On Tue, Jul 07, 2020 at 08:59:06AM -0400, Brian Foster wrote:
> On Thu, Jul 02, 2020 at 08:27:09AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > In commit 9851fd79bfb1, we added a slight amount of slack to the free
> > space btrees being reconstructed so that the initial fix_freelist call
> > (which is run against a totally empty AGFL) would never have to split
> > either free space btree in order to populate the free list.
> >
> > The new btree bulk loading code in xfs_repair can re-create this
> > situation because it can set the slack values to zero if the filesystem
> > is very full. However, these days repair has the infrastructure needed
> > to ensure that overestimations of the btree block counts end up on the
> > AGFL or get freed back into the filesystem at the end of phase 5.
> >
> > Fix this problem by reserving extra blocks in the bnobt reservation, and
> > checking that there are enough overages in the bnobt/cntbt fakeroots to
> > populate the AGFL with the minimum number of blocks it needs to handle a
> > split in the bno/cnt/rmap btrees.
> >
> > Note that we reserve blocks for the new bnobt/cntbt/AGFL at the very end
> > of the reservation steps in phase 5, so the extra allocation should not
> > cause repair to fail if it can't find blocks for btrees.
> >
> > Fixes: 9851fd79bfb1 ("repair: AGFL rebuild fails if btree split required")
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > repair/agbtree.c | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
> > 1 file changed, 44 insertions(+), 7 deletions(-)
> >
> >
> > diff --git a/repair/agbtree.c b/repair/agbtree.c
> > index de8015ec..9f64d54b 100644
> > --- a/repair/agbtree.c
> > +++ b/repair/agbtree.c
> ...
> > @@ -268,16 +288,33 @@ _("Unable to compute free space by length btree geometry, error %d.\n"), -error)
> > btr_cnt->bload.nr_blocks;
> >
> > /* We don't need any more blocks, so we're done. */
> > - if (delta_bno >= 0 && delta_cnt >= 0) {
> > + if (delta_bno >= 0 && delta_cnt >= 0 &&
> > + delta_bno + delta_cnt >= agfl_goal) {
> > *extra_blocks = delta_bno + delta_cnt;
> > break;
> > }
> >
> > /* Allocate however many more blocks we need this time. */
> > - if (delta_bno < 0)
> > + if (delta_bno < 0) {
> > reserve_btblocks(sc->mp, agno, btr_bno, -delta_bno);
> > - if (delta_cnt < 0)
> > + delta_bno = 0;
> > + }
> > + if (delta_cnt < 0) {
> > reserve_btblocks(sc->mp, agno, btr_cnt, -delta_cnt);
> > + delta_cnt = 0;
> > + }
> > +
> > + /*
> > + * Try to fill the bnobt cursor with extra blocks to populate
> > + * the AGFL. If we don't get all the blocks we want, stop
> > + * trying to fill the AGFL because the AG is totally out of
> > + * space.
> > + */
> > + agfl_wanted = agfl_goal - (delta_bno + delta_cnt);
> > + if (agfl_wanted > 0 &&
> > + agfl_wanted != reserve_agblocks(sc->mp, agno, btr_bno,
> > + agfl_wanted))
> > + agfl_goal = 0;
>
> Nit: can we split off the function call so it's not embedded in the if
> condition? With that tweak:
It occurs to me that we don't care how much we fall short of the
requested allocation. I could change reserve_agblocks to return true if
it got all the blocks it was asked to get, and then that becomes:
if (agfl_wanted > 0 &&
!reserve_agblocks(sc->mp, agno, btr_bno, agfl_wanted)
agfl_goal = 0;
How does that sound?
--D
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
>
> >
> > /* Ok, now how many free space records do we have? */
> > *nr_extents = count_bno_extents_blocks(agno, &num_freeblocks);
> >
>
