[PATCH] files: files struct with RCU
Patch to eliminate struct files_struct.file_lock spinlock on the reader side
and use rcu refcounting rcuref_xxx api for the f_count refcounter. The
updates to the fdtable are done by allocating a new fdtable structure and
setting files->fdt to point to the new structure. The fdtable structure is
protected by RCU thereby allowing lock-free lookup. For fd arrays/sets that
are vmalloced, we use keventd to free them since RCU callbacks can't sleep. A
global list of fdtable to be freed is not scalable, so we use a per-cpu list.
If keventd is already handling the current cpu's work, we use a timer to defer
queueing of that work.
Since the last publication, this patch has been re-written to avoid using
explicit memory barriers and use rcu_assign_pointer(), rcu_dereference()
premitives instead. This required that the fd information is kept in a
separate structure (fdtable) and updated atomically.
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 94aefa5..68ab5f2 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -2,6 +2,7 @@
#define _LINUX__INIT_TASK_H
#include <linux/file.h>
+#include <linux/rcupdate.h>
#define INIT_FDTABLE \
{ \
@@ -11,12 +12,16 @@
.fd = &init_files.fd_array[0], \
.close_on_exec = &init_files.close_on_exec_init, \
.open_fds = &init_files.open_fds_init, \
+ .rcu = RCU_HEAD_INIT, \
+ .free_files = NULL, \
+ .next = NULL, \
}
#define INIT_FILES \
{ \
.count = ATOMIC_INIT(1), \
.file_lock = SPIN_LOCK_UNLOCKED, \
+ .fdt = &init_files.fdtab, \
.fdtab = INIT_FDTABLE, \
.close_on_exec_init = { { 0, } }, \
.open_fds_init = { { 0, } }, \