On Thu, Apr 19, 2018 at 08:55:47AM -0400, Brian Foster wrote:
> On Tue, Apr 17, 2018 at 07:40:20PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > We've never cached buffers when reading or writing superblocks, so we
> > need to change scrub to do likewise or risk screwing up the uncached sb
> > buffer usage everywhere else.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
>
> Hmm, so this goes back to this[1] thread, right?
Yep.
> IIRC, we wanted to end up with an lru-bypassing uncached buffer lookup
> mechanism to provide uncached behavior for resource-saving purposes
> but without introducing serialization issues between multiple users of
> uncached buffers.
Right.
> On a quick look back, growfs currently uses cached buffers for secondary
> superblocks and the associated patch was looking to change that to
> something like the above. Don't we have the same requirement here (since
> growfs currently still uses cached buffers)?
Correct, this patch is contingent on landing Dave's "tableise growfs"
series that converts growfs to use uncached buffers for writing out the
new secondary supers. If I manage to land Dave's growfs thing before
repair then I'll keep this; if repair goes first I'll defer it to that
series.
I've never done a contingent-patch in the middle of a series, so I'm not
sure exactly how to present such a {monstr,bog}osity.
--D
> Brian
>
> [1] https://marc.info/?l=linux-xfs&m=151746733326282&w=2
>
> > fs/xfs/scrub/agheader.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> >
> > diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
> > index 018aabbd..aacbc3f 100644
> > --- a/fs/xfs/scrub/agheader.c
> > +++ b/fs/xfs/scrub/agheader.c
> > @@ -157,7 +157,7 @@ xfs_scrub_superblock(
> > if (agno == 0)
> > return 0;
> >
> > - error = xfs_trans_read_buf(mp, sc->tp, mp->m_ddev_targp,
> > + error = xfs_buf_read_uncached(mp->m_ddev_targp,
> > XFS_AGB_TO_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
> > XFS_FSS_TO_BB(mp, 1), 0, &bp, &xfs_sb_buf_ops);
> > /*
> > @@ -421,6 +421,7 @@ xfs_scrub_superblock(
> > xfs_scrub_block_set_corrupt(sc, bp);
> >
> > xfs_scrub_superblock_xref(sc, bp);
> > + xfs_buf_relse(bp);
> >
> > return error;
> > }
> >
> > --
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