gfs2: Get rid of current_tail()

Keep the current value of the updated log tail in the super block as
sb_log_flush_tail instead of computing it on the fly.  This avoids
unnecessary sd_ail_lock taking and cleans up the code.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 8f8676c..51656b0 100644 (file)
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -838,8 +838,6 @@ struct gfs2_sbd {
        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;
 
        struct rw_semaphore sd_log_flush_lock;
@@ -849,6 +847,9 @@ struct gfs2_sbd {
        int sd_log_error; /* First log error */
        wait_queue_head_t sd_withdraw_wait;
 
+       unsigned int sd_log_tail;
+       unsigned int sd_log_flush_tail;
+       unsigned int sd_log_head;
        unsigned int sd_log_flush_head;
 
        spinlock_t sd_ail_lock;

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index ca9fa48..6b5584f 100644 (file)
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -242,6 +242,28 @@ static void gfs2_ail1_start(struct gfs2_sbd *sdp)
        return gfs2_ail1_flush(sdp, &wbc);
 }
 
+static void gfs2_log_update_flush_tail(struct gfs2_sbd *sdp)
+{
+       unsigned int new_flush_tail = sdp->sd_log_head;
+       struct gfs2_trans *tr;
+
+       if (!list_empty(&sdp->sd_ail1_list)) {
+               tr = list_last_entry(&sdp->sd_ail1_list,
+                                    struct gfs2_trans, tr_list);
+               new_flush_tail = tr->tr_first;
+       }
+       sdp->sd_log_flush_tail = new_flush_tail;
+}
+
+static void gfs2_log_update_head(struct gfs2_sbd *sdp)
+{
+       unsigned int new_head = sdp->sd_log_flush_head;
+
+       if (sdp->sd_log_flush_tail == sdp->sd_log_head)
+               sdp->sd_log_flush_tail = new_head;
+       sdp->sd_log_head = new_head;
+}
+
 /**
  * gfs2_ail1_empty_one - Check whether or not a trans in the AIL has been synced
  * @sdp: the filesystem
@@ -317,6 +339,7 @@ static int gfs2_ail1_empty(struct gfs2_sbd *sdp, int max_revokes)
                else
                        oldest_tr = 0;
        }
+       gfs2_log_update_flush_tail(sdp);
        ret = list_empty(&sdp->sd_ail1_list);
        spin_unlock(&sdp->sd_ail_lock);
 
@@ -544,30 +567,14 @@ static unsigned int calc_reserved(struct gfs2_sbd *sdp)
        return reserved;
 }
 
-static unsigned int current_tail(struct gfs2_sbd *sdp)
-{
-       struct gfs2_trans *tr;
-       unsigned int tail;
-
-       spin_lock(&sdp->sd_ail_lock);
-
-       if (list_empty(&sdp->sd_ail1_list)) {
-               tail = sdp->sd_log_head;
-       } else {
-               tr = list_last_entry(&sdp->sd_ail1_list, struct gfs2_trans,
-                               tr_list);
-               tail = tr->tr_first;
-       }
-
-       spin_unlock(&sdp->sd_ail_lock);
-
-       return tail;
-}
-
-static void log_pull_tail(struct gfs2_sbd *sdp, unsigned int new_tail)
+static void log_pull_tail(struct gfs2_sbd *sdp)
 {
-       unsigned int dist = log_distance(sdp, new_tail, sdp->sd_log_tail);
+       unsigned int new_tail = sdp->sd_log_flush_tail;
+       unsigned int dist;
 
+       if (new_tail == sdp->sd_log_tail)
+               return;
+       dist = log_distance(sdp, new_tail, sdp->sd_log_tail);
        ail2_empty(sdp, new_tail);
        gfs2_log_release(sdp, dist);
        sdp->sd_log_tail = new_tail;
@@ -822,26 +829,23 @@ void gfs2_write_log_header(struct gfs2_sbd *sdp, struct gfs2_jdesc *jd,
 
 static void log_write_header(struct gfs2_sbd *sdp, u32 flags)
 {
-       unsigned int tail;
        int op_flags = REQ_PREFLUSH | REQ_FUA | REQ_META | REQ_SYNC;
        enum gfs2_freeze_state state = atomic_read(&sdp->sd_freeze_state);
 
        gfs2_assert_withdraw(sdp, (state != SFS_FROZEN));
-       tail = current_tail(sdp);
 
        if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags)) {
                gfs2_ordered_wait(sdp);
                log_flush_wait(sdp);
                op_flags = REQ_SYNC | REQ_META | REQ_PRIO;
        }
-       sdp->sd_log_idle = (tail == sdp->sd_log_flush_head);
-       gfs2_write_log_header(sdp, sdp->sd_jdesc, sdp->sd_log_sequence++, tail,
-                             sdp->sd_log_flush_head, flags, op_flags);
+       sdp->sd_log_idle = (sdp->sd_log_flush_tail == sdp->sd_log_flush_head);
+       gfs2_write_log_header(sdp, sdp->sd_jdesc, sdp->sd_log_sequence++,
+                             sdp->sd_log_flush_tail, sdp->sd_log_flush_head,
+                             flags, op_flags);
        gfs2_log_incr_head(sdp);
        log_flush_wait(sdp);
-
-       if (sdp->sd_log_tail != tail)
-               log_pull_tail(sdp, tail);
+       log_pull_tail(sdp);
 }
 
 /**
@@ -991,7 +995,7 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
        if (sdp->sd_log_head != sdp->sd_log_flush_head) {
                log_flush_wait(sdp);
                log_write_header(sdp, flags);
-       } else if (sdp->sd_log_tail != current_tail(sdp) && !sdp->sd_log_idle) {
+       } else if (sdp->sd_log_tail != sdp->sd_log_flush_tail && !sdp->sd_log_idle) {
                atomic_dec(&sdp->sd_log_blks_free); /* Adjust for unreserved buffer */
                trace_gfs2_log_blocks(sdp, -1);
                log_write_header(sdp, flags);
@@ -1001,7 +1005,7 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
        lops_after_commit(sdp, tr);
 
        gfs2_log_lock(sdp);
-       sdp->sd_log_head = sdp->sd_log_flush_head;
+       gfs2_log_update_head(sdp);
        sdp->sd_log_blks_reserved = 0;
        sdp->sd_log_committed_revoke = 0;
 
@@ -1021,7 +1025,7 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
                        atomic_dec(&sdp->sd_log_blks_free); /* Adjust for unreserved buffer */
                        trace_gfs2_log_blocks(sdp, -1);
                        log_write_header(sdp, flags);
-                       sdp->sd_log_head = sdp->sd_log_flush_head;
+                       gfs2_log_update_head(sdp);
                }
                if (flags & (GFS2_LOG_HEAD_FLUSH_SHUTDOWN |
                             GFS2_LOG_HEAD_FLUSH_FREEZE))
@@ -1156,7 +1160,7 @@ static void gfs2_log_shutdown(struct gfs2_sbd *sdp)
        gfs2_assert_warn(sdp, sdp->sd_log_head == sdp->sd_log_tail);
        gfs2_assert_warn(sdp, list_empty(&sdp->sd_ail2_list));
 
-       sdp->sd_log_head = sdp->sd_log_flush_head;
+       gfs2_log_update_head(sdp);
        sdp->sd_log_tail = sdp->sd_log_head;
 }
 

diff --git a/fs/gfs2/log.h b/fs/gfs2/log.h
index cbc097c..b36a353 100644 (file)
--- a/fs/gfs2/log.h
+++ b/fs/gfs2/log.h
@@ -43,7 +43,9 @@ static inline void gfs2_log_pointers_init(struct gfs2_sbd *sdp,
        if (++value == sdp->sd_jdesc->jd_blocks) {
                value = 0;
        }
-       sdp->sd_log_head = sdp->sd_log_tail = value;
+       sdp->sd_log_tail = value;
+       sdp->sd_log_flush_tail = value;
+       sdp->sd_log_head = value;
 }
 
 static inline void gfs2_ordered_add_inode(struct gfs2_inode *ip)