 at 8:27 PM, Minchan Kim <minchan@...nel.org> wrote:
> > zs_get_total_size_bytes returns a amount of memory zsmalloc
> > consumed with *byte unit* but zsmalloc operates *page unit*
> > rather than byte unit so let's change the API so benefit
> > we could get is that reduce unnecessary overhead
> > (ie, change page unit with byte unit) in zsmalloc.
> >
> > Now, zswap can rollback to zswap_pool_pages.
> > Over to zswap guys ;-)
> 
> We could change zpool/zswap over to total pages instead of total
> bytes, since both zbud and zsmalloc now report size in pages.  The
> only downside would be if either changed later to not use only whole
> pages (or if they start using huge pages for storage...), but for what
> they do that seems unlikely.  After this patch is finalized I can
> write up a quick patch unless Seth disagrees (or already has a patch
> :)
> 
> >
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
> >  drivers/block/zram/zram_drv.c |  4 ++--
> >  include/linux/zsmalloc.h      |  2 +-
> >  mm/zsmalloc.c                 | 10 +++++-----
> >  3 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index d00831c3d731..302dd37bcea3 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -103,10 +103,10 @@ static ssize_t mem_used_total_show(struct device *dev,
> >
> >         down_read(&zram->init_lock);
> >         if (init_done(zram))
> > -               val = zs_get_total_size_bytes(meta->mem_pool);
> > +               val = zs_get_total_size(meta->mem_pool);
> >         up_read(&zram->init_lock);
> >
> > -       return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
> > +       return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
> >  }
> >
> >  static ssize_t max_comp_streams_show(struct device *dev,
> > diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
> > index e44d634e7fb7..105b56e45d23 100644
> > --- a/include/linux/zsmalloc.h
> > +++ b/include/linux/zsmalloc.h
> > @@ -46,6 +46,6 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> >                         enum zs_mapmode mm);
> >  void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
> >
> > -u64 zs_get_total_size_bytes(struct zs_pool *pool);
> > +unsigned long zs_get_total_size(struct zs_pool *pool);
> 
> minor naming suggestion, but since the name is changing anyway,
> "zs_get_total_size" implies to me the units are bytes, would
> "zs_get_total_pages" be clearer that it's returning size in # of
> pages, not bytes?

It's better. Will change.
Thanks!
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