Re: [PATCH] Btrfs: fix enospc in punch hole

From: Filipe Manana <fdmanana@gmail.com>
To: robbieko <robbieko@synology.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] Btrfs: fix enospc in punch hole
Date: Fri, 7 Oct 2016 11:18:03 +0100	[thread overview]
Message-ID: <CAL3q7H4rQq_yC6PsohCN=9XAU8QTauQhhxB2sKRe+OEZqmQVUA@mail.gmail.com> (raw)
In-Reply-To: <1475820576-27316-1-git-send-email-robbieko@synology.com>

On Fri, Oct 7, 2016 at 7:09 AM, robbieko <robbieko@synology.com> wrote:
> From: Robbie Ko <robbieko@synology.com>
>
> when extent-tree level > BTRFS_MAX_LEVEL / 2,
> __btrfs_drop_extents -> btrfs_duplicate_item ->
> setup_leaf_for_split -> split_leaf
> maybe enospc, because min_size is too small,
> need use btrfs_calc_trans_metadata_size.

This change log is terrible.
You should describe the problem and fix. That is, that hole punching
can result in adding new leafs (and as a consequence new nodes) to the
tree because when we find file extent items that span beyond the hole
range we may end up not deleting them (just adjusting them) and add
new file extent items representing holes.

And I don't see why this is exclusive for the case where the height of
the extent tree is greater than 4 (BTRFS_MAX_LEVEL / 2).

The code changes themselves look good to me.

thanks

>
> Signed-off-by: Robbie Ko <robbieko@synology.com>
> ---
>  fs/btrfs/file.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index fea31a4..809ca85 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2322,7 +2322,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>         u64 tail_len;
>         u64 orig_start = offset;
>         u64 cur_offset;
> -       u64 min_size = btrfs_calc_trunc_metadata_size(root, 1);
> +       u64 min_size = btrfs_calc_trans_metadata_size(root, 1);
>         u64 drop_end;
>         int ret = 0;
>         int err = 0;
> @@ -2469,7 +2469,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>                 ret = -ENOMEM;
>                 goto out_free;
>         }
> -       rsv->size = btrfs_calc_trunc_metadata_size(root, 1);
> +       rsv->size = btrfs_calc_trans_metadata_size(root, 1);
>         rsv->failfast = 1;
>
>         /*
> --
> 1.9.1
>
> --
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-- 
Filipe David Manana,

"People will forget what you said,
 people will forget what you did,
 but people will never forget how you made them feel."