Account for inode cluster alignment in all allocations
At ENOSPC, we can get a filesystem shutdown due to a cancelling a
dirty transaction in xfs_mkdir or xfs_create. This is due to the
initial allocation attempt not taking into account inode alignment and hence
we can prepare the AGF freelist for allocation when it's not actually
possible to do an allocation. This results in inode allocation returning
ENOSPC with a dirty transaction, and hence we shut down the filesystem.
Because the first allocation is an exact allocation attempt, we must tell
the allocator that the alignment does not affect the allocation attempt.
i.e. we will accept any extent alignment as long as the extent starts
at the block we want. Unfortunately, this means that if the longest
free extent is less than the length + alignment necessary for fallback
allocation attempts but is long enough to attempt a non-aligned allocation,
we will modify the free list.
If we then have the exact allocation fail, all other allocation attempts
will also fail due to the alignment constraint being taken into account.
Hence the initial attempt needs to set the "alignment slop" field so
that alignment, while not required, must be taken into account when
determining if there is enough space left in the AG to do the allocation.
That means if the exact allocation fails, we will not dirty the freelist
if there is not enough space available fo a subsequent allocation to
succeed. Hence we get an ENOSPC error back to userspace without shutting
down the filesystem.
Date: Tue Mar 25 15:13:28 AEDT 2008
Inspected by: hch@xxxxxxxxxxxxx
The following file(s) were checked into:
fs/xfs/xfs_ialloc.c - 1.198 - changed
- Account for inode cluster allocation alignment even when trying to
at an exact block. This prevents a failed exact allocation attempt
dirtying the transaction when the conditions are such that no