linux-kernel - Re: [PATCH] driver: zram: fix wrong counting on pages

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Message-ID: <YP72sNSOVwgnQzqo@google.com>
Date:   Mon, 26 Jul 2021 10:53:52 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Huangzhaoyang <huangzhaoyang@...il.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH] driver: zram: fix wrong counting on pages_store

On Mon, Jul 26, 2021 at 10:27:40AM +0900, Sergey Senozhatsky wrote:
> On (21/07/20 14:47), Huangzhaoyang wrote:
> > It makes the statistic confused when counting pages_store in during writeback.
> > pages_store should just reflect the swapped pages on ZRAM, while bd_writes be
> > responsible for writeback things.
> > 
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > ---
> >  drivers/block/zram/zram_drv.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index cf8deec..6bdaa9d 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -765,7 +765,6 @@ static ssize_t writeback_store(struct device *dev,
> >  		zram_set_flag(zram, index, ZRAM_WB);
> >  		zram_set_element(zram, index, blk_idx);
> >  		blk_idx = 0;
> > -		atomic64_inc(&zram->stats.pages_stored);
> 
> Yeah, I think we don't need it here.
> 
> Minchan, what do you think?

What pages_stored currently represents is orig_data_size from mm_stat

 ================ =============================================================
 orig_data_size   uncompressed size of data stored in this disk.
                  Unit: bytes

Thus, if we don't increase it after zram_free_page, it loses what's
the original data size which would be important to calculate
compression ratio along with compr_data_size.