return (bp->b_page_count * PAGE_SIZE) - bp->b_offset;
}
+/*
+ * Bump the I/O in flight count on the buftarg if we haven't yet done so for
+ * this buffer. The count is incremented once per buffer (per hold cycle)
+ * because the corresponding decrement is deferred to buffer release. Buffers
+ * can undergo I/O multiple times in a hold-release cycle and per buffer I/O
+ * tracking adds unnecessary overhead. This is used for sychronization purposes
+ * with unmount (see xfs_wait_buftarg()), so all we really need is a count of
+ * in-flight buffers.
+ *
+ * Buffers that are never released (e.g., superblock, iclog buffers) must set
+ * the XBF_NO_IOACCT flag before I/O submission. Otherwise, the buftarg count
+ * never reaches zero and unmount hangs indefinitely.
+ */
+static inline void
+xfs_buf_ioacct_inc(
+ struct xfs_buf *bp)
+{
+ if (bp->b_flags & (XBF_NO_IOACCT|_XBF_IN_FLIGHT))
+ return;
+
+ ASSERT(bp->b_flags & XBF_ASYNC);
+ bp->b_flags |= _XBF_IN_FLIGHT;
+ percpu_counter_inc(&bp->b_target->bt_io_count);
+}
+
+/*
+ * Clear the in-flight state on a buffer about to be released to the LRU or
+ * freed and unaccount from the buftarg.
+ */
+static inline void
+xfs_buf_ioacct_dec(
+ struct xfs_buf *bp)
+{
+ if (!(bp->b_flags & _XBF_IN_FLIGHT))
+ return;
+
+ ASSERT(bp->b_flags & XBF_ASYNC);
+ bp->b_flags &= ~_XBF_IN_FLIGHT;
+ percpu_counter_dec(&bp->b_target->bt_io_count);
+}
+
/*
* When we mark a buffer stale, we remove the buffer from the LRU and clear the
* b_lru_ref count so that the buffer is freed immediately when the buffer
*/
bp->b_flags &= ~_XBF_DELWRI_Q;
+ /*
+ * Once the buffer is marked stale and unlocked, a subsequent lookup
+ * could reset b_flags. There is no guarantee that the buffer is
+ * unaccounted (released to LRU) before that occurs. Drop in-flight
+ * status now to preserve accounting consistency.
+ */
+ xfs_buf_ioacct_dec(bp);
+
spin_lock(&bp->b_lock);
atomic_set(&bp->b_lru_ref, 0);
if (!(bp->b_state & XFS_BSTATE_DISPOSE) &&
struct xfs_buf *bp;
DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
- bp = _xfs_buf_alloc(target, &map, 1, 0);
+ /* flags might contain irrelevant bits, pass only what we care about */
+ bp = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT);
if (unlikely(bp == NULL))
goto fail;
}
/*
- * Releases a hold on the specified buffer. If the
- * the hold count is 1, calls xfs_buf_free.
+ * Release a hold on the specified buffer. If the hold count is 1, the buffer is
+ * placed on LRU or freed (depending on b_lru_ref).
*/
void
xfs_buf_rele(
xfs_buf_t *bp)
{
struct xfs_perag *pag = bp->b_pag;
+ bool release;
+ bool freebuf = false;
trace_xfs_buf_rele(bp, _RET_IP_);
if (!pag) {
ASSERT(list_empty(&bp->b_lru));
ASSERT(RB_EMPTY_NODE(&bp->b_rbnode));
- if (atomic_dec_and_test(&bp->b_hold))
+ if (atomic_dec_and_test(&bp->b_hold)) {
+ xfs_buf_ioacct_dec(bp);
xfs_buf_free(bp);
+ }
return;
}
ASSERT(!RB_EMPTY_NODE(&bp->b_rbnode));
ASSERT(atomic_read(&bp->b_hold) > 0);
- if (atomic_dec_and_lock(&bp->b_hold, &pag->pag_buf_lock)) {
- spin_lock(&bp->b_lock);
- if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) {
- /*
- * If the buffer is added to the LRU take a new
- * reference to the buffer for the LRU and clear the
- * (now stale) dispose list state flag
- */
- if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) {
- bp->b_state &= ~XFS_BSTATE_DISPOSE;
- atomic_inc(&bp->b_hold);
- }
- spin_unlock(&bp->b_lock);
- spin_unlock(&pag->pag_buf_lock);
- } else {
- /*
- * most of the time buffers will already be removed from
- * the LRU, so optimise that case by checking for the
- * XFS_BSTATE_DISPOSE flag indicating the last list the
- * buffer was on was the disposal list
- */
- if (!(bp->b_state & XFS_BSTATE_DISPOSE)) {
- list_lru_del(&bp->b_target->bt_lru, &bp->b_lru);
- } else {
- ASSERT(list_empty(&bp->b_lru));
- }
- spin_unlock(&bp->b_lock);
- ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
- rb_erase(&bp->b_rbnode, &pag->pag_buf_tree);
- spin_unlock(&pag->pag_buf_lock);
- xfs_perag_put(pag);
- xfs_buf_free(bp);
+ release = atomic_dec_and_lock(&bp->b_hold, &pag->pag_buf_lock);
+ spin_lock(&bp->b_lock);
+ if (!release) {
+ /*
+ * Drop the in-flight state if the buffer is already on the LRU
+ * and it holds the only reference. This is racy because we
+ * haven't acquired the pag lock, but the use of _XBF_IN_FLIGHT
+ * ensures the decrement occurs only once per-buf.
+ */
+ if ((atomic_read(&bp->b_hold) == 1) && !list_empty(&bp->b_lru))
+ xfs_buf_ioacct_dec(bp);
+ goto out_unlock;
+ }
+
+ /* the last reference has been dropped ... */
+ xfs_buf_ioacct_dec(bp);
+ if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) {
+ /*
+ * If the buffer is added to the LRU take a new reference to the
+ * buffer for the LRU and clear the (now stale) dispose list
+ * state flag
+ */
+ if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) {
+ bp->b_state &= ~XFS_BSTATE_DISPOSE;
+ atomic_inc(&bp->b_hold);
+ }
+ spin_unlock(&pag->pag_buf_lock);
+ } else {
+ /*
+ * most of the time buffers will already be removed from the
+ * LRU, so optimise that case by checking for the
+ * XFS_BSTATE_DISPOSE flag indicating the last list the buffer
+ * was on was the disposal list
+ */
+ if (!(bp->b_state & XFS_BSTATE_DISPOSE)) {
+ list_lru_del(&bp->b_target->bt_lru, &bp->b_lru);
+ } else {
+ ASSERT(list_empty(&bp->b_lru));
}
+
+ ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+ rb_erase(&bp->b_rbnode, &pag->pag_buf_tree);
+ spin_unlock(&pag->pag_buf_lock);
+ xfs_perag_put(pag);
+ freebuf = true;
}
+
+out_unlock:
+ spin_unlock(&bp->b_lock);
+
+ if (freebuf)
+ xfs_buf_free(bp);
}
int locked;
locked = down_trylock(&bp->b_sema) == 0;
- if (locked)
+ if (locked) {
XB_SET_OWNER(bp);
-
- trace_xfs_buf_trylock(bp, _RET_IP_);
+ trace_xfs_buf_trylock(bp, _RET_IP_);
+ } else {
+ trace_xfs_buf_trylock_fail(bp, _RET_IP_);
+ }
return locked;
}
* xfs_buf_ioend too early.
*/
atomic_set(&bp->b_io_remaining, 1);
+ xfs_buf_ioacct_inc(bp);
_xfs_buf_ioapply(bp);
/*
int loop = 0;
/*
- * We need to flush the buffer workqueue to ensure that all IO
- * completion processing is 100% done. Just waiting on buffer locks is
- * not sufficient for async IO as the reference count held over IO is
- * not released until after the buffer lock is dropped. Hence we need to
- * ensure here that all reference counts have been dropped before we
- * start walking the LRU list.
+ * First wait on the buftarg I/O count for all in-flight buffers to be
+ * released. This is critical as new buffers do not make the LRU until
+ * they are released.
+ *
+ * Next, flush the buffer workqueue to ensure all completion processing
+ * has finished. Just waiting on buffer locks is not sufficient for
+ * async IO as the reference count held over IO is not released until
+ * after the buffer lock is dropped. Hence we need to ensure here that
+ * all reference counts have been dropped before we start walking the
+ * LRU list.
*/
+ while (percpu_counter_sum(&btp->bt_io_count))
+ delay(100);
drain_workqueue(btp->bt_mount->m_buf_workqueue);
/* loop until there is nothing left on the lru list. */
struct xfs_buftarg *btp)
{
unregister_shrinker(&btp->bt_shrinker);
+ ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
+ percpu_counter_destroy(&btp->bt_io_count);
list_lru_destroy(&btp->bt_lru);
if (mp->m_flags & XFS_MOUNT_BARRIER)
if (list_lru_init(&btp->bt_lru))
goto error;
+ if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
+ goto error;
+
btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
btp->bt_shrinker.seeks = DEFAULT_SEEKS;
return 0;
}
+/*
+ * submit buffers for write.
+ *
+ * When we have a large buffer list, we do not want to hold all the buffers
+ * locked while we block on the request queue waiting for IO dispatch. To avoid
+ * this problem, we lock and submit buffers in groups of 50, thereby minimising
+ * the lock hold times for lists which may contain thousands of objects.
+ *
+ * To do this, we sort the buffer list before we walk the list to lock and
+ * submit buffers, and we plug and unplug around each group of buffers we
+ * submit.
+ */
static int
-__xfs_buf_delwri_submit(
+xfs_buf_delwri_submit_buffers(
struct list_head *buffer_list,
- struct list_head *io_list,
- bool wait)
+ struct list_head *wait_list)
{
- struct blk_plug plug;
struct xfs_buf *bp, *n;
+ LIST_HEAD (submit_list);
int pinned = 0;
+ struct blk_plug plug;
+ list_sort(NULL, buffer_list, xfs_buf_cmp);
+
+ blk_start_plug(&plug);
list_for_each_entry_safe(bp, n, buffer_list, b_list) {
- if (!wait) {
+ if (!wait_list) {
if (xfs_buf_ispinned(bp)) {
pinned++;
continue;
continue;
}
- list_move_tail(&bp->b_list, io_list);
trace_xfs_buf_delwri_split(bp, _RET_IP_);
- }
-
- list_sort(NULL, io_list, xfs_buf_cmp);
-
- blk_start_plug(&plug);
- list_for_each_entry_safe(bp, n, io_list, b_list) {
- bp->b_flags &= ~(_XBF_DELWRI_Q | XBF_ASYNC | XBF_WRITE_FAIL);
- bp->b_flags |= XBF_WRITE | XBF_ASYNC;
/*
- * we do all Io submission async. This means if we need to wait
- * for IO completion we need to take an extra reference so the
- * buffer is still valid on the other side.
+ * We do all IO submission async. This means if we need
+ * to wait for IO completion we need to take an extra
+ * reference so the buffer is still valid on the other
+ * side. We need to move the buffer onto the io_list
+ * at this point so the caller can still access it.
*/
- if (wait)
+ bp->b_flags &= ~(_XBF_DELWRI_Q | XBF_WRITE_FAIL);
+ bp->b_flags |= XBF_WRITE | XBF_ASYNC;
+ if (wait_list) {
xfs_buf_hold(bp);
- else
+ list_move_tail(&bp->b_list, wait_list);
+ } else
list_del_init(&bp->b_list);
xfs_buf_submit(bp);
xfs_buf_delwri_submit_nowait(
struct list_head *buffer_list)
{
- LIST_HEAD (io_list);
- return __xfs_buf_delwri_submit(buffer_list, &io_list, false);
+ return xfs_buf_delwri_submit_buffers(buffer_list, NULL);
}
/*
xfs_buf_delwri_submit(
struct list_head *buffer_list)
{
- LIST_HEAD (io_list);
+ LIST_HEAD (wait_list);
int error = 0, error2;
struct xfs_buf *bp;
- __xfs_buf_delwri_submit(buffer_list, &io_list, true);
+ xfs_buf_delwri_submit_buffers(buffer_list, &wait_list);
/* Wait for IO to complete. */
- while (!list_empty(&io_list)) {
- bp = list_first_entry(&io_list, struct xfs_buf, b_list);
+ while (!list_empty(&wait_list)) {
+ bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
list_del_init(&bp->b_list);
git.samba.org / sfrench / cifs-2.6.git / blobdiff