[GFS2] Rewrite of examine_bucket()

The existing implementation of this function in glock.c was not
very efficient as it relied upon keeping a cursor element upon the
hash chain in question and moving it along. This new version improves
upon this by using the current element as a cursor. This is possible
since we only look at the "next" element in the list after we've
taken the read_lock() subsequent to calling the examiner function.
Obviously we have to eventually drop the ref count that we are then
left with and we cannot do that while holding the read_lock, so we
do that next time we drop the lock. That means either just before
we examine another glock, or when the loop has terminated.

The new implementation has several advantages: it uses only a
read_lock() rather than a write_lock(), so it can run simnultaneously
with other code, it doesn't need a "plug" element, so that it removes
a test not only from this list iterator, but from all the other glock
list iterators too. So it makes things faster and smaller.

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

1 files changed, 31 insertions, 64 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index b348053c4363..b5effb9e4a38 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -18,6 +18,7 @@
 #include <linux/kref.h>
 #include <linux/kallsyms.h>
 #include <linux/gfs2_ondisk.h>
+#include <linux/list.h>
 #include <asm/uaccess.h>
 
 #include "gfs2.h"
@@ -33,12 +34,6 @@
 #include "super.h"
 #include "util.h"
 
-/*  Must be kept in sync with the beginning of struct gfs2_glock  */
-struct glock_plug {
-        struct list_head gl_list;
-        unsigned long gl_flags;
-};
-
 struct greedy {
         struct gfs2_holder gr_gh;
         struct work_struct gr_work;
@@ -52,6 +47,7 @@ typedef void (*glock_examiner) (struct gfs2_glock * gl);
 
 static int gfs2_dump_lockstate(struct gfs2_sbd *sdp);
 static int dump_glock(struct gfs2_glock *gl);
+static int dump_inode(struct gfs2_inode *ip);
 
 #define GFS2_GL_HASH_SHIFT      13
 #define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
@@ -214,7 +210,7 @@ int gfs2_glock_put(struct gfs2_glock *gl)
 
         write_lock(gl_lock_addr(gl->gl_hash));
         if (kref_put(&gl->gl_ref, kill_glock)) {
-                list_del_init(&gl_hash_table[gl->gl_hash].hb_list);
+                list_del_init(&gl->gl_list);
                 write_unlock(gl_lock_addr(gl->gl_hash));
                 BUG_ON(spin_is_locked(&gl->gl_spin));
                 glock_free(gl);
@@ -265,8 +261,6 @@ static struct gfs2_glock *search_bucket(unsigned int hash,
         struct gfs2_glock *gl;
 
         list_for_each_entry(gl, &gl_hash_table[hash].hb_list, gl_list) {
-                if (test_bit(GLF_PLUG, &gl->gl_flags))
-                        continue;
                 if (!lm_name_equal(&gl->gl_name, name))
                         continue;
                 if (gl->gl_sbd != sdp)
@@ -1899,51 +1893,33 @@ void gfs2_reclaim_glock(struct gfs2_sbd *sdp)
 static int examine_bucket(glock_examiner examiner, struct gfs2_sbd *sdp,
                           unsigned int hash)
 {
-        struct glock_plug plug;
-        struct list_head *tmp;
-        struct gfs2_glock *gl;
-        int entries;
-
-        /* Add "plug" to end of bucket list, work back up list from there */
-        memset(&plug.gl_flags, 0, sizeof(unsigned long));
-        set_bit(GLF_PLUG, &plug.gl_flags);
-
-        write_lock(gl_lock_addr(hash));
-        list_add(&plug.gl_list, &gl_hash_table[hash].hb_list);
-        write_unlock(gl_lock_addr(hash));
-
-        for (;;) {
-                write_lock(gl_lock_addr(hash));
-
-                for (;;) {
-                        tmp = plug.gl_list.next;
+        struct gfs2_glock *gl, *prev = NULL;
+        int has_entries = 0;
+        struct list_head *head = &gl_hash_table[hash].hb_list;
 
-                        if (tmp == &gl_hash_table[hash].hb_list) {
-                                list_del(&plug.gl_list);
-                                entries = !list_empty(&gl_hash_table[hash].hb_list);
-                                write_unlock(gl_lock_addr(hash));
-                                return entries;
-                        }
-                        gl = list_entry(tmp, struct gfs2_glock, gl_list);
-
-                        /* Move plug up list */
-                        list_move(&plug.gl_list, &gl->gl_list);
-
-                        if (test_bit(GLF_PLUG, &gl->gl_flags))
-                                continue;
-                        if (gl->gl_sbd != sdp)
-                                continue;
-
-                        /* examiner() must glock_put() */
+        read_lock(gl_lock_addr(hash));
+        /* Can't use list_for_each_entry - don't want prefetch here */
+        if (list_empty(head))
+                goto out;
+        has_entries = 1;
+        gl = list_entry(head->next, struct gfs2_glock, gl_list);
+        while(&gl->gl_list != head) {
+                if (gl->gl_sbd == sdp) {
                         gfs2_glock_hold(gl);
-
-                        break;
+                        read_unlock(gl_lock_addr(hash));
+                        if (prev)
+                                gfs2_glock_put(prev);
+                        prev = gl;
+                        examiner(gl);
+                        read_lock(gl_lock_addr(hash));
                 }
-
-                write_unlock(gl_lock_addr(hash));
-
-                examiner(gl);
+                gl = list_entry(gl->gl_list.next, struct gfs2_glock, gl_list);
         }
+out:
+        read_unlock(gl_lock_addr(hash));
+        if (prev)
+                gfs2_glock_put(prev);
+        return has_entries;
 }
 
 /**
@@ -1955,23 +1931,19 @@ static int examine_bucket(glock_examiner examiner, struct gfs2_sbd *sdp,
 static void scan_glock(struct gfs2_glock *gl)
 {
         if (gl->gl_ops == &gfs2_inode_glops)
-                goto out;
+                return;
 
         if (gfs2_glmutex_trylock(gl)) {
                 if (queue_empty(gl, &gl->gl_holders) &&
-                    gl->gl_state != LM_ST_UNLOCKED &&
-                    demote_ok(gl))
+                    gl->gl_state != LM_ST_UNLOCKED && demote_ok(gl))
                         goto out_schedule;
                 gfs2_glmutex_unlock(gl);
         }
-out:
-        gfs2_glock_put(gl);
         return;
 
 out_schedule:
         gfs2_glmutex_unlock(gl);
         gfs2_glock_schedule_for_reclaim(gl);
-        gfs2_glock_put(gl);
 }
 
 /**
@@ -2014,11 +1986,8 @@ static void clear_glock(struct gfs2_glock *gl)
                 if (queue_empty(gl, &gl->gl_holders) &&
                     gl->gl_state != LM_ST_UNLOCKED)
                         handle_callback(gl, LM_ST_UNLOCKED);
-
                 gfs2_glmutex_unlock(gl);
         }
-
-        gfs2_glock_put(gl);
 }
 
 /**
@@ -2040,10 +2009,10 @@ void gfs2_gl_hash_clear(struct gfs2_sbd *sdp, int wait)
 
         for (;;) {
                 cont = 0;
-
-                for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
-                        if (examine_bucket(clear_glock, sdp, x))
+                for (x = 0; x < GFS2_GL_HASH_SIZE; x++) {
+                        if (examine_bucket(clear_glock, sdp, x)) 
                                 cont = 1;
+                }
 
                 if (!wait || !cont)
                         break;
@@ -2234,8 +2203,6 @@ static int gfs2_dump_lockstate(struct gfs2_sbd *sdp)
                 read_lock(gl_lock_addr(x));
 
                 list_for_each_entry(gl, &gl_hash_table[x].hb_list, gl_list) {
-                        if (test_bit(GLF_PLUG, &gl->gl_flags))
-                                continue;
                         if (gl->gl_sbd != sdp)
                                 continue;