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fs: pack struct file

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Now that we shrunk struct file to 192 bytes aka 3 cachelines reorder
struct file to not leave any holes or have members cross cachelines.

Add a short comment to each of the fields and mark the cachelines.
It's possible that we may have to tweak this based on profiling in the
future. So far I had Jens test this comparing io_uring with non-fixed
and fixed files and it improved performance. The layout is a combination
of Jens' and my changes.

Link: https: //lore.kernel.org/r/20240824-peinigen-hocken-7384b977c643@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-08-23 21:06:58 +02:00
parent a55d1cbd17
commit c0390d5411
1 changed files with 51 additions and 40 deletions
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91
include/linux/fs.h
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@ -987,52 +987,63 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
index < ra->start + ra->size);
}
/*
* f_{lock,count,pos_lock} members can be highly contended and share
* the same cacheline. f_{lock,mode} are very frequently used together
* and so share the same cacheline as well. The read-mostly
* f_{path,inode,op} are kept on a separate cacheline.
/**
* struct file - Represents a file
* @f_count: reference count
* @f_lock: Protects f_ep, f_flags. Must not be taken from IRQ context.
* @f_mode: FMODE_* flags often used in hotpaths
* @f_op: file operations
* @f_mapping: Contents of a cacheable, mappable object.
* @private_data: filesystem or driver specific data
* @f_inode: cached inode
* @f_flags: file flags
* @f_iocb_flags: iocb flags
* @f_cred: stashed credentials of creator/opener
* @f_path: path of the file
* @f_pos_lock: lock protecting file position
* @f_pos: file position
* @f_version: file version
* @f_security: LSM security context of this file
* @f_owner: file owner
* @f_wb_err: writeback error
* @f_sb_err: per sb writeback errors
* @f_ep: link of all epoll hooks for this file
* @f_task_work: task work entry point
* @f_llist: work queue entrypoint
* @f_ra: file's readahead state
*/
struct file {
atomic_long_t f_count;
spinlock_t f_lock;
fmode_t f_mode;
const struct file_operations *f_op;
struct address_space *f_mapping;
void *private_data;
struct inode *f_inode;
unsigned int f_flags;
unsigned int f_iocb_flags;
const struct cred *f_cred;
/* --- cacheline 1 boundary (64 bytes) --- */
struct path f_path;
struct mutex f_pos_lock;
loff_t f_pos;
u64 f_version;
/* --- cacheline 2 boundary (128 bytes) --- */
#ifdef CONFIG_SECURITY
void *f_security;
#endif
struct fown_struct *f_owner;
errseq_t f_wb_err;
errseq_t f_sb_err;
#ifdef CONFIG_EPOLL
struct hlist_head *f_ep;
#endif
union {
/* fput() uses task work when closing and freeing file (default). */
struct callback_head f_task_work;
/* fput() must use workqueue (most kernel threads). */
struct callback_head f_task_work;
struct llist_node f_llist;
/* Invalid after last fput(). */
struct file_ra_state f_ra;
};
/*
* Protects f_ep, f_flags.
* Must not be taken from IRQ context.
*/
spinlock_t f_lock;
fmode_t f_mode;
atomic_long_t f_count;
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 path f_path;
struct inode *f_inode; /* cached value */
const struct file_operations *f_op;
u64 f_version;
#ifdef CONFIG_SECURITY
void *f_security;
#endif
/* needed for tty driver, and maybe others */
void *private_data;
#ifdef CONFIG_EPOLL
/* Used by fs/eventpoll.c to link all the hooks to this file */
struct hlist_head *f_ep;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
errseq_t f_wb_err;
errseq_t f_sb_err; /* for syncfs */
/* --- cacheline 3 boundary (192 bytes) --- */
} __randomize_layout
__attribute__((aligned(4))); /* lest something weird decides that 2 is OK */