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authorDave Chinner <dchinner@redhat.com>2019-09-05 17:32:48 -0700
committerDarrick J. Wong <darrick.wong@oracle.com>2019-09-05 21:36:12 -0700
commit7c107afb871a031cdec93e274486ae1dbe8d8f17 (patch)
tree3f4fce045cd32f5c704572ed2a15a6b8792290d8 /fs/xfs
parenteb2e99943c5bd528af67516fbd9db0ad15e61611 (diff)
downloadlinux-7c107afb871a031cdec93e274486ae1dbe8d8f17.tar.bz2
xfs: push the AIL in xlog_grant_head_wake
In the situation where the log is full and the CIL has not recently flushed, the AIL push threshold is throttled back to the where the last write of the head of the log was completed. This is stored in log->l_last_sync_lsn. Hence if the CIL holds > 25% of the log space pinned by flushes and/or aggregation in progress, we can get the situation where the head of the log lags a long way behind the reservation grant head. When this happens, the AIL push target is trimmed back from where the reservation grant head wants to push the log tail to, back to where the head of the log currently is. This means the push target doesn't reach far enough into the log to actually move the tail before the transaction reservation goes to sleep. When the CIL push completes, it moves the log head forward such that the AIL push target can now be moved, but that has no mechanism for puhsing the log tail. Further, if the next tail movement of the log is not large enough wake the waiter (i.e. still not enough space for it to have a reservation granted), we don't wake anything up, and hence we do not update the AIL push target to take into account the head of the log moving and allowing the push target to be moved forwards. To avoid this particular condition, if we fail to wake the first waiter on the grant head because we don't have enough space, push on the AIL again. This will pick up any movement of the log head and allow the push target to move forward due to completion of CIL pushing. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs')
-rw-r--r--fs/xfs/xfs_log.c29
1 files changed, 28 insertions, 1 deletions
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 3e0a105b6cc9..4dbe063217ac 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -214,15 +214,42 @@ xlog_grant_head_wake(
{
struct xlog_ticket *tic;
int need_bytes;
+ bool woken_task = false;
list_for_each_entry(tic, &head->waiters, t_queue) {
+
+ /*
+ * There is a chance that the size of the CIL checkpoints in
+ * progress at the last AIL push target calculation resulted in
+ * limiting the target to the log head (l_last_sync_lsn) at the
+ * time. This may not reflect where the log head is now as the
+ * CIL checkpoints may have completed.
+ *
+ * Hence when we are woken here, it may be that the head of the
+ * log that has moved rather than the tail. As the tail didn't
+ * move, there still won't be space available for the
+ * reservation we require. However, if the AIL has already
+ * pushed to the target defined by the old log head location, we
+ * will hang here waiting for something else to update the AIL
+ * push target.
+ *
+ * Therefore, if there isn't space to wake the first waiter on
+ * the grant head, we need to push the AIL again to ensure the
+ * target reflects both the current log tail and log head
+ * position before we wait for the tail to move again.
+ */
+
need_bytes = xlog_ticket_reservation(log, head, tic);
- if (*free_bytes < need_bytes)
+ if (*free_bytes < need_bytes) {
+ if (!woken_task)
+ xlog_grant_push_ail(log, need_bytes);
return false;
+ }
*free_bytes -= need_bytes;
trace_xfs_log_grant_wake_up(log, tic);
wake_up_process(tic->t_task);
+ woken_task = true;
}
return true;