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Subject[PATCH v2 11/35] mm: rcu safe vma freeing
Date
This prepares for speculative page faults looking up and copying vmas
under protection of an rcu read lock, instead of the usual mmap read lock.

Note - it might also be feasible to just use SLAB_TYPESAFE_BY_RCU when
creating the vm_area_cachep, but that's probably too subtle to consider here.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
---
include/linux/mm_types.h | 16 +++++++++++-----
kernel/fork.c | 13 +++++++++++++
2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index e4965a6f34f2..b6678578a729 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -374,12 +374,18 @@ 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, vm_end;

- /* linked list of VM areas per task, sorted by address */
- struct vm_area_struct *vm_next, *vm_prev;
+ /* linked list of VMAs per task, sorted by address */
+ struct vm_area_struct *vm_next, *vm_prev;
+ };
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ struct rcu_head vm_rcu; /* Used for deferred freeing. */
+#endif
+ };

struct rb_node vm_rb;

diff --git a/kernel/fork.c b/kernel/fork.c
index d75a528f7b21..2e5f2e8de31a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -371,10 +371,23 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
return new;
}

+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+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_vma_anon_name(vma);
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ 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)
--
2.20.1
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