bit-spin-locks, as used for dcache hash chains, are not fair. This is not a problem for the dcache hash table as different CPUs are likely to access different entries in the hash table so high contention is not expected. However anonymous dentryies (created by NFSD) all live on a single hash chain "s_anon" and the bitlock on this can be highly contended, resulting in soft-lockup warnings. So introduce a global (fair) spinlock and take it before grabing the bitlock on s_anon. This provides fairness and makes the warnings go away. We could alternately use s_inode_list_lock, or add another spinlock to struct super_block. Suggestions? Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- Dave: I'd guess you would be against using the new s_inode_list_lock for this because it is already highly contended - yes? Is it worth adding another spinlock to 'struct super_block' ? Thanks, NeilBrown fs/dcache.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index 92d5140de851..e83f1ac1540c 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -104,6 +104,8 @@ static unsigned int d_hash_shift __read_mostly; static struct hlist_bl_head *dentry_hashtable __read_mostly; +static DEFINE_SPINLOCK(s_anon_lock); + static inline struct hlist_bl_head *d_hash(const struct dentry *parent, unsigned int hash) { @@ -490,10 +492,14 @@ void __d_drop(struct dentry *dentry) else b = d_hash(dentry->d_parent, dentry->d_name.hash); + if (b == &dentry->d_sb->s_anon) + spin_lock(&s_anon_lock); hlist_bl_lock(b); __hlist_bl_del(&dentry->d_hash); dentry->d_hash.pprev = NULL; hlist_bl_unlock(b); + if (b == &dentry->d_sb->s_anon) + spin_unlock(&s_anon_lock); dentry_rcuwalk_invalidate(dentry); } } @@ -1978,9 +1984,11 @@ static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected) spin_lock(&tmp->d_lock); __d_set_inode_and_type(tmp, inode, add_flags); hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry); + spin_lock(&s_anon_lock); hlist_bl_lock(&tmp->d_sb->s_anon); hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon); hlist_bl_unlock(&tmp->d_sb->s_anon); + spin_unlock(&s_anon_lock); spin_unlock(&tmp->d_lock); spin_unlock(&inode->i_lock); security_d_instantiate(tmp, inode); -- 2.7.0
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