linux-kernel - Re: [PATCH] btrfs:remove redundant index_rbio_pages in raid56_rmw

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Date:   Thu, 29 Sep 2022 11:08:10 +0800
From:   Qu Wenruo <wqu@...e.com>
To:     "Flint.Wang" <hmsjwzb@...o.com>
Cc:     stringbox8@...o.com, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs:remove redundant index_rbio_pages in
 raid56_rmw_stripe



On 2022/9/29 09:44, Flint.Wang wrote:
>    The index_rbio_pages in raid56_rmw_stripe is redundant.

index_rbio_pages() is to populate the rbio->bio_sectors array.

In raid56_rmw_stripe() we later calls sector_in_rbio(), which will check 
if a sector is belonging to bio_lists.

If not called, all sector will be returned using the sectors in 
rbio->bio_sectors, not using the sectors in bio lists.

Have you tried your patch with fstests runs?

IMHO it should fail a lot of very basic writes in RAID56.

Thanks,
Qu

>    It is invoked in finish_rmw anyway.
> 
> Signed-off-by: Flint.Wang <hmsjwzb@...o.com>
> ---
>   fs/btrfs/raid56.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> index f6395e8288d69..44266b2c5b86e 100644
> --- a/fs/btrfs/raid56.c
> +++ b/fs/btrfs/raid56.c
> @@ -1546,8 +1546,6 @@ static int raid56_rmw_stripe(struct btrfs_raid_bio *rbio)
>   	if (ret)
>   		goto cleanup;
>   
> -	index_rbio_pages(rbio);
> -
>   	atomic_set(&rbio->error, 0);
>   	/* Build a list of bios to read all the missing data sectors. */
>   	for (total_sector_nr = 0; total_sector_nr < nr_data_sectors;