fs: split __shrink_dcache_sb

Currently __shrink_dcache_sb has an extremly awkward calling convention
because it tries to please very different callers.  Split out the
main loop into a shrink_dentry_list helper, which gets called directly
from shrink_dcache_sb for the cases where all dentries need to be pruned,
or from __shrink_dcache_sb for pruning only a certain number of dentries.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 67 insertions, 60 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 1a976d4efbe1..e987ad576a39 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -459,66 +459,20 @@ static void prune_one_dentry(struct dentry * dentry)
         }
 }
 
-/*
- * Shrink the dentry LRU on a given superblock.
- * @sb   : superblock to shrink dentry LRU.
- * @count: If count is NULL, we prune all dentries on superblock.
- * @flags: If flags is non-zero, we need to do special processing based on
- * which flags are set. This means we don't need to maintain multiple
- * similar copies of this loop.
- */
-static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags)
+static void shrink_dentry_list(struct list_head *list)
 {
-        LIST_HEAD(referenced);
-        LIST_HEAD(tmp);
         struct dentry *dentry;
-        int cnt = 0;
 
-        BUG_ON(!sb);
-        BUG_ON((flags & DCACHE_REFERENCED) && count == NULL);
-        spin_lock(&dcache_lock);
-        if (count != NULL)
-                /* called from prune_dcache() and shrink_dcache_parent() */
-                cnt = *count;
-restart:
-        if (count == NULL)
-                list_splice_init(&sb->s_dentry_lru, &tmp);
-        else {
-                while (!list_empty(&sb->s_dentry_lru)) {
-                        dentry = list_entry(sb->s_dentry_lru.prev,
-                                        struct dentry, d_lru);
-                        BUG_ON(dentry->d_sb != sb);
-
-                        spin_lock(&dentry->d_lock);
-                        /*
-                         * If we are honouring the DCACHE_REFERENCED flag and
-                         * the dentry has this flag set, don't free it. Clear
-                         * the flag and put it back on the LRU.
-                         */
-                        if ((flags & DCACHE_REFERENCED)
-                                && (dentry->d_flags & DCACHE_REFERENCED)) {
-                                dentry->d_flags &= ~DCACHE_REFERENCED;
-                                list_move(&dentry->d_lru, &referenced);
-                                spin_unlock(&dentry->d_lock);
-                        } else {
-                                list_move_tail(&dentry->d_lru, &tmp);
-                                spin_unlock(&dentry->d_lock);
-                                cnt--;
-                                if (!cnt)
-                                        break;
-                        }
-                        cond_resched_lock(&dcache_lock);
-                }
-        }
-        while (!list_empty(&tmp)) {
-                dentry = list_entry(tmp.prev, struct dentry, d_lru);
+        while (!list_empty(list)) {
+                dentry = list_entry(list->prev, struct dentry, d_lru);
                 dentry_lru_del_init(dentry);
-                spin_lock(&dentry->d_lock);
+
                 /*
                  * We found an inuse dentry which was not removed from
                  * the LRU because of laziness during lookup.  Do not free
                  * it - just keep it off the LRU list.
                  */
+                spin_lock(&dentry->d_lock);
                 if (atomic_read(&dentry->d_count)) {
                         spin_unlock(&dentry->d_lock);
                         continue;
@@ -527,13 +481,60 @@ restart:
                 /* dentry->d_lock was dropped in prune_one_dentry() */
                 cond_resched_lock(&dcache_lock);
         }
-        if (count == NULL && !list_empty(&sb->s_dentry_lru))
-                goto restart;
-        if (count != NULL)
-                *count = cnt;
+}
+
+/**
+ * __shrink_dcache_sb - shrink the dentry LRU on a given superblock
+ * @sb:         superblock to shrink dentry LRU.
+ * @count:      number of entries to prune
+ * @flags:      flags to control the dentry processing
+ *
+ * If flags contains DCACHE_REFERENCED reference dentries will not be pruned.
+ */
+static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags)
+{
+        /* called from prune_dcache() and shrink_dcache_parent() */
+        struct dentry *dentry;
+        LIST_HEAD(referenced);
+        LIST_HEAD(tmp);
+        int cnt = *count;
+
+        spin_lock(&dcache_lock);
+        while (!list_empty(&sb->s_dentry_lru)) {
+                dentry = list_entry(sb->s_dentry_lru.prev,
+                                struct dentry, d_lru);
+                BUG_ON(dentry->d_sb != sb);
+
+                /*
+                 * If we are honouring the DCACHE_REFERENCED flag and the
+                 * dentry has this flag set, don't free it.  Clear the flag
+                 * and put it back on the LRU.
+                 */
+                if (flags & DCACHE_REFERENCED) {
+                        spin_lock(&dentry->d_lock);
+                        if (dentry->d_flags & DCACHE_REFERENCED) {
+                                dentry->d_flags &= ~DCACHE_REFERENCED;
+                                list_move(&dentry->d_lru, &referenced);
+                                spin_unlock(&dentry->d_lock);
+                                cond_resched_lock(&dcache_lock);
+                                continue;
+                        }
+                        spin_unlock(&dentry->d_lock);
+                }
+
+                list_move_tail(&dentry->d_lru, &tmp);
+                if (!--cnt)
+                        break;
+                cond_resched_lock(&dcache_lock);
+        }
+
+        *count = cnt;
+        shrink_dentry_list(&tmp);
+
         if (!list_empty(&referenced))
                 list_splice(&referenced, &sb->s_dentry_lru);
         spin_unlock(&dcache_lock);
+
 }
 
 /**
@@ -619,13 +620,19 @@ static void prune_dcache(int count)
  * shrink_dcache_sb - shrink dcache for a superblock
  * @sb: superblock
  *
- * Shrink the dcache for the specified super block. This
- * is used to free the dcache before unmounting a file
- * system
+ * Shrink the dcache for the specified super block. This is used to free
+ * the dcache before unmounting a file system.
  */
-void shrink_dcache_sb(struct super_block * sb)
+void shrink_dcache_sb(struct super_block *sb)
 {
-        __shrink_dcache_sb(sb, NULL, 0);
+        LIST_HEAD(tmp);
+
+        spin_lock(&dcache_lock);
+        while (!list_empty(&sb->s_dentry_lru)) {
+                list_splice_init(&sb->s_dentry_lru, &tmp);
+                shrink_dentry_list(&tmp);
+        }
+        spin_unlock(&dcache_lock);
 }
 EXPORT_SYMBOL(shrink_dcache_sb);