[PATCH] JFFS2: Dynamically choose inocache hash size

[Daniel Drake]

When JFFS2 is used for large volumes, the mount times are quite long.
Increasing the hash size provides a significant speed boost on the OLPC
XO-1 laptop.

Add logic that dynamically selects a hash size based on the size of
the medium. A 64mb medium will result in a hash size of 128, and a 512mb
medium will result in a hash size of 1024.

Signed-off-by: Daniel Drake <dsd at laptop.org>
---
 fs/jffs2/build.c       |    2 +-
 fs/jffs2/fs.c          |   22 +++++++++++++++++++++-
 fs/jffs2/jffs2_fs_sb.h |    1 +
 fs/jffs2/nodelist.c    |    8 ++++----
 fs/jffs2/nodelist.h    |    3 ++-
 5 files changed, 29 insertions(+), 7 deletions(-)

Yesterday I wrote saying this patch didn't work. It's actually working fine.
The problem was that I was comparing linus tree to linux-next (with this
patch applied), and linux-next introduced a bug:
http://www.spinics.net/lists/linux-fsdevel/msg37534.html
This seems to be already fixed in more recent linux-next as well.

diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
index a906f53..85c6be2 100644
--- a/fs/jffs2/build.c
+++ b/fs/jffs2/build.c
@@ -23,7 +23,7 @@ static void jffs2_build_remove_unlinked_inode(struct jffs2_sb_info *,
 static inline struct jffs2_inode_cache *
 first_inode_chain(int *i, struct jffs2_sb_info *c)
 {
-	for (; *i < INOCACHE_HASHSIZE; (*i)++) {
+	for (; *i < c->inocache_hashsize; (*i)++) {
 		if (c->inocache_list[*i])
 			return c->inocache_list[*i];
 	}
diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
index 6b2964a..2701b37 100644
--- a/fs/jffs2/fs.c
+++ b/fs/jffs2/fs.c
@@ -478,6 +478,25 @@ struct inode *jffs2_new_inode (struct inode *dir_i, int mode, struct jffs2_raw_i
 	return inode;
 }
 
+static int calculate_inocache_hashsize(uint32_t flash_size)
+{
+	/*
+	 * Pick a inocache hash size based on the size of the medium.
+	 * Count how many megabytes we're dealing with, apply a hashsize twice
+	 * that size, but rounding down to the usual big powers of 2. And keep
+	 * to sensible bounds.
+	 */
+
+	int size_mb = flash_size / 1024 / 1024;
+	int hashsize = (size_mb * 2) & ~0x3f;
+
+	if (hashsize < INOCACHE_HASHSIZE_MIN)
+		return INOCACHE_HASHSIZE_MIN;
+	if (hashsize > INOCACHE_HASHSIZE_MAX)
+		return INOCACHE_HASHSIZE_MAX;
+
+	return hashsize;
+}
 
 int jffs2_do_fill_super(struct super_block *sb, void *data, int silent)
 {
@@ -524,7 +543,8 @@ int jffs2_do_fill_super(struct super_block *sb, void *data, int silent)
 	if (ret)
 		return ret;
 
-	c->inocache_list = kcalloc(INOCACHE_HASHSIZE, sizeof(struct jffs2_inode_cache *), GFP_KERNEL);
+	c->inocache_hashsize = calculate_inocache_hashsize(c->flash_size);
+	c->inocache_list = kcalloc(c->inocache_hashsize, sizeof(struct jffs2_inode_cache *), GFP_KERNEL);
 	if (!c->inocache_list) {
 		ret = -ENOMEM;
 		goto out_wbuf;
diff --git a/fs/jffs2/jffs2_fs_sb.h b/fs/jffs2/jffs2_fs_sb.h
index 6784bc8..f864005 100644
--- a/fs/jffs2/jffs2_fs_sb.h
+++ b/fs/jffs2/jffs2_fs_sb.h
@@ -100,6 +100,7 @@ struct jffs2_sb_info {
 	wait_queue_head_t erase_wait;		/* For waiting for erases to complete */
 
 	wait_queue_head_t inocache_wq;
+	int inocache_hashsize;
 	struct jffs2_inode_cache **inocache_list;
 	spinlock_t inocache_lock;
 
diff --git a/fs/jffs2/nodelist.c b/fs/jffs2/nodelist.c
index af02bd1..5e03233 100644
--- a/fs/jffs2/nodelist.c
+++ b/fs/jffs2/nodelist.c
@@ -420,7 +420,7 @@ struct jffs2_inode_cache *jffs2_get_ino_cache(struct jffs2_sb_info *c, uint32_t
 {
 	struct jffs2_inode_cache *ret;
 
-	ret = c->inocache_list[ino % INOCACHE_HASHSIZE];
+	ret = c->inocache_list[ino % c->inocache_hashsize];
 	while (ret && ret->ino < ino) {
 		ret = ret->next;
 	}
@@ -441,7 +441,7 @@ void jffs2_add_ino_cache (struct jffs2_sb_info *c, struct jffs2_inode_cache *new
 
 	dbg_inocache("add %p (ino #%u)\n", new, new->ino);
 
-	prev = &c->inocache_list[new->ino % INOCACHE_HASHSIZE];
+	prev = &c->inocache_list[new->ino % c->inocache_hashsize];
 
 	while ((*prev) && (*prev)->ino < new->ino) {
 		prev = &(*prev)->next;
@@ -462,7 +462,7 @@ void jffs2_del_ino_cache(struct jffs2_sb_info *c, struct jffs2_inode_cache *old)
 	dbg_inocache("del %p (ino #%u)\n", old, old->ino);
 	spin_lock(&c->inocache_lock);
 
-	prev = &c->inocache_list[old->ino % INOCACHE_HASHSIZE];
+	prev = &c->inocache_list[old->ino % c->inocache_hashsize];
 
 	while ((*prev) && (*prev)->ino < old->ino) {
 		prev = &(*prev)->next;
@@ -487,7 +487,7 @@ void jffs2_free_ino_caches(struct jffs2_sb_info *c)
 	int i;
 	struct jffs2_inode_cache *this, *next;
 
-	for (i=0; i<INOCACHE_HASHSIZE; i++) {
+	for (i=0; i < c->inocache_hashsize; i++) {
 		this = c->inocache_list[i];
 		while (this) {
 			next = this->next;
diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
index 523a916..5a53d9b 100644
--- a/fs/jffs2/nodelist.h
+++ b/fs/jffs2/nodelist.h
@@ -199,7 +199,8 @@ struct jffs2_inode_cache {
 #define RAWNODE_CLASS_XATTR_DATUM	1
 #define RAWNODE_CLASS_XATTR_REF		2
 
-#define INOCACHE_HASHSIZE 128
+#define INOCACHE_HASHSIZE_MIN 128
+#define INOCACHE_HASHSIZE_MAX 1024
 
 #define write_ofs(c) ((c)->nextblock->offset + (c)->sector_size - (c)->nextblock->free_size)
 
-- 
1.7.2.3