On Thu, 2024-08-22 at 16:14 +0200, Christian Brauner wrote:
> Now that we shrank struct file by 24 bytes we still have a 4 byte hole.
> Move f_version into the union and f_iocb_flags out of the union to fill
> that hole and shrink struct file by another 4 bytes. This brings struct
> file to 200 bytes down from 232 bytes.
>
> I've tried to audit all codepaths that use f_version and none of them
> rely on it in file->f_op->release() and never have since commit
> 1da177e4c3f4 ("Linux-2.6.12-rc2").
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
> ---
> struct file {
> union {
> struct callback_head f_task_work; /* 0 16 */
> struct llist_node f_llist; /* 0 8 */
> u64 f_version; /* 0 8 */
> }; /* 0 16 */
> spinlock_t f_lock; /* 16 4 */
> fmode_t f_mode; /* 20 4 */
> atomic_long_t f_count; /* 24 8 */
> struct mutex f_pos_lock; /* 32 32 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> loff_t f_pos; /* 64 8 */
> unsigned int f_flags; /* 72 4 */
> unsigned int f_iocb_flags; /* 76 4 */
> struct fown_struct * f_owner; /* 80 8 */
> const struct cred * f_cred; /* 88 8 */
> struct file_ra_state f_ra; /* 96 32 */
> /* --- cacheline 2 boundary (128 bytes) --- */
> struct path f_path; /* 128 16 */
> struct inode * f_inode; /* 144 8 */
> const struct file_operations * f_op; /* 152 8 */
> void * f_security; /* 160 8 */
> void * private_data; /* 168 8 */
> struct hlist_head * f_ep; /* 176 8 */
> struct address_space * f_mapping; /* 184 8 */
> /* --- cacheline 3 boundary (192 bytes) --- */
> errseq_t f_wb_err; /* 192 4 */
> errseq_t f_sb_err; /* 196 4 */
>
> /* size: 200, cachelines: 4, members: 20 */
> /* last cacheline: 8 bytes */
> };
> ---
> include/linux/fs.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 7eb4f706d59f..7a2994405e8e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -998,9 +998,8 @@ 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;
> + u64 f_version;
> };
> -
> /*
> * Protects f_ep, f_flags.
> * Must not be taken from IRQ context.
> @@ -1011,6 +1010,7 @@ 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;
> @@ -1018,7 +1018,6 @@ struct file {
> struct inode *f_inode; /* cached value */
> const struct file_operations *f_op;
>
> - u64 f_version;
> #ifdef CONFIG_SECURITY
> void *f_security;
> #endif
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
