gfs2: Per-revoke accounting in transactions

In the log, revokes are stored as a revoke descriptor (struct
gfs2_log_descriptor), followed by zero or more additional revoke blocks
(struct gfs2_meta_header).  On filesystems with a blocksize of 4k, the
revoke descriptor contains up to 503 revokes, and the metadata blocks
contain up to 509 revokes each.  We've so far been reserving space for
revokes in transactions in block granularity, so a lot more space than
necessary was being allocated and then released again.

This patch switches to assigning revokes to transactions individually
instead.  Initially, space for the revoke descriptor is reserved and
handed out to transactions.  When more revokes than that are reserved,
additional revoke blocks are added.  When the log is flushed, the space
for the additional revoke blocks is released, but we keep the space for
the revoke descriptor block allocated.

Transactions may still reserve more revokes than they will actually need
in the end, but now we won't overshoot the target as much, and by only
returning the space for excess revokes at log flush time, we further
reduce the amount of contention between processes.

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

1 files changed, 2 insertions, 6 deletions

diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index a067924341e3..8e32d569c8bf 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -136,19 +136,15 @@ void gfs2_ail_flush(struct gfs2_glock *gl, bool fsync)
 {
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
 	unsigned int revokes = atomic_read(&gl->gl_ail_count);
-	unsigned int max_revokes = (sdp->sd_sb.sb_bsize - sizeof(struct gfs2_log_descriptor)) / sizeof(u64);
 	int ret;
 
 	if (!revokes)
 		return;
 
-	while (revokes > max_revokes)
-		max_revokes += (sdp->sd_sb.sb_bsize - sizeof(struct gfs2_meta_header)) / sizeof(u64);
-
-	ret = gfs2_trans_begin(sdp, 0, max_revokes);
+	ret = gfs2_trans_begin(sdp, 0, revokes);
 	if (ret)
 		return;
-	__gfs2_ail_flush(gl, fsync, max_revokes);
+	__gfs2_ail_flush(gl, fsync, revokes);
 	gfs2_trans_end(sdp);
 	gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
 		       GFS2_LFC_AIL_FLUSH);