drbd: split drbd_al_begin_io into fastpath, prepare, and commit

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 72 insertions, 33 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 1d7244d2a910..e4f1231c2ef2 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -104,7 +104,6 @@ struct update_al_work {
         int err;
 };
 
-static int al_write_transaction(struct drbd_conf *mdev, bool delegate);
 
 void *drbd_md_get_buffer(struct drbd_conf *mdev)
 {
@@ -246,30 +245,37 @@ static struct lc_element *_al_get(struct drbd_conf *mdev, unsigned int enr)
         return al_ext;
 }
 
-/*
- * @delegate:   delegate activity log I/O to the worker thread
- */
-void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool delegate)
+bool drbd_al_begin_io_fastpath(struct drbd_conf *mdev, struct drbd_interval *i)
 {
         /* for bios crossing activity log extent boundaries,
          * we may need to activate two extents in one go */
         unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
         unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
-        unsigned enr;
-        bool need_transaction = false;
-        bool locked = false;
+        bool fastpath_ok = true;
 
-        /* When called through generic_make_request(), we must delegate
-         * activity log I/O to the worker thread: a further request
-         * submitted via generic_make_request() within the same task
-         * would be queued on current->bio_list, and would only start
-         * after this function returns (see generic_make_request()).
-         *
-         * However, if we *are* the worker, we must not delegate to ourselves.
-         */
+        D_ASSERT((unsigned)(last - first) <= 1);
+        D_ASSERT(atomic_read(&mdev->local_cnt) > 0);
+
+        /* FIXME figure out a fast path for bios crossing AL extent boundaries */
+        if (first != last)
+                return false;
+
+        spin_lock_irq(&mdev->al_lock);
+        fastpath_ok =
+                lc_find(mdev->resync, first/AL_EXT_PER_BM_SECT) == NULL &&
+                lc_try_get(mdev->act_log, first) != NULL;
+        spin_unlock_irq(&mdev->al_lock);
+        return fastpath_ok;
+}
 
-        if (delegate)
-                BUG_ON(current == mdev->tconn->worker.task);
+bool drbd_al_begin_io_prepare(struct drbd_conf *mdev, struct drbd_interval *i)
+{
+        /* for bios crossing activity log extent boundaries,
+         * we may need to activate two extents in one go */
+        unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
+        unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
+        unsigned enr;
+        bool need_transaction = false;
 
         D_ASSERT(first <= last);
         D_ASSERT(atomic_read(&mdev->local_cnt) > 0);
@@ -280,11 +286,28 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool dele
                 if (al_ext->lc_number != enr)
                         need_transaction = true;
         }
+        return need_transaction;
+}
 
-        /* If *this* request was to an already active extent,
-         * we're done, even if there are pending changes. */
-        if (!need_transaction)
-                return;
+static int al_write_transaction(struct drbd_conf *mdev, bool delegate);
+
+/* When called through generic_make_request(), we must delegate
+ * activity log I/O to the worker thread: a further request
+ * submitted via generic_make_request() within the same task
+ * would be queued on current->bio_list, and would only start
+ * after this function returns (see generic_make_request()).
+ *
+ * However, if we *are* the worker, we must not delegate to ourselves.
+ */
+
+/*
+ * @delegate:   delegate activity log I/O to the worker thread
+ */
+void drbd_al_begin_io_commit(struct drbd_conf *mdev, bool delegate)
+{
+        bool locked = false;
+
+        BUG_ON(delegate && current == mdev->tconn->worker.task);
 
         /* Serialize multiple transactions.
          * This uses test_and_set_bit, memory barrier is implicit.
@@ -303,11 +326,8 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool dele
                         write_al_updates = rcu_dereference(mdev->ldev->disk_conf)->al_updates;
                         rcu_read_unlock();
 
-                        if (write_al_updates) {
+                        if (write_al_updates)
                                 al_write_transaction(mdev, delegate);
-                                mdev->al_writ_cnt++;
-                        }
-
                         spin_lock_irq(&mdev->al_lock);
                         /* FIXME
                         if (err)
@@ -321,6 +341,17 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool dele
         }
 }
 
+/*
+ * @delegate:   delegate activity log I/O to the worker thread
+ */
+void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool delegate)
+{
+        BUG_ON(delegate && current == mdev->tconn->worker.task);
+
+        if (drbd_al_begin_io_prepare(mdev, i))
+                drbd_al_begin_io_commit(mdev, delegate);
+}
+
 void drbd_al_complete_io(struct drbd_conf *mdev, struct drbd_interval *i)
 {
         /* for bios crossing activity log extent boundaries,
@@ -478,15 +509,22 @@ _al_write_transaction(struct drbd_conf *mdev)
         crc = crc32c(0, buffer, 4096);
         buffer->crc32c = cpu_to_be32(crc);
 
-        /* normal execution path goes through all three branches */
         if (drbd_bm_write_hinted(mdev))
                 err = -EIO;
-                /* drbd_chk_io_error done already */
-        else if (drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
-                err = -EIO;
-                drbd_chk_io_error(mdev, 1, DRBD_META_IO_ERROR);
-        } else {
-                mdev->al_tr_number++;
+        else {
+                bool write_al_updates;
+                rcu_read_lock();
+                write_al_updates = rcu_dereference(mdev->ldev->disk_conf)->al_updates;
+                rcu_read_unlock();
+                if (write_al_updates) {
+                        if (drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
+                                err = -EIO;
+                                drbd_chk_io_error(mdev, 1, DRBD_META_IO_ERROR);
+                        } else {
+                                mdev->al_tr_number++;
+                                mdev->al_writ_cnt++;
+                        }
+                }
         }
 
         drbd_md_put_buffer(mdev);
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index a6b71b6076b5..b7b52dd42325 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1611,6 +1611,7 @@ extern const char *drbd_conn_str(enum drbd_conns s);
 extern const char *drbd_role_str(enum drbd_role s);
 
 /* drbd_actlog.c */
+extern bool drbd_al_begin_io_fastpath(struct drbd_conf *mdev, struct drbd_interval *i);
 extern void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool delegate);
 extern void drbd_al_complete_io(struct drbd_conf *mdev, struct drbd_interval *i);
 extern void drbd_rs_complete_io(struct drbd_conf *mdev, sector_t sector);