Re: [Ocfs2-devel] [PATCH 4/6] ocfs2: budget for extent tree splits when adding refcount flag

From: Darwin <darwin.xupt@gmail.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: mfasheh@versity.com, jlbec@evilplan.org,
	linux-fsdevel@vger.kernel.org,
	ocfs2-devel <ocfs2-devel@oss.oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH 4/6] ocfs2: budget for extent tree splits when adding refcount flag
Date: Thu, 10 Nov 2016 17:20:27 +0800	[thread overview]
Message-ID: <CACbbJyYped4uF9rnEJ0RZ5dK54e8PAo8jamHpcWznb5obJ_bOw@mail.gmail.com> (raw)
In-Reply-To: <147873189167.2820.5870521669010779004.stgit@birch.djwong.org>

Hello,

On Thu, Nov 10, 2016 at 6:51 AM, Darrick J. Wong
<darrick.wong@oracle.com> wrote:
> When we're adding the refcount flag to an extent, we have to budget
> enough space to handle a full extent btree split in addition to

May I ask some questions (possibly stupid):
1) why and when would extend btree split? From my understanding, if I do

$cp --reflink a b

a is not inline-data. refcount tree will be allocated, every extent
record of "a" will refer to
refcount record respectively and be marked with refcounted, operations
like this also for "b".
So, I think splitting only happens when writing on them, CMIIW;-)

2) what do you mean by "*full* extent btree"?

> whatever modifications have to be made to the refcount btree.  We
> don't currently do this, with the result that generic/186 crashes
> when we need an extent split but not a refcount split because meta_ac
> never gets allocated.

3) in what situation, will this happen? - "we need an extent split but
not a refcount split".
Could you please explain more by example?

Thanks,
Darwin

>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/ocfs2/refcounttree.c |    3 +++
>  1 file changed, 3 insertions(+)
>
>
> diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
> index 59be8f4..d92b6c6 100644
> --- a/fs/ocfs2/refcounttree.c
> +++ b/fs/ocfs2/refcounttree.c
> @@ -3698,6 +3698,9 @@ int ocfs2_add_refcount_flag(struct inode *inode,
>         struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>         struct ocfs2_alloc_context *meta_ac = NULL;
>
> +       /* We need to be able to handle at least an extent tree split. */
> +       ref_blocks = ocfs2_extend_meta_needed(data_et->et_root_el);
> +
>         ret = ocfs2_calc_refcount_meta_credits(inode->i_sb,
>                                                ref_ci, ref_root_bh,
>                                                p_cluster, num_clusters,
>
>
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel@oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel

-- 
Thanks,
Darwin