From 5370b43e4bcf60049bfd44db83ba8d2ec43d0152 Mon Sep 17 00:00:00 2001 From: Mateusz Guzik Date: Wed, 19 Mar 2025 22:58:01 +0100 Subject: fs: reduce work in fdget_pos() 1. predict the file was found 2. explicitly compare the ref to "one", ignoring the dead zone The latter arguably improves the behavior to begin with. Suppose the count turned bad -- the previously used ref routine is going to check for it and return 0, indicating the count does not necessitate taking ->f_pos_lock. But there very well may be several users. i.e. not paying for special-casing the dead zone improves semantics. While here spell out each condition in a dedicated if statement. This has no effect on generated code. Sizes are as follows (in bytes; gcc 13, x86-64): stock: 321 likely(): 298 likely()+ref: 280 Signed-off-by: Mateusz Guzik Link: https://lore.kernel.org/r/20250319215801.1870660-1-mjguzik@gmail.com Signed-off-by: Christian Brauner --- fs/file.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'fs/file.c') diff --git a/fs/file.c b/fs/file.c index 3fef798b96e5..134274446bf6 100644 --- a/fs/file.c +++ b/fs/file.c @@ -1183,8 +1183,13 @@ struct fd fdget_raw(unsigned int fd) */ static inline bool file_needs_f_pos_lock(struct file *file) { - return (file->f_mode & FMODE_ATOMIC_POS) && - (file_count(file) > 1 || file->f_op->iterate_shared); + if (!(file->f_mode & FMODE_ATOMIC_POS)) + return false; + if (__file_ref_read_raw(&file->f_ref) != FILE_REF_ONEREF) + return true; + if (file->f_op->iterate_shared) + return true; + return false; } struct fd fdget_pos(unsigned int fd) @@ -1192,7 +1197,7 @@ struct fd fdget_pos(unsigned int fd) struct fd f = fdget(fd); struct file *file = fd_file(f); - if (file && file_needs_f_pos_lock(file)) { + if (likely(file) && file_needs_f_pos_lock(file)) { f.word |= FDPUT_POS_UNLOCK; mutex_lock(&file->f_pos_lock); } -- cgit