2 files changed, 29 insertions, 9 deletions

diff --git a/include/linux/file.h b/include/linux/file.h
index 9901b850f2e..9f7c2513866 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -10,6 +10,7 @@
 #include <linux/compiler.h>
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
+#include <linux/types.h>
 
 /*
  * The default fd array needs to be at least BITS_PER_LONG,
@@ -17,10 +18,22 @@
  */
 #define NR_OPEN_DEFAULT BITS_PER_LONG
 
+/*
+ * The embedded_fd_set is a small fd_set,
+ * suitable for most tasks (which open <= BITS_PER_LONG files)
+ */
+struct embedded_fd_set {
+        unsigned long fds_bits[1];
+};
+
+/*
+ * More than this number of fds: we use a separately allocated fd_set
+ */
+#define EMBEDDED_FD_SET_SIZE (BITS_PER_BYTE * sizeof(struct embedded_fd_set))
+
 struct fdtable {
         unsigned int max_fds;
         int max_fdset;
-        int next_fd;
         struct file ** fd;      /* current fd array */
         fd_set *close_on_exec;
         fd_set *open_fds;
@@ -33,13 +46,20 @@ struct fdtable {
  * Open file table structure
  */
 struct files_struct {
+  /*
+   * read mostly part
+   */
         atomic_t count;
         struct fdtable *fdt;
         struct fdtable fdtab;
-        fd_set close_on_exec_init;
-        fd_set open_fds_init;
+  /*
+   * written part on a separate cache line in SMP
+   */
+        spinlock_t file_lock ____cacheline_aligned_in_smp;
+        int next_fd;
+        struct embedded_fd_set close_on_exec_init;
+        struct embedded_fd_set open_fds_init;
         struct file * fd_array[NR_OPEN_DEFAULT];
-        spinlock_t file_lock;     /* Protects concurrent writers.  Nests inside tsk->alloc_lock */
 };
 
 #define files_fdtable(files) (rcu_dereference((files)->fdt))
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index dcfd2ecccb5..92146f3b742 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -7,11 +7,10 @@
 #define INIT_FDTABLE \
 {                                                       \
         .max_fds        = NR_OPEN_DEFAULT,              \
-        .max_fdset      = __FD_SETSIZE,                 \
-        .next_fd        = 0,                            \
+        .max_fdset      = EMBEDDED_FD_SET_SIZE,         \
         .fd             = &init_files.fd_array[0],      \
-        .close_on_exec  = &init_files.close_on_exec_init, \
-        .open_fds       = &init_files.open_fds_init,    \
+        .close_on_exec  = (fd_set *)&init_files.close_on_exec_init, \
+        .open_fds       = (fd_set *)&init_files.open_fds_init,  \
         .rcu            = RCU_HEAD_INIT,                \
         .free_files     = NULL,                         \
         .next           = NULL,                         \
@@ -20,9 +19,10 @@
 #define INIT_FILES \
 {                                                       \
         .count          = ATOMIC_INIT(1),               \
-        .file_lock      = SPIN_LOCK_UNLOCKED,           \
         .fdt            = &init_files.fdtab,            \
         .fdtab          = INIT_FDTABLE,                 \
+        .file_lock      = SPIN_LOCK_UNLOCKED,           \
+        .next_fd        = 0,                            \
         .close_on_exec_init = { { 0, } },               \
         .open_fds_init  = { { 0, } },                   \
         .fd_array       = { NULL, }                     \