linux-kernel - Re: [PATCH 1/5] zram: remove the call to page_endio in the bio end

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Date:   Thu, 30 Mar 2023 15:51:54 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Pankaj Raghav <p.raghav@...sung.com>
Cc:     martin@...ibond.com, axboe@...nel.dk, akpm@...ux-foundation.org,
        hubcap@...ibond.com, willy@...radead.org, viro@...iv.linux.org.uk,
        senozhatsky@...omium.org, brauner@...nel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        mcgrof@...nel.org, linux-block@...r.kernel.org,
        gost.dev@...sung.com, linux-mm@...ck.org, devel@...ts.orangefs.org
Subject: Re: [PATCH 1/5] zram: remove the call to page_endio in the bio
 end_io handler

On Tue, Mar 28, 2023 at 01:27:12PM +0200, Pankaj Raghav wrote:
> zram_page_end_io function is called when alloc_page is used (for
> partial IO) to trigger writeback from the user space. The pages used for

No, it was used with zram_rw_page since rw_page didn't carry the bio.

> this operation is never locked or have the writeback set. So, it is safe

VM had the page lock and wait to unlock.

> to remove the call to page_endio() function that unlocks or marks
> writeback end on the page.
> 
> Rename the endio handler from zram_page_end_io to zram_read_end_io as
> the call to page_endio() is removed and to associate the callback to the
> operation it is used in.

Since zram removed the rw_page and IO comes with bio from now on,
IIUC, we are fine since every IO will go with chained-IO. Right?

> 
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  drivers/block/zram/zram_drv.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b7bb52f8dfbd..3300e7eda2f6 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -606,12 +606,8 @@ static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
>  	atomic64_dec(&zram->stats.bd_count);
>  }
>  
> -static void zram_page_end_io(struct bio *bio)
> +static void zram_read_end_io(struct bio *bio)
>  {
> -	struct page *page = bio_first_page_all(bio);
> -
> -	page_endio(page, op_is_write(bio_op(bio)),
> -			blk_status_to_errno(bio->bi_status));
>  	bio_put(bio);
>  }
>  
> @@ -635,7 +631,7 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
>  	}
>  
>  	if (!parent)
> -		bio->bi_end_io = zram_page_end_io;
> +		bio->bi_end_io = zram_read_end_io;
>  	else
>  		bio_chain(bio, parent);
>  
> -- 
> 2.34.1
>