xfs: try to avoid blowing out the transaction reservation when bunmaping a shared extent
In a pathological scenario where we are trying to bunmapi a single
extent in which every other block is shared, it's possible that trying
to unmap the entire large extent in a single transaction can generate so
many EFIs that we overflow the transaction reservation.
Therefore, use a heuristic to guess at the number of blocks we can
safely unmap from a reflink file's data fork in an single transaction.
This should prevent problems such as the log head slamming into the tail
and ASSERTs that trigger because we've exceeded the transaction
reservation.
Note that since bunmapi can fail to unmap the entire range, we must also
teach the deferred unmap code to roll into a new transaction whenever we
get low on reservation.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
[hch: random edits, all bugs are my fault]
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index a7048eaf..19480ed 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5434,6 +5434,7 @@ __xfs_bunmapi(
int whichfork; /* data or attribute fork */
xfs_fsblock_t sum;
xfs_filblks_t len = *rlen; /* length to unmap in file */
+ xfs_fileoff_t max_len;
trace_xfs_bunmap(ip, bno, len, flags, _RET_IP_);
@@ -5455,6 +5456,16 @@ __xfs_bunmapi(
ASSERT(len > 0);
ASSERT(nexts >= 0);
+ /*
+ * Guesstimate how many blocks we can unmap without running the risk of
+ * blowing out the transaction with a mix of EFIs and reflink
+ * adjustments.
+ */
+ if (xfs_is_reflink_inode(ip) && whichfork == XFS_DATA_FORK)
+ max_len = min(len, xfs_refcount_max_unmap(tp->t_log_res));
+ else
+ max_len = len;
+
if (!(ifp->if_flags & XFS_IFEXTENTS) &&
(error = xfs_iread_extents(tp, ip, whichfork)))
return error;
@@ -5499,7 +5510,7 @@ __xfs_bunmapi(
extno = 0;
while (bno != (xfs_fileoff_t)-1 && bno >= start && lastx >= 0 &&
- (nexts == 0 || extno < nexts)) {
+ (nexts == 0 || extno < nexts) && max_len > 0) {
/*
* Is the found extent after a hole in which bno lives?
* Just back up to the previous extent, if so.
@@ -5531,6 +5542,15 @@ __xfs_bunmapi(
}
if (del.br_startoff + del.br_blockcount > bno + 1)
del.br_blockcount = bno + 1 - del.br_startoff;
+
+ /* How much can we safely unmap? */
+ if (max_len < del.br_blockcount) {
+ del.br_startoff += del.br_blockcount - max_len;
+ if (!wasdel)
+ del.br_startblock += del.br_blockcount - max_len;
+ del.br_blockcount = max_len;
+ }
+
sum = del.br_startblock + del.br_blockcount;
if (isrt &&
(mod = do_mod(sum, mp->m_sb.sb_rextsize))) {
@@ -5707,6 +5727,7 @@ __xfs_bunmapi(
if (!isrt && wasdel)
xfs_mod_fdblocks(mp, (int64_t)del.br_blockcount, false);
+ max_len -= del.br_blockcount;
bno = del.br_startoff - 1;
nodelete:
/*
@@ -6472,15 +6493,16 @@ xfs_bmap_finish_one(
int whichfork,
xfs_fileoff_t startoff,
xfs_fsblock_t startblock,
- xfs_filblks_t blockcount,
+ xfs_filblks_t *blockcount,
xfs_exntst_t state)
{
- int error = 0, done;
+ xfs_fsblock_t firstfsb;
+ int error = 0;
trace_xfs_bmap_deferred(tp->t_mountp,
XFS_FSB_TO_AGNO(tp->t_mountp, startblock), type,
XFS_FSB_TO_AGBNO(tp->t_mountp, startblock),
- ip->i_ino, whichfork, startoff, blockcount, state);
+ ip->i_ino, whichfork, startoff, *blockcount, state);
if (WARN_ON_ONCE(whichfork != XFS_DATA_FORK))
return -EFSCORRUPTED;
@@ -6492,13 +6514,13 @@ xfs_bmap_finish_one(
switch (type) {
case XFS_BMAP_MAP:
- error = xfs_bmapi_remap(tp, ip, startoff, blockcount,
+ error = xfs_bmapi_remap(tp, ip, startoff, *blockcount,
startblock, dfops);
+ *blockcount = 0;
break;
case XFS_BMAP_UNMAP:
- error = xfs_bunmapi(tp, ip, startoff, blockcount,
- XFS_BMAPI_REMAP, 1, &startblock, dfops, &done);
- ASSERT(done);
+ error = __xfs_bunmapi(tp, ip, startoff, blockcount,
+ XFS_BMAPI_REMAP, 1, &firstfsb, dfops);
break;
default:
ASSERT(0);