mm: per-thread vma caching

[firefly-linux-kernel-4.4.55.git] / mm / vmacache.c

diff --git a/mm/vmacache.c b/mm/vmacache.c
new file mode 100644 (file)
index 0000000..d4224b3
--- /dev/null
+++ b/mm/vmacache.c
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2014 Davidlohr Bueso.
+ */
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/vmacache.h>
+
+/*
+ * Flush vma caches for threads that share a given mm.
+ *
+ * The operation is safe because the caller holds the mmap_sem
+ * exclusively and other threads accessing the vma cache will
+ * have mmap_sem held at least for read, so no extra locking
+ * is required to maintain the vma cache.
+ */
+void vmacache_flush_all(struct mm_struct *mm)
+{
+       struct task_struct *g, *p;
+
+       rcu_read_lock();
+       for_each_process_thread(g, p) {
+               /*
+                * Only flush the vmacache pointers as the
+                * mm seqnum is already set and curr's will
+                * be set upon invalidation when the next
+                * lookup is done.
+                */
+               if (mm == p->mm)
+                       vmacache_flush(p);
+       }
+       rcu_read_unlock();
+}
+
+/*
+ * This task may be accessing a foreign mm via (for example)
+ * get_user_pages()->find_vma().  The vmacache is task-local and this
+ * task's vmacache pertains to a different mm (ie, its own).  There is
+ * nothing we can do here.
+ *
+ * Also handle the case where a kernel thread has adopted this mm via use_mm().
+ * That kernel thread's vmacache is not applicable to this mm.
+ */
+static bool vmacache_valid_mm(struct mm_struct *mm)
+{
+       return current->mm == mm && !(current->flags & PF_KTHREAD);
+}
+
+void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
+{
+       if (vmacache_valid_mm(newvma->vm_mm))
+               current->vmacache[VMACACHE_HASH(addr)] = newvma;
+}
+
+static bool vmacache_valid(struct mm_struct *mm)
+{
+       struct task_struct *curr;
+
+       if (!vmacache_valid_mm(mm))
+               return false;
+
+       curr = current;
+       if (mm->vmacache_seqnum != curr->vmacache_seqnum) {
+               /*
+                * First attempt will always be invalid, initialize
+                * the new cache for this task here.
+                */
+               curr->vmacache_seqnum = mm->vmacache_seqnum;
+               vmacache_flush(curr);
+               return false;
+       }
+       return true;
+}
+
+struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
+{
+       int i;
+
+       if (!vmacache_valid(mm))
+               return NULL;
+
+       for (i = 0; i < VMACACHE_SIZE; i++) {
+               struct vm_area_struct *vma = current->vmacache[i];
+
+               if (vma && vma->vm_start <= addr && vma->vm_end > addr) {
+                       BUG_ON(vma->vm_mm != mm);
+                       return vma;
+               }
+       }
+
+       return NULL;
+}
+
+#ifndef CONFIG_MMU
+struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
+                                          unsigned long start,
+                                          unsigned long end)
+{
+       int i;
+
+       if (!vmacache_valid(mm))
+               return NULL;
+
+       for (i = 0; i < VMACACHE_SIZE; i++) {
+               struct vm_area_struct *vma = current->vmacache[i];
+
+               if (vma && vma->vm_start == start && vma->vm_end == end)
+                       return vma;
+       }
+
+       return NULL;
+}
+#endif