On Wed, Sep 28, 2016 at 12:20:05PM -0400, Brian Foster wrote: > On Tue, Sep 27, 2016 at 07:54:20PM -0700, Darrick J. Wong wrote: > > Every time we allocate or free an extent, we might need to split the > > refcount btree. Reserve some blocks in the transaction to handle > > this possibility. > > > > I'm probably not far along enough to grok how this all works, but I'm a > bit confused by the requirement here. Why is generic block > allocation/free a refcountbt matter? E.g., the function below is used > for things like inode chunk allocation and whatnot, aren't those > irrelevant to the refcountbt? The original reason (pre-deferred ops) was that xfs_allocfree_log_count() was used for calculating log reservations both for user data and for metadata allocation activities, and we tried to cram everything into one giant transaction. As you point out, this can lead to unnecessarily large transaction reservations. Nowadays we roll transactions with deferred ops and the refcount finish_one code preemptively rolls the transaction if it thinks it might be close to the overflow point. I've been thinking we could just remove this since refcount updates are their own transaction anyway. Will try reverting and report back. :) --D > > Brian > > > (Reproduced by generic/167 over NFS atop XFS) > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > [darrick.wong@xxxxxxxxxx: add commit message] > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > --- > > fs/xfs/libxfs/xfs_trans_resv.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c > > index 7c840e1..a59838f 100644 > > --- a/fs/xfs/libxfs/xfs_trans_resv.c > > +++ b/fs/xfs/libxfs/xfs_trans_resv.c > > @@ -67,7 +67,8 @@ xfs_calc_buf_res( > > * Per-extent log reservation for the btree changes involved in freeing or > > * allocating an extent. In classic XFS there were two trees that will be > > * modified (bnobt + cntbt). With rmap enabled, there are three trees > > - * (rmapbt). The number of blocks reserved is based on the formula: > > + * (rmapbt). With reflink, there are four trees (refcountbt). The number of > > + * blocks reserved is based on the formula: > > * > > * num trees * ((2 blocks/level * max depth) - 1) > > * > > @@ -83,6 +84,8 @@ xfs_allocfree_log_count( > > blocks = num_ops * 2 * (2 * mp->m_ag_maxlevels - 1); > > if (xfs_sb_version_hasrmapbt(&mp->m_sb)) > > blocks += num_ops * (2 * mp->m_rmap_maxlevels - 1); > > + if (xfs_sb_version_hasreflink(&mp->m_sb)) > > + blocks += num_ops * (2 * mp->m_refc_maxlevels - 1); > > > > return blocks; > > } > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
