/*
* xfs_trans_push_ail
*
* This routine is called to move the tail of the AIL
* forward. It does this by trying to flush items in the AIL
* whose lsns are below the given threshold_lsn.
*
* The routine returns the lsn of the tail of the log.
*/
xfs_lsn_t
xfs_trans_push_ail(
xfs_mount_t *mp,
xfs_lsn_t threshold_lsn)
{
xfs_lsn_t lsn;
xfs_log_item_t *lip;
int gen;
int restarts;
int lock_result;
int flush_log;
SPLDECL(s);
#define XFS_TRANS_PUSH_AIL_RESTARTS 10
AIL_LOCK(mp,s);
lip = xfs_trans_first_ail(mp, &gen);
if (lip == NULL || XFS_FORCED_SHUTDOWN(mp)) {
/*
* Just return if the AIL is empty.
*/
AIL_UNLOCK(mp, s);
return (xfs_lsn_t)0;
}
XFS_STATS_INC(xs_push_ail);
/*
* While the item we are looking at is below the given threshold
* try to flush it out. Make sure to limit the number of times
* we allow xfs_trans_next_ail() to restart scanning from the
* beginning of the list. We'd like not to stop until we've at least
* tried to push on everything in the AIL with an LSN less than
* the given threshold. However, we may give up before that if
* we realize that we've been holding the AIL_LOCK for 'too long',
* blocking interrupts. Currently, too long is < 500us roughly.
*/
flush_log = 0;
restarts = 0;
while (((restarts < XFS_TRANS_PUSH_AIL_RESTARTS) &&
(XFS_LSN_CMP(lip->li_lsn, threshold_lsn) < 0))) {
/*
* If we can lock the item without sleeping, unlock
* the AIL lock and flush the item. Then re-grab the
* AIL lock so we can look for the next item on the
* AIL. Since we unlock the AIL while we flush the
* item, the next routine may start over again at the
* the beginning of the list if anything has changed.
* That is what the generation count is for.
*
* If we can't lock the item, either its holder will flush
* it or it is already being flushed or it is being relogged.
* In any of these case it is being taken care of and we
* can just skip to the next item in the list.
*/
lock_result = IOP_TRYLOCK(lip);
switch (lock_result) {
case XFS_ITEM_SUCCESS:
AIL_UNLOCK(mp, s);
XFS_STATS_INC(xs_push_ail_success);
IOP_PUSH(lip);
AIL_LOCK(mp,s);
break;
case XFS_ITEM_PUSHBUF:
AIL_UNLOCK(mp, s);
XFS_STATS_INC(xs_push_ail_pushbuf);
#ifdef XFSRACEDEBUG
delay_for_intr();
delay(300);
#endif
ASSERT(lip->li_ops->iop_pushbuf);
ASSERT(lip);
IOP_PUSHBUF(lip);
AIL_LOCK(mp,s);
break;
case XFS_ITEM_PINNED:
XFS_STATS_INC(xs_push_ail_pinned);
flush_log = 1;
break;
case XFS_ITEM_LOCKED:
XFS_STATS_INC(xs_push_ail_locked);
break;
case XFS_ITEM_FLUSHING:
XFS_STATS_INC(xs_push_ail_flushing);
break;
default:
ASSERT(0);
break;
}
lip = xfs_trans_next_ail(mp, lip, &gen, &restarts);
if (lip == NULL) {
break;
}
if (XFS_FORCED_SHUTDOWN(mp)) {
/*
* Just return if we shut down during the last try.
*/
AIL_UNLOCK(mp, s);
return (xfs_lsn_t)0;
}
}
if (flush_log) {
/*
* If something we need to push out was pinned, then
* push out the log so it will become unpinned and
* move forward in the AIL.
*/
AIL_UNLOCK(mp, s);
XFS_STATS_INC(xs_push_ail_flush);
xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
AIL_LOCK(mp, s);
}
lip = xfs_ail_min(&(mp->m_ail));
if (lip == NULL) {
lsn = (xfs_lsn_t)0;
} else {
lsn = lip->li_lsn;
}
AIL_UNLOCK(mp, s);
return lsn;
} /* xfs_trans_push_ail */
/*
* Function that does the work of pushing on the AIL
*/
long
xfsaild_push(
xfs_mount_t *mp,
xfs_lsn_t *last_lsn)
{
long tout = 1000; /* milliseconds */
xfs_lsn_t last_pushed_lsn = *last_lsn;
xfs_lsn_t target = mp->m_ail.xa_target;
xfs_lsn_t lsn;
xfs_log_item_t *lip;
int gen;
int restarts;
int flush_log, count, stuck;
#define XFS_TRANS_PUSH_AIL_RESTARTS 10
spin_lock(&mp->m_ail_lock);
lip = xfs_trans_first_push_ail(mp, &gen, *last_lsn);
if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
/*
* AIL is empty or our push has reached the end.
*/
spin_unlock(&mp->m_ail_lock);
last_pushed_lsn = 0;
goto out;
}
XFS_STATS_INC(xs_push_ail);
/*
* While the item we are looking at is below the given threshold
* try to flush it out. We'd like not to stop until we've at least
* tried to push on everything in the AIL with an LSN less than
* the given threshold.
*
* However, we will stop after a certain number of pushes and wait
* for a reduced timeout to fire before pushing further. This
* prevents use from spinning when we can't do anything or there is
* lots of contention on the AIL lists.
*/
tout = 10;
lsn = lip->li_lsn;
flush_log = stuck = count = restarts = 0;
while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
int lock_result;
/*
* If we can lock the item without sleeping, unlock the AIL
* lock and flush the item. Then re-grab the AIL lock so we
* can look for the next item on the AIL. List changes are
* handled by the AIL lookup functions internally
*
* If we can't lock the item, either its holder will flush it
* or it is already being flushed or it is being relogged. In
* any of these case it is being taken care of and we can just
* skip to the next item in the list.
*/
lock_result = IOP_TRYLOCK(lip);
spin_unlock(&mp->m_ail_lock);
switch (lock_result) {
case XFS_ITEM_SUCCESS:
XFS_STATS_INC(xs_push_ail_success);
IOP_PUSH(lip);
last_pushed_lsn = lsn;
break;
case XFS_ITEM_PUSHBUF:
XFS_STATS_INC(xs_push_ail_pushbuf);
IOP_PUSHBUF(lip);
last_pushed_lsn = lsn;
break;
case XFS_ITEM_PINNED:
XFS_STATS_INC(xs_push_ail_pinned);
stuck++;
flush_log = 1;
break;
case XFS_ITEM_LOCKED:
XFS_STATS_INC(xs_push_ail_locked);
last_pushed_lsn = lsn;
stuck++;
break;
case XFS_ITEM_FLUSHING:
XFS_STATS_INC(xs_push_ail_flushing);
last_pushed_lsn = lsn;
stuck++;
break;
default:
ASSERT(0);
break;
}
spin_lock(&mp->m_ail_lock);
/* should we bother continuing? */
if (XFS_FORCED_SHUTDOWN(mp))
break;
ASSERT(mp->m_log);
count++;
/*
* Are there too many items we can't do anything with?
* If we we are skipping too many items because we can't flush
* them or they are already being flushed, we back off and
* given them time to complete whatever operation is being
* done. i.e. remove pressure from the AIL while we can't make
* progress so traversals don't slow down further inserts and
* removals to/from the AIL.
*
* The value of 100 is an arbitrary magic number based on
* observation.
*/
if (stuck > 100)
break;
lip = xfs_trans_next_ail(mp, lip, &gen, &restarts);
if (lip == NULL)
break;
if (restarts > XFS_TRANS_PUSH_AIL_RESTARTS)
break;
lsn = lip->li_lsn;
}
spin_unlock(&mp->m_ail_lock);
if (flush_log) {
/*
* If something we need to push out was pinned, then
* push out the log so it will become unpinned and
* move forward in the AIL.
*/
XFS_STATS_INC(xs_push_ail_flush);
xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
}
if (!count) {
/* We're past our target or empty, so idle */
tout = 1000;
} else if (XFS_LSN_CMP(lsn, target) >= 0) {
/*
* We reached the target so wait a bit longer for I/O to
* complete and remove pushed items from the AIL before we
* start the next scan from the start of the AIL.
*/
tout += 20;
last_pushed_lsn = 0;
} else if ((restarts > XFS_TRANS_PUSH_AIL_RESTARTS) ||
((stuck * 100) / count > 90)) {
/*
* Either there is a lot of contention on the AIL or we
* are stuck due to operations in progress. "Stuck" in this
* case is defined as >90% of the items we tried to push
* were stuck.
*
* Backoff a bit more to allow some I/O to complete before
* continuing from where we were.
*/
tout += 10;
}
out:
*last_lsn = last_pushed_lsn;
return tout;
} /* xfsaild_push */
