mm: rcu safe VMA freeing

This prepares for page faults handling under VMA lock, looking up VMAs
under protection of an rcu read lock, instead of the usual mmap read lock.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 500e536796ca4ade1721e1ca82f4b09926e3c8a4..eba3987b22d8ad8166c45105f9ac5961a80d14ab 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -444,9 +444,16 @@ struct anon_vma_name {
 struct vm_area_struct {
        /* The first cache line has the info for VMA tree walking. */
 
-       unsigned long vm_start;         /* Our start address within vm_mm. */
-       unsigned long vm_end;           /* The first byte after our end address
-                                          within vm_mm. */
+       union {
+               struct {
+                       /* VMA covers [vm_start; vm_end) addresses within mm */
+                       unsigned long vm_start;
+                       unsigned long vm_end;
+               };
+#ifdef CONFIG_PER_VMA_LOCK
+               struct rcu_head vm_rcu; /* Used for deferred freeing. */
+#endif
+       };
 
        struct mm_struct *vm_mm;        /* The address space we belong to. */
 

diff --git a/kernel/fork.c b/kernel/fork.c
index f8ce1fc21378502272081b2911d91e4040656d60..a4993ac1613b4ace33f1ec6d8e83d9f2a616546b 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -479,10 +479,23 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
        return new;
 }
 
+#ifdef CONFIG_PER_VMA_LOCK
+static void __vm_area_free(struct rcu_head *head)
+{
+       struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
+                                                 vm_rcu);
+       kmem_cache_free(vm_area_cachep, vma);
+}
+#endif
+
 void vm_area_free(struct vm_area_struct *vma)
 {
        free_anon_vma_name(vma);
+#ifdef CONFIG_PER_VMA_LOCK
+       call_rcu(&vma->vm_rcu, __vm_area_free);
+#else
        kmem_cache_free(vm_area_cachep, vma);
+#endif
 }
 
 static void account_kernel_stack(struct task_struct *tsk, int account)