On Wednesday, February 15, 2017 11:03:11 AM Eric Sandeen wrote:
> On 2/15/17 10:13 AM, Eric Sandeen wrote:
> >> The root cause of the problem is due to the fact that
> >> xfs_sb_version_hasalign() returns true when we are working on a V5
> >> filesystem. Due to this args.minalignslop (in xfs_ialloc_ag_alloc())
> >> gets the unsigned equivalent of -1 assigned to it. This later causes
> >> alloc_len in xfs_alloc_space_available() to have a value of 0. In such a
> >> scenario when args.total is also 0, the assert statement
> >> "ASSERT(args->maxlen > 0);" fails.
> > Hm, the intent of the _haslign() function is to say that V5 must always
> > imply the "alignbit" - i.e. we don't want to grow an infinite feature
> > matrix, and by the time you get to V5 supers, there are many things which
> > cannot be turned on or off, such as this feature.
> >
> > So what happens here... xfs_ialloc_ag_alloc does:
> >
> > args.minalignslop = xfs_ialloc_cluster_alignment(args.mp) - 1;
> >
> > so you're saying that cluster_alignment comes out as 0?
> >
> > That function is checking _hasalign:
> >
> > static inline int
> > xfs_ialloc_cluster_alignment(
> > struct xfs_mount *mp)
> > {
> > if (xfs_sb_version_hasalign(&mp->m_sb) &&
> > mp->m_sb.sb_inoalignmt >=
> > XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size))
> > return mp->m_sb.sb_inoalignmt;
> > return 1;
> > }
> >
> > So are you saying that this function returns 0? That would imply that
> > sb_inoalignmt and m_inode_cluster_size are both zero, yes? Is this
> > what you see?
>
> Sorry, I guess that means XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size)) is
> zero; inode cluster size is 8192 in this case I think, and that is in fact
> 0 filesystem blocks when computed with this macro.
Yes, sb_inoalignmt is indeed 0 because of the following code from
main() in xfsprogs/mkfs/xfs_mkfs.c,
if (sb_feat.inode_align) {
int cluster_size = XFS_INODE_BIG_CLUSTER_SIZE;
if (sb_feat.crcs_enabled)
cluster_size *= isize / XFS_DINODE_MIN_SIZE;
sbp->sb_inoalignmt = cluster_size >> blocklog;
sb_feat.inode_align = sbp->sb_inoalignmt != 0;
}
And XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size)) returns 0 as well. Hence the
condition (xfs_sb_version_hasalign(&mp->m_sb) && mp->m_sb.sb_inoalignmt >=
XFS_B_TO_FSBT(mp, mp->m_inode_cluster_size)) evaluates to true.
>
> I need to think about this a little bit to convince myself that the inode
> alignment bit really /should/ be off for a filesystem of this geometry, vs
> changing the macro to recognize the case.
>
> -Eric
>
--
chandan
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