quota: Make quota stat accounting lockless.

Quota stats is mostly writable data structure. Let's alloc percpu
bucket for each value.

NOTE: dqstats_read() function is racy against dqstats_{inc,dec}
and may return inconsistent value. But this is ok since absolute
accuracy is not required.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 68 insertions, 34 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index ae766056350d..01347e81d0ca 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -82,7 +82,7 @@
 
 /*
  * There are three quota SMP locks. dq_list_lock protects all lists with quotas
- * and quota formats, dqstats structure containing statistics about the lists
+ * and quota formats.
  * dq_data_lock protects data from dq_dqb and also mem_dqinfo structures and
  * also guards consistency of dquot->dq_dqb with inode->i_blocks, i_bytes.
  * i_blocks and i_bytes updates itself are guarded by i_lock acquired directly
@@ -228,6 +228,10 @@ static struct hlist_head *dquot_hash;
 
 struct dqstats dqstats;
 EXPORT_SYMBOL(dqstats);
+#ifdef CONFIG_SMP
+struct dqstats *dqstats_pcpu;
+EXPORT_SYMBOL(dqstats_pcpu);
+#endif
 
 static qsize_t inode_get_rsv_space(struct inode *inode);
 static void __dquot_initialize(struct inode *inode, int type);
@@ -275,7 +279,7 @@ static struct dquot *find_dquot(unsigned int hashent, struct super_block *sb,
 static inline void put_dquot_last(struct dquot *dquot)
 {
         list_add_tail(&dquot->dq_free, &free_dquots);
-        dqstats.free_dquots++;
+        dqstats_inc(DQST_FREE_DQUOTS);
 }
 
 static inline void remove_free_dquot(struct dquot *dquot)
@@ -283,7 +287,7 @@ static inline void remove_free_dquot(struct dquot *dquot)
         if (list_empty(&dquot->dq_free))
                 return;
         list_del_init(&dquot->dq_free);
-        dqstats.free_dquots--;
+        dqstats_dec(DQST_FREE_DQUOTS);
 }
 
 static inline void put_inuse(struct dquot *dquot)
@@ -291,12 +295,12 @@ static inline void put_inuse(struct dquot *dquot)
         /* We add to the back of inuse list so we don't have to restart
          * when traversing this list and we block */
         list_add_tail(&dquot->dq_inuse, &inuse_list);
-        dqstats.allocated_dquots++;
+        dqstats_inc(DQST_ALLOC_DQUOTS);
 }
 
 static inline void remove_inuse(struct dquot *dquot)
 {
-        dqstats.allocated_dquots--;
+        dqstats_dec(DQST_ALLOC_DQUOTS);
         list_del(&dquot->dq_inuse);
 }
 /*
@@ -561,8 +565,8 @@ int dquot_scan_active(struct super_block *sb,
                         continue;
                 /* Now we have active dquot so we can just increase use count */
                 atomic_inc(&dquot->dq_count);
-                dqstats.lookups++;
                 spin_unlock(&dq_list_lock);
+                dqstats_inc(DQST_LOOKUPS);
                 dqput(old_dquot);
                 old_dquot = dquot;
                 ret = fn(dquot, priv);
@@ -607,8 +611,8 @@ int vfs_quota_sync(struct super_block *sb, int type, int wait)
                          * holding reference so we can safely just increase
                          * use count */
                         atomic_inc(&dquot->dq_count);
-                        dqstats.lookups++;
                         spin_unlock(&dq_list_lock);
+                        dqstats_inc(DQST_LOOKUPS);
                         sb->dq_op->write_dquot(dquot);
                         dqput(dquot);
                         spin_lock(&dq_list_lock);
@@ -620,9 +624,7 @@ int vfs_quota_sync(struct super_block *sb, int type, int wait)
                 if ((cnt == type || type == -1) && sb_has_quota_active(sb, cnt)
                     && info_dirty(&dqopt->info[cnt]))
                         sb->dq_op->write_info(sb, cnt);
-        spin_lock(&dq_list_lock);
-        dqstats.syncs++;
-        spin_unlock(&dq_list_lock);
+        dqstats_inc(DQST_SYNCS);
         mutex_unlock(&dqopt->dqonoff_mutex);
 
         if (!wait || (sb_dqopt(sb)->flags & DQUOT_QUOTA_SYS_FILE))
@@ -674,6 +676,22 @@ static void prune_dqcache(int count)
         }
 }
 
+static int dqstats_read(unsigned int type)
+{
+        int count = 0;
+#ifdef CONFIG_SMP
+        int cpu;
+        for_each_possible_cpu(cpu)
+                count += per_cpu_ptr(dqstats_pcpu, cpu)->stat[type];
+        /* Statistics reading is racy, but absolute accuracy isn't required */
+        if (count < 0)
+                count = 0;
+#else
+        count = dqstats.stat[type];
+#endif
+        return count;
+}
+
 /*
  * This is called from kswapd when we think we need some
  * more memory
@@ -686,7 +704,7 @@ static int shrink_dqcache_memory(int nr, gfp_t gfp_mask)
                 prune_dqcache(nr);
                 spin_unlock(&dq_list_lock);
         }
-        return (dqstats.free_dquots / 100) * sysctl_vfs_cache_pressure;
+        return (dqstats_read(DQST_FREE_DQUOTS)/100) * sysctl_vfs_cache_pressure;
 }
 
 static struct shrinker dqcache_shrinker = {
@@ -714,10 +732,7 @@ void dqput(struct dquot *dquot)
                 BUG();
         }
 #endif
-        
-        spin_lock(&dq_list_lock);
-        dqstats.drops++;
-        spin_unlock(&dq_list_lock);
+        dqstats_inc(DQST_DROPS);
 we_slept:
         spin_lock(&dq_list_lock);
         if (atomic_read(&dquot->dq_count) > 1) {
@@ -834,15 +849,15 @@ we_slept:
                 put_inuse(dquot);
                 /* hash it first so it can be found */
                 insert_dquot_hash(dquot);
-                dqstats.lookups++;
                 spin_unlock(&dq_list_lock);
+                dqstats_inc(DQST_LOOKUPS);
         } else {
                 if (!atomic_read(&dquot->dq_count))
                         remove_free_dquot(dquot);
                 atomic_inc(&dquot->dq_count);
-                dqstats.cache_hits++;
-                dqstats.lookups++;
                 spin_unlock(&dq_list_lock);
+                dqstats_inc(DQST_CACHE_HITS);
+                dqstats_inc(DQST_LOOKUPS);
         }
         /* Wait for dq_lock - after this we know that either dquot_release() is
          * already finished or it will be canceled due to dq_count > 1 test */
@@ -2476,62 +2491,74 @@ const struct quotactl_ops vfs_quotactl_ops = {
         .set_dqblk      = vfs_set_dqblk
 };
 
+
+static int do_proc_dqstats(struct ctl_table *table, int write,
+                     void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+#ifdef CONFIG_SMP
+        /* Update global table */
+        unsigned int type = (int *)table->data - dqstats.stat;
+        dqstats.stat[type] = dqstats_read(type);
+#endif
+        return proc_dointvec(table, write, buffer, lenp, ppos);
+}
+
 static ctl_table fs_dqstats_table[] = {
         {
                 .procname       = "lookups",
-                .data           = &dqstats.lookups,
+                .data           = &dqstats.stat[DQST_LOOKUPS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "drops",
-                .data           = &dqstats.drops,
+                .data           = &dqstats.stat[DQST_DROPS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "reads",
-                .data           = &dqstats.reads,
+                .data           = &dqstats.stat[DQST_READS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "writes",
-                .data           = &dqstats.writes,
+                .data           = &dqstats.stat[DQST_WRITES],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "cache_hits",
-                .data           = &dqstats.cache_hits,
+                .data           = &dqstats.stat[DQST_CACHE_HITS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "allocated_dquots",
-                .data           = &dqstats.allocated_dquots,
+                .data           = &dqstats.stat[DQST_ALLOC_DQUOTS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "free_dquots",
-                .data           = &dqstats.free_dquots,
+                .data           = &dqstats.stat[DQST_FREE_DQUOTS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
         {
                 .procname       = "syncs",
-                .data           = &dqstats.syncs,
+                .data           = &dqstats.stat[DQST_SYNCS],
                 .maxlen         = sizeof(int),
                 .mode           = 0444,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = do_proc_dqstats,
         },
 #ifdef CONFIG_PRINT_QUOTA_WARNING
         {
@@ -2583,6 +2610,13 @@ static int __init dquot_init(void)
         if (!dquot_hash)
                 panic("Cannot create dquot hash table");
 
+#ifdef CONFIG_SMP
+        dqstats_pcpu = alloc_percpu(struct dqstats);
+        if (!dqstats_pcpu)
+                panic("Cannot create dquot stats table");
+#endif
+        memset(&dqstats, 0, sizeof(struct dqstats));
+
         /* Find power-of-two hlist_heads which can fit into allocation */
         nr_hash = (1UL << order) * PAGE_SIZE / sizeof(struct hlist_head);
         dq_hash_bits = 0;