Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
From: Andrew Morton
Date: Wed Nov 19 2014 - 16:15:43 EST
On Wed, 19 Nov 2014 08:52:01 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > >
> > > - /*
> > > - * Return 0 prevents I/O fallback trial caused by rw_page fail
> > > - * and upper layer can handle this IO error via page error.
> > > - */
> > > + page_endio(page, rw, 0);
> > > return 0;
> > Losing the comment makes me sad. The code is somewhat odd-looking. We
> > should add some words explaining why we're not reporting errors at this
> > point.
> Okay. How about this?
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index decca6f161b8..1d7c90d5e0d0 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -975,6 +975,12 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
> err = zram_bvec_rw(zram, &bv, index, offset, rw);
> + /*
> + * If I/O fails, just return error without calling page_endio.
> + * It causes resubmit the I/O with bio request by rw_page fallback
> + * and bio I/O complete handler does things to handle the error
> + * (e.g., set_page_dirty of swap_writepage fail).
> + */
> if (err == 0)
> page_endio(page, rw, 0);
> return err;
I don't understand the comment :( bdev_read_page() doesn't resubmit the
IO if block_device_operations.rw_page() returns zero and it's unclear
how the bio I/O complete handler (which one?) gets involved.
It would help in the comment was more specific. Instead of using vague
terms like "rw_page fallback" and "bio I/O complete handler", use
actual function names so the reader understand exactly what code we're
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