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Date:	Thu,  6 Jan 2011 21:36:03 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH -v2] ext4: Dynamically allocate the jbd2_inode in ext4_inode_info as necessary

Replace the jbd2_inode structure (which is 48 bytes) with a pointer
and only allocate the jbd2_inode when it is needed --- that is, when
the file system has a journal present and the inode has been opened
for writing.  This allows us to further slim down the ext4_inode_info
structure.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---

I looked into release the jinode structure in ext4_release_file(), but
that doesn't work because we need to wait until the delayed allocation
is completed.  At some point I'll look into adding something that checks
to see if we have finished doing the background writeout, but I'm going
to save that for another patch.

 fs/ext4/ext4.h       |    2 +-
 fs/ext4/ext4_jbd2.h  |    2 +-
 fs/ext4/file.c       |   22 ++++++++++++++++++++++
 fs/ext4/inode.c      |   17 ++++++++++++-----
 fs/ext4/super.c      |   16 +++++++---------
 fs/jbd2/journal.c    |   20 +++++++++++++-------
 include/linux/jbd2.h |   20 ++++++++++++++++++--
 7 files changed, 74 insertions(+), 25 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 2569c23..2d20424 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -811,7 +811,7 @@ struct ext4_inode_info {
 	 */
 	struct rw_semaphore i_data_sem;
 	struct inode vfs_inode;
-	struct jbd2_inode jinode;
+	struct jbd2_inode *jinode;
 
 	struct ext4_ext_cache i_cached_extent;
 	/*
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index b0bd792..d8b992e 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -253,7 +253,7 @@ static inline int ext4_journal_force_commit(journal_t *journal)
 static inline int ext4_jbd2_file_inode(handle_t *handle, struct inode *inode)
 {
 	if (ext4_handle_valid(handle))
-		return jbd2_journal_file_inode(handle, &EXT4_I(inode)->jinode);
+		return jbd2_journal_file_inode(handle, EXT4_I(inode)->jinode);
 	return 0;
 }
 
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 5a5c55d..b1b4884 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -104,6 +104,7 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 {
 	struct super_block *sb = inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct ext4_inode_info *ei = EXT4_I(inode);
 	struct vfsmount *mnt = filp->f_path.mnt;
 	struct path path;
 	char buf[64], *cp;
@@ -127,6 +128,27 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 			ext4_mark_super_dirty(sb);
 		}
 	}
+	/*
+	 * Set up the jbd2_inode if we are opening the inode for
+	 * writing and the journal is present
+	 */
+	if (sbi->s_journal && !ei->jinode && (filp->f_mode & FMODE_WRITE)) {
+		struct jbd2_inode *jinode = jbd2_alloc_inode(GFP_KERNEL);
+
+		spin_lock(&inode->i_lock);
+		if (!ei->jinode) {
+			if (!jinode) {
+				spin_unlock(&inode->i_lock);
+				return -ENOMEM;
+			}
+			ei->jinode = jinode;
+			jbd2_journal_init_jbd_inode(ei->jinode, inode);
+			jinode = NULL;
+		}
+		if (unlikely(jinode != NULL))
+			jbd2_free_inode(jinode);
+		spin_unlock(&inode->i_lock);
+	}
 	return dquot_file_open(inode, filp);
 }
 
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d34ddc6..fb5fe73 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -55,10 +55,17 @@ static inline int ext4_begin_ordered_truncate(struct inode *inode,
 					      loff_t new_size)
 {
 	trace_ext4_begin_ordered_truncate(inode, new_size);
-	return jbd2_journal_begin_ordered_truncate(
-					EXT4_SB(inode->i_sb)->s_journal,
-					&EXT4_I(inode)->jinode,
-					new_size);
+	/*
+	 * If jinode is zero, then we never opened the file for
+	 * writing, so there's no need to call
+	 * jbd2_journal_begin_ordered_truncate() since there's no
+	 * outstanding writes we need to flush.
+	 */
+	if (!EXT4_I(inode)->jinode)
+		return 0;
+	return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
+						   EXT4_I(inode)->jinode,
+						   new_size);
 }
 
 static void ext4_invalidatepage(struct page *page, unsigned long offset);
@@ -4054,7 +4061,7 @@ int ext4_block_truncate_page(handle_t *handle,
 	if (ext4_should_journal_data(inode)) {
 		err = ext4_handle_dirty_metadata(handle, inode, bh);
 	} else {
-		if (ext4_should_order_data(inode))
+		if (ext4_should_order_data(inode) && EXT4_I(inode)->jinode)
 			err = ext4_jbd2_file_inode(handle, inode);
 		mark_buffer_dirty(bh);
 	}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f5960d6..1cd4326 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -818,12 +818,6 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
 	memset(&ei->i_cached_extent, 0, sizeof(struct ext4_ext_cache));
 	INIT_LIST_HEAD(&ei->i_prealloc_list);
 	spin_lock_init(&ei->i_prealloc_lock);
-	/*
-	 * Note:  We can be called before EXT4_SB(sb)->s_journal is set,
-	 * therefore it can be null here.  Don't check it, just initialize
-	 * jinode.
-	 */
-	jbd2_journal_init_jbd_inode(&ei->jinode, &ei->vfs_inode);
 	ei->i_reserved_data_blocks = 0;
 	ei->i_reserved_meta_blocks = 0;
 	ei->i_allocated_meta_blocks = 0;
@@ -832,6 +826,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
 #ifdef CONFIG_QUOTA
 	ei->i_reserved_quota = 0;
 #endif
+	ei->jinode = NULL;
 	INIT_LIST_HEAD(&ei->i_completed_io_list);
 	spin_lock_init(&ei->i_completed_io_lock);
 	ei->cur_aio_dio = NULL;
@@ -900,9 +895,12 @@ void ext4_clear_inode(struct inode *inode)
 	end_writeback(inode);
 	dquot_drop(inode);
 	ext4_discard_preallocations(inode);
-	if (EXT4_JOURNAL(inode))
-		jbd2_journal_release_jbd_inode(EXT4_SB(inode->i_sb)->s_journal,
-				       &EXT4_I(inode)->jinode);
+	if (EXT4_I(inode)->jinode) {
+		jbd2_journal_release_jbd_inode(EXT4_JOURNAL(inode),
+					       EXT4_I(inode)->jinode);
+		jbd2_free_inode(EXT4_I(inode)->jinode);
+		EXT4_I(inode)->jinode = NULL;
+	}
 }
 
 static inline void ext4_show_quota_options(struct seq_file *seq,
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2447bd8..9e46869 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -94,6 +94,7 @@ EXPORT_SYMBOL(jbd2_journal_file_inode);
 EXPORT_SYMBOL(jbd2_journal_init_jbd_inode);
 EXPORT_SYMBOL(jbd2_journal_release_jbd_inode);
 EXPORT_SYMBOL(jbd2_journal_begin_ordered_truncate);
+EXPORT_SYMBOL(jbd2_inode_cache);
 
 static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
 static void __journal_abort_soft (journal_t *journal, int errno);
@@ -2286,17 +2287,19 @@ static void __exit jbd2_remove_jbd_stats_proc_entry(void)
 
 #endif
 
-struct kmem_cache *jbd2_handle_cache;
+struct kmem_cache *jbd2_handle_cache, *jbd2_inode_cache;
 
 static int __init journal_init_handle_cache(void)
 {
-	jbd2_handle_cache = kmem_cache_create("jbd2_journal_handle",
-				sizeof(handle_t),
-				0,		/* offset */
-				SLAB_TEMPORARY,	/* flags */
-				NULL);		/* ctor */
+	jbd2_handle_cache = KMEM_CACHE(jbd2_journal_handle, SLAB_TEMPORARY);
 	if (jbd2_handle_cache == NULL) {
-		printk(KERN_EMERG "JBD: failed to create handle cache\n");
+		printk(KERN_EMERG "JBD2: failed to create handle cache\n");
+		return -ENOMEM;
+	}
+	jbd2_inode_cache = KMEM_CACHE(jbd2_inode, 0);
+	if (jbd2_inode_cache == NULL) {
+		printk(KERN_EMERG "JBD2: failed to create inode cache\n");
+		kmem_cache_destroy(jbd2_handle_cache);
 		return -ENOMEM;
 	}
 	return 0;
@@ -2306,6 +2309,9 @@ static void jbd2_journal_destroy_handle_cache(void)
 {
 	if (jbd2_handle_cache)
 		kmem_cache_destroy(jbd2_handle_cache);
+	if (jbd2_inode_cache)
+		kmem_cache_destroy(jbd2_inode_cache);
+
 }
 
 /*
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 2ae86aa..27e79c2 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -94,7 +94,7 @@ extern void jbd2_free(void *ptr, size_t size);
  *
  * This is an opaque datatype.
  **/
-typedef struct handle_s		handle_t;	/* Atomic operation type */
+typedef struct jbd2_journal_handle handle_t;	/* Atomic operation type */
 
 
 /**
@@ -416,7 +416,7 @@ struct jbd2_revoke_table_s;
  * in so it can be fixed later.
  */
 
-struct handle_s
+struct jbd2_journal_handle
 {
 	/* Which compound transaction is this update a part of? */
 	transaction_t		*h_transaction;
@@ -1158,6 +1158,22 @@ static inline void jbd2_free_handle(handle_t *handle)
 	kmem_cache_free(jbd2_handle_cache, handle);
 }
 
+/*
+ * jbd2_inode management (optional, for those file systems that want to use
+ * dynamically allocated jbd2_inode structures)
+ */
+extern struct kmem_cache *jbd2_inode_cache;
+
+static inline struct jbd2_inode *jbd2_alloc_inode(gfp_t gfp_flags)
+{
+	return kmem_cache_alloc(jbd2_inode_cache, gfp_flags);
+}
+
+static inline void jbd2_free_inode(struct jbd2_inode *jinode)
+{
+	kmem_cache_free(jbd2_inode_cache, jinode);
+}
+
 /* Primary revoke support */
 #define JOURNAL_REVOKE_DEFAULT_HASH 256
 extern int	   jbd2_journal_init_revoke(journal_t *, int);
-- 
1.7.3.1

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