From 1a0a397e41cb1bf70cfe45fd0eeff08c7c501ec0 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Fri, 14 Feb 2014 17:35:37 -0500 Subject: dcache: d_obtain_alias callers don't all want DISCONNECTED There are a few d_obtain_alias callers that are using it to get the root of a filesystem which may already have an alias somewhere else. This is not the same as the filehandle-lookup case, and none of them actually need DCACHE_DISCONNECTED set. It isn't really a serious problem, but it would really be clearer if we reserved DCACHE_DISCONNECTED for those cases where it's actually needed. In the btrfs case this was causing a spurious printk from nfsd/nfsfh.c:fh_verify when it found an unexpected DCACHE_DISCONNECTED dentry. Josef worked around this by unsetting DCACHE_DISCONNECTED manually in 3a0dfa6a12e "Btrfs: unset DCACHE_DISCONNECTED when mounting default subvol", and this replaces that workaround. Cc: Josef Bacik Signed-off-by: J. Bruce Fields Signed-off-by: Al Viro --- include/linux/dcache.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/dcache.h') diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 3c7ec327ebd2..e4ae2ad48d07 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -249,6 +249,7 @@ 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_find_any_alias(struct inode *inode); extern struct dentry * d_obtain_alias(struct inode *); +extern struct dentry * d_obtain_root(struct inode *); extern void shrink_dcache_sb(struct super_block *); extern void shrink_dcache_parent(struct dentry *); extern void shrink_dcache_for_umount(struct super_block *); -- cgit v1.2.3 From 9226b5b440f2b4fbb3b797f3cb74a9a627220660 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 14 Sep 2014 17:28:32 -0700 Subject: vfs: avoid non-forwarding large load after small store in path lookup The performance regression that Josef Bacik reported in the pathname lookup (see commit 99d263d4c5b2 "vfs: fix bad hashing of dentries") made me look at performance stability of the dcache code, just to verify that the problem was actually fixed. That turned up a few other problems in this area. There are a few cases where we exit RCU lookup mode and go to the slow serializing case when we shouldn't, Al has fixed those and they'll come in with the next VFS pull. But my performance verification also shows that link_path_walk() turns out to have a very unfortunate 32-bit store of the length and hash of the name we look up, followed by a 64-bit read of the combined hash_len field. That screws up the processor store to load forwarding, causing an unnecessary hickup in this critical routine. It's caused by the ugly calling convention for the "hash_name()" function, and easily fixed by just making hash_name() fill in the whole 'struct qstr' rather than passing it a pointer to just the hash value. With that, the profile for this function looks much smoother. Signed-off-by: Linus Torvalds --- fs/namei.c | 19 ++++++++++--------- include/linux/dcache.h | 1 + 2 files changed, 11 insertions(+), 9 deletions(-) (limited to 'include/linux/dcache.h') diff --git a/fs/namei.c b/fs/namei.c index 229235862e50..2be5120b81b3 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1669,13 +1669,14 @@ EXPORT_SYMBOL(full_name_hash); /* * Calculate the length and hash of the path component, and - * return the length of the component; + * fill in the qstr. return the "len" as the result. */ -static inline unsigned long hash_name(const char *name, unsigned int *hashp) +static inline unsigned long hash_name(const char *name, struct qstr *res) { unsigned long a, b, adata, bdata, mask, hash, len; const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; + res->name = name; hash = a = 0; len = -sizeof(unsigned long); do { @@ -1691,9 +1692,10 @@ static inline unsigned long hash_name(const char *name, unsigned int *hashp) mask = create_zero_mask(adata | bdata); hash += a & zero_bytemask(mask); - *hashp = fold_hash(hash); + len += find_zero(mask); + res->hash_len = hashlen_create(fold_hash(hash), len); - return len + find_zero(mask); + return len; } #else @@ -1711,18 +1713,19 @@ EXPORT_SYMBOL(full_name_hash); * We know there's a real path component here of at least * one character. */ -static inline unsigned long hash_name(const char *name, unsigned int *hashp) +static inline long hash_name(const char *name, struct qstr *res) { unsigned long hash = init_name_hash(); unsigned long len = 0, c; + res->name = name; c = (unsigned char)*name; do { len++; hash = partial_name_hash(c, hash); c = (unsigned char)name[len]; } while (c && c != '/'); - *hashp = end_name_hash(hash); + res->hash_len = hashlen_create(end_name_hash(hash), len); return len; } @@ -1756,9 +1759,7 @@ static int link_path_walk(const char *name, struct nameidata *nd) if (err) break; - len = hash_name(name, &this.hash); - this.name = name; - this.len = len; + len = hash_name(name, &this); type = LAST_NORM; if (name[0] == '.') switch (len) { diff --git a/include/linux/dcache.h b/include/linux/dcache.h index e4ae2ad48d07..75a227cc7ce2 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -55,6 +55,7 @@ struct qstr { #define QSTR_INIT(n,l) { { { .len = l } }, .name = n } #define hashlen_hash(hashlen) ((u32) (hashlen)) #define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) +#define hashlen_create(hash,len) (((u64)(len)<<32)|(u32)(hash)) struct dentry_stat_t { long nr_dentry; -- cgit v1.2.3