Hello, On Wed, Nov 19, 2014 at 01:15:35PM -0800, Andrew Morton wrote: > 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); > > out_unlock: > > up_read(&zram->init_lock); > > + /* > > + * 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 It's not bdev_read_page but upper functions. (ie, do_mpage_readpage, swap_readpage, __mpage_writepage, __swap_writepage) > how the bio I/O complete handler (which one?) gets involved. bio->bi_end_io. > > 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 > referring to. Indeed. I was terrible. Hope this is better. >From 635f22cac08f76b909ccc13b2de0b5d437eef5aa Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@xxxxxxxxxx> Date: Wed, 19 Nov 2014 08:57:49 +0900 Subject: [PATCH] zram: add comment Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index decca6f161b8..6f1ceb14e64b 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -975,6 +975,14 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, err = zram_bvec_rw(zram, &bv, index, offset, rw); out_unlock: up_read(&zram->init_lock); + /* + * If I/O fails, just return error(ie, non-zero) without + * calling page_endio. + * It causes resubmit the I/O with bio request by upper functions + * of rw_page(e.g., swap_readpage, __swap_writepage) and + * bio->bi_end_io does things to handle the error + * (e.g., SetPageError, set_page_dirty and extra works). + */ if (err == 0) page_endio(page, rw, 0); return err; -- 2.0.0 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>