Commit a55d1cbd authored Aug 22, 2024 by Christian Brauner

fs: switch f_iocb_flags and f_ra

Now that we shrank struct file by 24 bytes we still have a 4 byte hole.
If we move struct file_ra_state into the union and f_iocb_flags out of
the union we close that whole and bring down struct file to 192 bytes.
Which means struct file is 3 cachelines and we managed to shrink it by
40 bytes this cycle.

I've tried to audit all codepaths that use f_ra and none of them seem to
rely on it in file->f_op->release() and never have since commit
1da177e4 ("Linux-2.6.12-rc2").

Link: https://lore.kernel.org/r/20240823-luftdicht-berappen-d69a2166a0db@brauner


Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

parent 1934b212

include/linux/fs.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -999,9 +999,9 @@ struct file {
		struct callback_head f_task_work;
		/* fput() must use workqueue (most kernel threads). */
		struct llist_node f_llist;
		unsigned int f_iocb_flags;
		/* Invalid after last fput(). */
		struct file_ra_state f_ra;
		};

		/*
		* Protects f_ep, f_flags.
		* Must not be taken from IRQ context.
		@@ -1012,9 +1012,9 @@ struct file {
		struct mutex f_pos_lock;
		loff_t f_pos;
		unsigned int f_flags;
		unsigned int f_iocb_flags;
		struct fown_struct *f_owner;
		const struct cred *f_cred;
		struct file_ra_state f_ra;
		struct path f_path;
		struct inode f_inode; / cached value */
		const struct file_operations *f_op;