From fa0d7e3de6d6fc5004ad9dea0dd6b286af8f03e9 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:49 +1100 Subject: fs: icache RCU free inodes RCU free the struct inode. This will allow: - Subsequent store-free path walking patch. The inode must be consulted for permissions when walking, so an RCU inode reference is a must. - sb_inode_list_lock to be moved inside i_lock because sb list walkers who want to take i_lock no longer need to take sb_inode_list_lock to walk the list in the first place. This will simplify and optimize locking. - Could remove some nested trylock loops in dcache code - Could potentially simplify things a bit in VM land. Do not need to take the page lock to follow page->mapping. The downsides of this is the performance cost of using RCU. In a simple creat/unlink microbenchmark, performance drops by about 10% due to inability to reuse cache-hot slab objects. As iterations increase and RCU freeing starts kicking over, this increases to about 20%. In cases where inode lifetimes are longer (ie. many inodes may be allocated during the average life span of a single inode), a lot of this cache reuse is not applicable, so the regression caused by this patch is smaller. The cache-hot regression could largely be avoided by using SLAB_DESTROY_BY_RCU, however this adds some complexity to list walking and store-free path walking, so I prefer to implement this at a later date, if it is shown to be a win in real situations. I haven't found a regression in any non-micro benchmark so I doubt it will be a problem. Signed-off-by: Nick Piggin --- fs/fat/inode.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'fs/fat/inode.c') diff --git a/fs/fat/inode.c b/fs/fat/inode.c index ad6998a92c30..8cccfebee180 100644 --- a/fs/fat/inode.c +++ b/fs/fat/inode.c @@ -514,11 +514,18 @@ static struct inode *fat_alloc_inode(struct super_block *sb) return &ei->vfs_inode; } -static void fat_destroy_inode(struct inode *inode) +static void fat_i_callback(struct rcu_head *head) { + struct inode *inode = container_of(head, struct inode, i_rcu); + INIT_LIST_HEAD(&inode->i_dentry); kmem_cache_free(fat_inode_cachep, MSDOS_I(inode)); } +static void fat_destroy_inode(struct inode *inode) +{ + call_rcu(&inode->i_rcu, fat_i_callback); +} + static void init_once(void *foo) { struct msdos_inode_info *ei = (struct msdos_inode_info *)foo; -- cgit v1.2.3 From fb045adb99d9b7c562dc7fef834857f78249daa1 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:55 +1100 Subject: fs: dcache reduce branches in lookup path Reduce some branches and memory accesses in dcache lookup by adding dentry flags to indicate common d_ops are set, rather than having to check them. This saves a pointer memory access (dentry->d_op) in common path lookup situations, and saves another pointer load and branch in cases where we have d_op but not the particular operation. Patched with: git grep -E '[.>]([[:space:]])*d_op([[:space:]])*=' | xargs sed -e 's/\([^\t ]*\)->d_op = \(.*\);/d_set_d_op(\1, \2);/' -e 's/\([^\t ]*\)\.d_op = \(.*\);/d_set_d_op(\&\1, \2);/' -i Signed-off-by: Nick Piggin --- fs/fat/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/fat/inode.c') diff --git a/fs/fat/inode.c b/fs/fat/inode.c index 8cccfebee180..206351af7c58 100644 --- a/fs/fat/inode.c +++ b/fs/fat/inode.c @@ -750,7 +750,7 @@ static struct dentry *fat_fh_to_dentry(struct super_block *sb, */ result = d_obtain_alias(inode); if (!IS_ERR(result)) - result->d_op = sb->s_root->d_op; + d_set_d_op(result, sb->s_root->d_op); return result; } @@ -800,7 +800,7 @@ static struct dentry *fat_get_parent(struct dentry *child) parent = d_obtain_alias(inode); if (!IS_ERR(parent)) - parent->d_op = sb->s_root->d_op; + d_set_d_op(parent, sb->s_root->d_op); out: unlock_super(sb); -- cgit v1.2.3