GFS2: Various gfs2_logd improvements

This patch contains various tweaks to how log flushes and active item writeback
work. gfs2_logd is now managed by a waitqueue, and gfs2_log_reseve now waits
for gfs2_logd to do the log flushing.  Multiple functions were rewritten to
remove the need to call gfs2_log_lock(). Instead of using one test to see if
gfs2_logd had work to do, there are now seperate tests to check if there
are two many buffers in the incore log or if there are two many items on the
active items list.

This patch is a port of a patch Steve Whitehouse wrote about a year ago, with
some minor changes.  Since gfs2_ail1_start always submits all the active items,
it no longer needs to keep track of the first ai submitted, so this has been
removed. In gfs2_log_reserve(), the order of the calls to
prepare_to_wait_exclusive() and wake_up() when firing off the logd thread has
been switched.  If it called wake_up first there was a small window for a race,
where logd could run and return before gfs2_log_reserve was ready to get woken
up. If gfs2_logd ran, but did not free up enough blocks, gfs2_log_reserve()
would be left waiting for gfs2_logd to eventualy run because it timed out.
Finally, gt_logd_secs, which controls how long to wait before gfs2_logd times
out, and flushes the log, can now be set on mount with ar_commit.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

9 files changed, 126 insertions, 92 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 3aac46f6853e..08dd65745473 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -439,9 +439,6 @@ struct gfs2_args {
 struct gfs2_tune {
         spinlock_t gt_spin;
 
-        unsigned int gt_incore_log_blocks;
-        unsigned int gt_log_flush_secs;
-
         unsigned int gt_logd_secs;
 
         unsigned int gt_quota_simul_sync; /* Max quotavals to sync at once */
@@ -618,6 +615,7 @@ struct gfs2_sbd {
         unsigned int sd_log_commited_databuf;
         int sd_log_commited_revoke;
 
+        atomic_t sd_log_pinned;
         unsigned int sd_log_num_buf;
         unsigned int sd_log_num_revoke;
         unsigned int sd_log_num_rg;
@@ -629,15 +627,17 @@ struct gfs2_sbd {
         struct list_head sd_log_le_databuf;
         struct list_head sd_log_le_ordered;
 
+        atomic_t sd_log_thresh1;
+        atomic_t sd_log_thresh2;
         atomic_t sd_log_blks_free;
-        struct mutex sd_log_reserve_mutex;
+        wait_queue_head_t sd_log_waitq;
+        wait_queue_head_t sd_logd_waitq;
 
         u64 sd_log_sequence;
         unsigned int sd_log_head;
         unsigned int sd_log_tail;
         int sd_log_idle;
 
-        unsigned long sd_log_flush_time;
         struct rw_semaphore sd_log_flush_lock;
         atomic_t sd_log_in_flight;
         wait_queue_head_t sd_log_flush_wait;
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index e5bf4b59d46e..d5959df6deb2 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -168,12 +168,11 @@ static int gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_ail *ai, int fl
         return list_empty(&ai->ai_ail1_list);
 }
 
-static void gfs2_ail1_start(struct gfs2_sbd *sdp, int flags)
+static void gfs2_ail1_start(struct gfs2_sbd *sdp)
 {
         struct list_head *head;
         u64 sync_gen;
-        struct list_head *first;
-        struct gfs2_ail *first_ai, *ai, *tmp;
+        struct gfs2_ail *ai;
         int done = 0;
 
         gfs2_log_lock(sdp);
@@ -184,21 +183,9 @@ static void gfs2_ail1_start(struct gfs2_sbd *sdp, int flags)
         }
         sync_gen = sdp->sd_ail_sync_gen++;
 
-        first = head->prev;
-        first_ai = list_entry(first, struct gfs2_ail, ai_list);
-        first_ai->ai_sync_gen = sync_gen;
-        gfs2_ail1_start_one(sdp, first_ai); /* This may drop log lock */
-
-        if (flags & DIO_ALL)
-                first = NULL;
-
         while(!done) {
-                if (first && (head->prev != first ||
-                              gfs2_ail1_empty_one(sdp, first_ai, 0)))
-                        break;
-
                 done = 1;
-                list_for_each_entry_safe_reverse(ai, tmp, head, ai_list) {
+                list_for_each_entry_reverse(ai, head, ai_list) {
                         if (ai->ai_sync_gen >= sync_gen)
                                 continue;
                         ai->ai_sync_gen = sync_gen;
@@ -290,58 +277,57 @@ static void ail2_empty(struct gfs2_sbd *sdp, unsigned int new_tail)
  * flush time, so we ensure that we have just enough free blocks at all
  * times to avoid running out during a log flush.
  *
+ * We no longer flush the log here, instead we wake up logd to do that
+ * for us. To avoid the thundering herd and to ensure that we deal fairly
+ * with queued waiters, we use an exclusive wait. This means that when we
+ * get woken with enough journal space to get our reservation, we need to
+ * wake the next waiter on the list.
+ *
  * Returns: errno
  */
 
 int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks)
 {
-        unsigned int try = 0;
         unsigned reserved_blks = 6 * (4096 / sdp->sd_vfs->s_blocksize);
+        unsigned wanted = blks + reserved_blks;
+        DEFINE_WAIT(wait);
+        int did_wait = 0;
+        unsigned int free_blocks;
 
         if (gfs2_assert_warn(sdp, blks) ||
             gfs2_assert_warn(sdp, blks <= sdp->sd_jdesc->jd_blocks))
                 return -EINVAL;
-
-        mutex_lock(&sdp->sd_log_reserve_mutex);
-        gfs2_log_lock(sdp);
-        while(atomic_read(&sdp->sd_log_blks_free) <= (blks + reserved_blks)) {
-                gfs2_log_unlock(sdp);
-                gfs2_ail1_empty(sdp, 0);
-                gfs2_log_flush(sdp, NULL);
-
-                if (try++)
-                        gfs2_ail1_start(sdp, 0);
-                gfs2_log_lock(sdp);
+retry:
+        free_blocks = atomic_read(&sdp->sd_log_blks_free);
+        if (unlikely(free_blocks <= wanted)) {
+                do {
+                        prepare_to_wait_exclusive(&sdp->sd_log_waitq, &wait,
+                                        TASK_UNINTERRUPTIBLE);
+                        wake_up(&sdp->sd_logd_waitq);
+                        did_wait = 1;
+                        if (atomic_read(&sdp->sd_log_blks_free) <= wanted)
+                                io_schedule();
+                        free_blocks = atomic_read(&sdp->sd_log_blks_free);
+                } while(free_blocks <= wanted);
+                finish_wait(&sdp->sd_log_waitq, &wait);
         }
-        atomic_sub(blks, &sdp->sd_log_blks_free);
+        if (atomic_cmpxchg(&sdp->sd_log_blks_free, free_blocks,
+                                free_blocks - blks) != free_blocks)
+                goto retry;
         trace_gfs2_log_blocks(sdp, -blks);
-        gfs2_log_unlock(sdp);
-        mutex_unlock(&sdp->sd_log_reserve_mutex);
+
+        /*
+         * If we waited, then so might others, wake them up _after_ we get
+         * our share of the log.
+         */
+        if (unlikely(did_wait))
+                wake_up(&sdp->sd_log_waitq);
 
         down_read(&sdp->sd_log_flush_lock);
 
         return 0;
 }
 
-/**
- * gfs2_log_release - Release a given number of log blocks
- * @sdp: The GFS2 superblock
- * @blks: The number of blocks
- *
- */
-
-void gfs2_log_release(struct gfs2_sbd *sdp, unsigned int blks)
-{
-
-        gfs2_log_lock(sdp);
-        atomic_add(blks, &sdp->sd_log_blks_free);
-        trace_gfs2_log_blocks(sdp, blks);
-        gfs2_assert_withdraw(sdp,
-                             atomic_read(&sdp->sd_log_blks_free) <= sdp->sd_jdesc->jd_blocks);
-        gfs2_log_unlock(sdp);
-        up_read(&sdp->sd_log_flush_lock);