diff options
Diffstat (limited to 'include/linux/kernfs.h')
| -rw-r--r-- | include/linux/kernfs.h | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index 2dd9c8df0f4f..13e703f615f7 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -18,6 +18,7 @@ #include <linux/uidgid.h> #include <linux/wait.h> #include <linux/rwsem.h> +#include <linux/cache.h> struct file; struct dentry; @@ -34,6 +35,62 @@ struct kernfs_fs_context; struct kernfs_open_node; struct kernfs_iattrs; +/* + * NR_KERNFS_LOCK_BITS determines size (NR_KERNFS_LOCKS) of hash + * table of locks. + * Having a small hash table would impact scalability, since + * more and more kernfs_node objects will end up using same lock + * and having a very large hash table would waste memory. + * + * At the moment size of hash table of locks is being set based on + * the number of CPUs as follows: + * + * NR_CPU NR_KERNFS_LOCK_BITS NR_KERNFS_LOCKS + * 1 1 2 + * 2-3 2 4 + * 4-7 4 16 + * 8-15 6 64 + * 16-31 8 256 + * 32 and more 10 1024 + * + * The above relation between NR_CPU and number of locks is based + * on some internal experimentation which involved booting qemu + * with different values of smp, performing some sysfs operations + * on all CPUs and observing how increase in number of locks impacts + * completion time of these sysfs operations on each CPU. + */ +#ifdef CONFIG_SMP +#define NR_KERNFS_LOCK_BITS (2 * (ilog2(NR_CPUS < 32 ? NR_CPUS : 32))) +#else +#define NR_KERNFS_LOCK_BITS 1 +#endif + +#define NR_KERNFS_LOCKS (1 << NR_KERNFS_LOCK_BITS) + +/* + * There's one kernfs_open_file for each open file and one kernfs_open_node + * for each kernfs_node with one or more open files. + * + * filp->private_data points to seq_file whose ->private points to + * kernfs_open_file. + * + * kernfs_open_files are chained at kernfs_open_node->files, which is + * protected by kernfs_global_locks.open_file_mutex[i]. + * + * To reduce possible contention in sysfs access, arising due to single + * locks, use an array of locks (e.g. open_file_mutex) and use kernfs_node + * object address as hash keys to get the index of these locks. + * + * Hashed mutexes are safe to use here because operations using these don't + * rely on global exclusion. + * + * In future we intend to replace other global locks with hashed ones as well. + * kernfs_global_locks acts as a holder for all such hash tables. + */ +struct kernfs_global_locks { + struct mutex open_file_mutex[NR_KERNFS_LOCKS]; +}; + enum kernfs_node_type { KERNFS_DIR = 0x0001, KERNFS_FILE = 0x0002, |