[Cluster-devel] [GFS2 PATCH 3/3] gfs2: allow fallocate to max out quotas/fs efficiently

[Abhijith Das <adas@redhat.com>]

----- Original Message -----
> From: "Steven Whitehouse" <swhiteho@redhat.com>
> To: "Abhi Das" <adas@redhat.com>, cluster-devel at redhat.com
> Sent: Tuesday, February 17, 2015 3:41:15 AM
> Subject: Re: [Cluster-devel] [GFS2 PATCH 3/3] gfs2: allow fallocate to max out quotas/fs efficiently
> 
> Hi,
> 
> On 16/02/15 17:59, Abhi Das wrote:
> > We can quickly get an estimate of how many more blocks are
> > available for allocation restricted by quota and fs size
> > respectively using the ap->allowed field in the gfs2_alloc_parms
> > structure. gfs2_quota_check() and gfs2_inplace_reserve() provide
> > these values.
> >
> > By re-trying to allocate what's available instead of guessing, we
> > can max out quotas or the filesystem efficiently.
> >
> > Bear in mind that this applies only when the requested fallocate
> > operation would otherwise error out with -EDQUOT or -ENOSPC without
> > utilizing all the blocks that might still be available.
> >
> > Signed-off-by: Abhi Das <adas@redhat.com>
> > ---
> >   fs/gfs2/file.c | 18 +++++++++++-------
> >   1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
> > index 2ea420a..57129fa 100644
> > --- a/fs/gfs2/file.c
> > +++ b/fs/gfs2/file.c
> > @@ -829,20 +829,24 @@ static long __gfs2_fallocate(struct file *file, int
> > mode, loff_t offset, loff_t
> >   			continue;
> >   		}
> >   		ap.target = bytes >> sdp->sd_sb.sb_bsize_shift;
> > +	quota_retry:
> >   		error = gfs2_quota_lock_check(ip, &ap);
> > -		if (error)
> > +		if (error) {
> > +			if (error == -EDQUOT && ap.allowed) {
> > +				bytes = ap.allowed << sdp->sd_sb.sb_bsize_shift;
> > +				ap.target = ap.allowed;
> > +				goto quota_retry;
> > +			}
> >   			return error;
> Do you really need to loop here if -EDQUOT is returned and ap.allowed is
> set? Why not just continue after having updated the target value?
> 
> Otherwise I think these patches look good,
> 
> Steve.
> 

If gfs2_quota_lock_check() fails, the quota isn't locked, which we'd have to do
anyway. And I figured there's a race here where some other process could use up
all or part of ap.allowed blocks before we re-lock the quota thereby causing us
to exceed quotas. So, I decided to retry gfs2_quota_lock_check() itself.

Cheers!
--Abhi