Re: [PATCH] Btrfs: do not backup tree roots when fsync

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On Thu, Sep 14, 2017 at 09:55:48AM +0800, Qu Wenruo wrote:
> 
> 
> On 2017年09月14日 02:25, Liu Bo wrote:
> > It doens't make sense to backup tree roots when doing fsync, since
> > during fsync those tree roots have not been consistent on disk.
> > 
> > Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> 
> Reviewed-by: Qu Wenruo <quwenruo.btrfs@xxxxxxx>
> 
> With a pit can be improved.
> > ---
> >   fs/btrfs/disk-io.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 79ac228..a145a88 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -3668,7 +3668,14 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
> >   	u64 flags;
> >   
> >   	do_barriers = !btrfs_test_opt(fs_info, NOBARRIER);
> > -	backup_super_roots(fs_info);
> > +
> > +	/*
> > +	 * max_mirrors == 0 indicates we're from commit_transaction,
> > +	 * not from fsync where the tree roots in fs_info have not
> > +	 * been consistent on disk.
> > +	 */
> > +	if (max_mirrors == 0)
> > +		backup_super_roots(fs_info);
> 
> BTW, the @max_mirrors naming here is really confusing.
> Normally I would expect max_mirrors == 0 means we don't need to backup 
> super roots...

Agreed it's confusing, could be something like "bool write_backups" (in a
separate patch).
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