vfs: only read fops once in fops_get/put
In do_dentry_open() the usage is:
f->f_op = fops_get(inode->i_fop);
In generated asm the compiler emits 2 reads from inode->i_fop instead of
just one.
This popped up due to false-sharing where loads from that offset end up
bouncing a cacheline during parallel open. While this is going to be fixed,
the spurious load does not need to be there.
This makes do_dentry_open() go down from 1177 to 1154 bytes.
fops_put() is patched to maintain some consistency.
No functional changes.
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c0286d4..696c620 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2553,10 +2553,17 @@ struct super_block *sget(struct file_system_type *type,
struct super_block *sget_dev(struct fs_context *fc, dev_t dev);
/* Alas, no aliases. Too much hassle with bringing module.h everywhere */
-#define fops_get(fops) \
- (((fops) && try_module_get((fops)->owner) ? (fops) : NULL))
-#define fops_put(fops) \
- do { if (fops) module_put((fops)->owner); } while(0)
+#define fops_get(fops) ({ \
+ const struct file_operations *_fops = (fops); \
+ (((_fops) && try_module_get((_fops)->owner) ? (_fops) : NULL)); \
+})
+
+#define fops_put(fops) ({ \
+ const struct file_operations *_fops = (fops); \
+ if (_fops) \
+ module_put((_fops)->owner); \
+})
+
/*
* This one is to be used *ONLY* from ->open() instances.
* fops must be non-NULL, pinned down *and* module dependencies
