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authorAl Viro <viro@zeniv.linux.org.uk>2016-04-15 02:42:04 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2016-05-02 19:49:27 -0400
commit94bdd655caba2080ae81d83d756d325abdffcb9f (patch)
treeaff6bb4952f700479d7fc6e61b24c106d3ab3262 /include/linux/dcache.h
parent84e710da2a1dfacfc87f604869a4d22df91ce6cd (diff)
parallel lookups machinery, part 3
We will need to be able to check if there is an in-lookup dentry with matching parent/name. Right now it's impossible, but as soon as start locking directories shared such beasts will appear. Add a secondary hash for locating those. Hash chains go through the same space where d_alias will be once it's not in-lookup anymore. Search is done under the same bitlock we use for modifications - with the primary hash we can rely on d_rehash() into the wrong chain being the worst that could happen, but here the pointers are buggered once it's removed from the chain. On the other hand, the chains are not going to be long and normally we'll end up adding to the chain anyway. That allows us to avoid bothering with ->d_lock when doing the comparisons - everything is stable until removed from chain. New helper: d_alloc_parallel(). Right now it allocates, verifies that no hashed and in-lookup matches exist and adds to in-lookup hash. Returns ERR_PTR() for error, hashed match (in the unlikely case it's been found) or new dentry. In-lookup matches trigger BUG() for now; that will change in the next commit when we introduce waiting for ongoing lookup to finish. Note that in-lookup matches won't be possible until we actually go for shared locking. lookup_slow() switched to use of d_alloc_parallel(). Again, these commits are separated only for making it easier to review. All this machinery will start doing something useful only when we go for shared locking; it's just that the combination is too large for my taste. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux/dcache.h')
-rw-r--r--include/linux/dcache.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 9a7aa890b642..3eea562f5f27 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -131,6 +131,7 @@ struct dentry {
*/
union {
struct hlist_node d_alias; /* inode alias list */
+ struct hlist_bl_node d_in_lookup_hash; /* only for in-lookup ones */
struct rcu_head d_rcu;
} d_u;
};
@@ -250,6 +251,7 @@ extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op
/* allocate/de-allocate */
extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
+extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *);
extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
extern struct dentry * d_exact_alias(struct dentry *, struct inode *);