3 files changed, 52 insertions, 13 deletions

diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt
index 819caf8ca05f..58649bd4fcfc 100644
--- a/Documentation/sysctl/fs.txt
+++ b/Documentation/sysctl/fs.txt
@@ -56,26 +56,32 @@ of any kernel data structures.
 
 dentry-state:
 
-From linux/fs/dentry.c:
+From linux/include/linux/dcache.h:
 --------------------------------------------------------------
-struct {
+struct dentry_stat_t dentry_stat {
         int nr_dentry;
         int nr_unused;
         int age_limit;         /* age in seconds */
         int want_pages;        /* pages requested by system */
-        int dummy[2];
-} dentry_stat = {0, 0, 45, 0,};
--------------------------------------------------------------- 
-
-Dentries are dynamically allocated and deallocated, and
-nr_dentry seems to be 0 all the time. Hence it's safe to
-assume that only nr_unused, age_limit and want_pages are
-used. Nr_unused seems to be exactly what its name says.
+        int nr_negative;       /* # of unused negative dentries */
+        int dummy;             /* Reserved for future use */
+};
+--------------------------------------------------------------
+
+Dentries are dynamically allocated and deallocated.
+
+nr_dentry shows the total number of dentries allocated (active
++ unused). nr_unused shows the number of dentries that are not
+actively used, but are saved in the LRU list for future reuse.
+
 Age_limit is the age in seconds after which dcache entries
 can be reclaimed when memory is short and want_pages is
 nonzero when shrink_dcache_pages() has been called and the
 dcache isn't pruned yet.
 
+nr_negative shows the number of unused dentries that are also
+negative dentries which do not mapped to actual files.
+
 ==============================================================
 
 dquot-max & dquot-nr:
diff --git a/fs/dcache.c b/fs/dcache.c
index 44e5652b2664..aac41adf4743 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -119,6 +119,7 @@ struct dentry_stat_t dentry_stat = {
 
 static DEFINE_PER_CPU(long, nr_dentry);
 static DEFINE_PER_CPU(long, nr_dentry_unused);
+static DEFINE_PER_CPU(long, nr_dentry_negative);
 
 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
 
@@ -152,11 +153,22 @@ static long get_nr_dentry_unused(void)
         return sum < 0 ? 0 : sum;
 }
 
+static long get_nr_dentry_negative(void)
+{
+        int i;
+        long sum = 0;
+
+        for_each_possible_cpu(i)
+                sum += per_cpu(nr_dentry_negative, i);
+        return sum < 0 ? 0 : sum;
+}
+
 int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
                    size_t *lenp, loff_t *ppos)
 {
         dentry_stat.nr_dentry = get_nr_dentry();
         dentry_stat.nr_unused = get_nr_dentry_unused();
+        dentry_stat.nr_negative = get_nr_dentry_negative();
         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
 #endif
@@ -317,6 +329,8 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry)
         flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
         WRITE_ONCE(dentry->d_flags, flags);
         dentry->d_inode = NULL;
+        if (dentry->d_flags & DCACHE_LRU_LIST)
+                this_cpu_inc(nr_dentry_negative);
 }
 
 static void dentry_free(struct dentry *dentry)
@@ -371,6 +385,11 @@ static void dentry_unlink_inode(struct dentry * dentry)
  * The per-cpu "nr_dentry_unused" counters are updated with
  * the DCACHE_LRU_LIST bit.
  *
+ * The per-cpu "nr_dentry_negative" counters are only updated
+ * when deleted from or added to the per-superblock LRU list, not
+ * from/to the shrink list. That is to avoid an unneeded dec/inc
+ * pair when moving from LRU to shrink list in select_collect().
+ *
  * These helper functions make sure we always follow the
  * rules. d_lock must be held by the caller.
  */
@@ -380,6 +399,8 @@ static void d_lru_add(struct dentry *dentry)
         D_FLAG_VERIFY(dentry, 0);
         dentry->d_flags |= DCACHE_LRU_LIST;
         this_cpu_inc(nr_dentry_unused);
+        if (d_is_negative(dentry))
+                this_cpu_inc(nr_dentry_negative);
         WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
 }
 
@@ -388,6 +409,8 @@ static void d_lru_del(struct dentry *dentry)
         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
         dentry->d_flags &= ~DCACHE_LRU_LIST;
         this_cpu_dec(nr_dentry_unused);
+        if (d_is_negative(dentry))
+                this_cpu_dec(nr_dentry_negative);
         WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
 }
 
@@ -418,6 +441,8 @@ static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
         dentry->d_flags &= ~DCACHE_LRU_LIST;
         this_cpu_dec(nr_dentry_unused);
+        if (d_is_negative(dentry))
+                this_cpu_dec(nr_dentry_negative);
         list_lru_isolate(lru, &dentry->d_lru);
 }
 
@@ -426,6 +451,8 @@ static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
 {
         D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
         dentry->d_flags |= DCACHE_SHRINK_LIST;
+        if (d_is_negative(dentry))
+                this_cpu_dec(nr_dentry_negative);
         list_lru_isolate_move(lru, &dentry->d_lru, list);
 }
 
@@ -1816,6 +1843,11 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
         WARN_ON(d_in_lookup(dentry));
 
         spin_lock(&dentry->d_lock);
+        /*
+         * Decrement negative dentry count if it was in the LRU list.
+         */
+        if (dentry->d_flags & DCACHE_LRU_LIST)
+                this_cpu_dec(nr_dentry_negative);
         hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
         raw_write_seqcount_begin(&dentry->d_seq);
         __d_set_inode_and_type(dentry, inode, add_flags);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index ef4b70f64f33..60996e64c579 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -62,9 +62,10 @@ extern const struct qstr slash_name;
 struct dentry_stat_t {
         long nr_dentry;
         long nr_unused;
-        long age_limit;          /* age in seconds */
-        long want_pages;         /* pages requested by system */
-        long dummy[2];
+        long age_limit;         /* age in seconds */
+        long want_pages;        /* pages requested by system */
+        long nr_negative;       /* # of unused negative dentries */
+        long dummy;             /* Reserved for future use */
 };
 extern struct dentry_stat_t dentry_stat;