Re: [PATCH 07/42] btrfs: check if free bgs for commit

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Oct 04, 2018 at 01:24:24PM +0200, David Sterba wrote:
> On Fri, Sep 28, 2018 at 07:17:46AM -0400, Josef Bacik wrote:
> > may_commit_transaction will skip committing the transaction if we don't
> > have enough pinned space or if we're trying to find space for a SYSTEM
> > chunk.  However if we have pending free block groups in this transaction
> > we still want to commit as we may be able to allocate a chunk to make
> > our reservation.  So instead of just returning ENOSPC, check if we have
> > free block groups pending, and if so commit the transaction to allow us
> > to use that free space.
> > 
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > Reviewed-by: Omar Sandoval <osandov@fb.com>
> > ---
> >  fs/btrfs/extent-tree.c | 33 +++++++++++++++++++--------------
> >  1 file changed, 19 insertions(+), 14 deletions(-)
> > 
> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> > index 1213f573eea2..da73b3e5bc39 100644
> > --- a/fs/btrfs/extent-tree.c
> > +++ b/fs/btrfs/extent-tree.c
> > @@ -4830,10 +4830,18 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
> >  	if (!bytes)
> >  		return 0;
> >  
> > -	/* See if there is enough pinned space to make this reservation */
> > -	if (__percpu_counter_compare(&space_info->total_bytes_pinned,
> > -				   bytes,
> > -				   BTRFS_TOTAL_BYTES_PINNED_BATCH) >= 0)
> > +	trans = btrfs_join_transaction(fs_info->extent_root);
> > +	if (IS_ERR(trans))
> > +		return -ENOSPC;
> 
> Why do you set override the error to ENOSPC, instead of passing
> PTR_ERR(trans)? There are more reasons why btrfs_join_transaction could
> fail: EROFS after error, EDQUOT when quotas say no, ENOMEM from
> ulist_add, that's just a sample I quickly found.

(argh I hit r instead of g, sending again)

Because may_commit_transaction is only called during flushing, we don't actually
care about the value, just that it failed.  Thanks,

Josef