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author | Linus Torvalds <torvalds@linux-foundation.org> | 2024-06-10 20:47:06 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2024-06-19 21:34:34 +0200 |
commit | e60cc61153e61e4e38bd983492df9959e82ae4dc (patch) | |
tree | c3e9b33a0ad49b111aa0f9a13fe43ec8c04a0894 /fs/dcache.c | |
parent | Linux 6.10-rc4 (diff) | |
download | linux-e60cc61153e61e4e38bd983492df9959e82ae4dc.tar.xz linux-e60cc61153e61e4e38bd983492df9959e82ae4dc.zip |
vfs: dcache: move hashlen_hash() from callers into d_hash()
Both __d_lookup_rcu() and __d_lookup_rcu_op_compare() have the full
'name_hash' value of the qstr that they want to look up, and mask it off
to just the low 32-bit hash before calling down to d_hash().
Other callers just load the 32-bit hash and pass it as the argument.
If we move the masking into d_hash() itself, it simplifies the two
callers that currently do the masking, and is a no-op for the other
cases. It doesn't actually change the generated code since the compiler
will inline d_hash() and see that the end result is the same.
[ Technically, since the parse tree changes, the code generation may not
be 100% the same, and for me on x86-64, this does result in gcc
switching the operands around for one 'cmpl' instruction. So not
necessarily the exact same code generation, but equivalent ]
However, this does encapsulate the 'd_hash()' operation more, and makes
the shift operation in particular be a "shift 32 bits right, return full
word". Which matches the instruction semantics on both x86-64 and arm64
better, since a 32-bit shift will clear the upper bits.
That makes the next step of introducing a "shift by runtime constant"
more obvious and generates the shift with no extraneous type masking.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/dcache.c')
-rw-r--r-- | fs/dcache.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 407095188f83..8b4382f5c99d 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -100,9 +100,9 @@ static unsigned int d_hash_shift __ro_after_init; static struct hlist_bl_head *dentry_hashtable __ro_after_init; -static inline struct hlist_bl_head *d_hash(unsigned int hash) +static inline struct hlist_bl_head *d_hash(unsigned long hashlen) { - return dentry_hashtable + (hash >> d_hash_shift); + return dentry_hashtable + ((u32)hashlen >> d_hash_shift); } #define IN_LOOKUP_SHIFT 10 @@ -2104,7 +2104,7 @@ static noinline struct dentry *__d_lookup_rcu_op_compare( unsigned *seqp) { u64 hashlen = name->hash_len; - struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen)); + struct hlist_bl_head *b = d_hash(hashlen); struct hlist_bl_node *node; struct dentry *dentry; @@ -2171,7 +2171,7 @@ struct dentry *__d_lookup_rcu(const struct dentry *parent, { u64 hashlen = name->hash_len; const unsigned char *str = name->name; - struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen)); + struct hlist_bl_head *b = d_hash(hashlen); struct hlist_bl_node *node; struct dentry *dentry; |