GFS2: Kill two daemons with one patch

This patch removes the two daemons, gfs2_scand and gfs2_glockd
and replaces them with a shrinker which is called from the VM.

The net result is that GFS2 responds better when there is memory
pressure, since it shrinks the glock cache at the same rate
as the VFS shrinks the dcache and icache. There are no longer
any time based criteria for shrinking glocks, they are kept
until such time as the VM asks for more memory and then we
demote just as many glocks as required.

There are potential future changes to this code, including the
possibility of sorting the glocks which are to be written back
into inode number order, to get a better I/O ordering. It would
be very useful to have an elevator based workqueue implementation
for this, as that would automatically deal with the read I/O cases
at the same time.

This patch is my answer to Andrew Morton's remark, made during
the initial review of GFS2, asking why GFS2 needs so many kernel
threads, the answer being that it doesn't :-) This patch is a
net loss of about 200 lines of code.

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

1 files changed, 19 insertions, 13 deletions

diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 8ebff8ebae20..8522d3aa64fc 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -201,19 +201,12 @@ static void inode_go_inval(struct gfs2_glock *gl, int flags)
  * Returns: 1 if it's ok
  */
 
-static int inode_go_demote_ok(struct gfs2_glock *gl)
+static int inode_go_demote_ok(const struct gfs2_glock *gl)
 {
         struct gfs2_sbd *sdp = gl->gl_sbd;
-        int demote = 0;
-
-        if (!gl->gl_object && !gl->gl_aspace->i_mapping->nrpages)
-                demote = 1;
-        else if (!sdp->sd_args.ar_localcaching &&
-                 time_after_eq(jiffies, gl->gl_stamp +
-                               gfs2_tune_get(sdp, gt_demote_secs) * HZ))
-                demote = 1;
-
-        return demote;
+        if (sdp->sd_jindex == gl->gl_object || sdp->sd_rindex == gl->gl_object)
+                return 0;
+        return 1;
 }
 
 /**
@@ -284,7 +277,7 @@ static int inode_go_dump(struct seq_file *seq, const struct gfs2_glock *gl)
  * Returns: 1 if it's ok
  */
 
-static int rgrp_go_demote_ok(struct gfs2_glock *gl)
+static int rgrp_go_demote_ok(const struct gfs2_glock *gl)
 {
         return !gl->gl_aspace->i_mapping->nrpages;
 }
@@ -386,13 +379,25 @@ static int trans_go_xmote_bh(struct gfs2_glock *gl, struct gfs2_holder *gh)
 }
 
 /**
+ * trans_go_demote_ok
+ * @gl: the glock
+ *
+ * Always returns 0
+ */
+
+static int trans_go_demote_ok(const struct gfs2_glock *gl)
+{
+        return 0;
+}
+
+/**
  * quota_go_demote_ok - Check to see if it's ok to unlock a quota glock
  * @gl: the glock
  *
  * Returns: 1 if it's ok
  */
 
-static int quota_go_demote_ok(struct gfs2_glock *gl)
+static int quota_go_demote_ok(const struct gfs2_glock *gl)
 {
         return !atomic_read(&gl->gl_lvb_count);
 }
@@ -426,6 +431,7 @@ const struct gfs2_glock_operations gfs2_rgrp_glops = {
 const struct gfs2_glock_operations gfs2_trans_glops = {
         .go_xmote_th = trans_go_sync,
         .go_xmote_bh = trans_go_xmote_bh,
+        .go_demote_ok = trans_go_demote_ok,
         .go_type = LM_TYPE_NONDISK,
 };