mm/vmacache.c

   1 /*
   2  * Copyright (C) 2014 Davidlohr Bueso.
   3  */
   4 #include <linux/sched.h>
   5 #include <linux/mm.h>
   6 #include <linux/vmacache.h>
   7
   8 /*
   9  * Flush vma caches for threads that share a given mm.
  10  *
  11  * The operation is safe because the caller holds the mmap_sem
  12  * exclusively and other threads accessing the vma cache will
  13  * have mmap_sem held at least for read, so no extra locking
  14  * is required to maintain the vma cache.
  15  */
  16 void vmacache_flush_all(struct mm_struct *mm)
  17 {
  18         struct task_struct *g, *p;
  19
  20         count_vm_vmacache_event(VMACACHE_FULL_FLUSHES);
  21
  22         /*
  23          * Single threaded tasks need not iterate the entire
  24          * list of process. We can avoid the flushing as well
  25          * since the mm's seqnum was increased and don't have
  26          * to worry about other threads' seqnum. Current's
  27          * flush will occur upon the next lookup.
  28          */
  29         if (atomic_read(&mm->mm_users) == 1)
  30                 return;
  31
  32         rcu_read_lock();
  33         for_each_process_thread(g, p) {
  34                 /*
  35                  * Only flush the vmacache pointers as the
  36                  * mm seqnum is already set and curr's will
  37                  * be set upon invalidation when the next
  38                  * lookup is done.
  39                  */
  40                 if (mm == p->mm)
  41                         vmacache_flush(p);
  42         }
  43         rcu_read_unlock();
  44 }
  45
  46 /*
  47  * This task may be accessing a foreign mm via (for example)
  48  * get_user_pages()->find_vma().  The vmacache is task-local and this
  49  * task's vmacache pertains to a different mm (ie, its own).  There is
  50  * nothing we can do here.
  51  *
  52  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  53  * That kernel thread's vmacache is not applicable to this mm.
  54  */
  55 static bool vmacache_valid_mm(struct mm_struct *mm)
  56 {
  57         return current->mm == mm && !(current->flags & PF_KTHREAD);
  58 }
  59
  60 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  61 {
  62         if (vmacache_valid_mm(newvma->vm_mm))
  63                 current->vmacache[VMACACHE_HASH(addr)] = newvma;
  64 }
  65
  66 static bool vmacache_valid(struct mm_struct *mm)
  67 {
  68         struct task_struct *curr;
  69
  70         if (!vmacache_valid_mm(mm))
  71                 return false;
  72
  73         curr = current;
  74         if (mm->vmacache_seqnum != curr->vmacache_seqnum) {
  75                 /*
  76                  * First attempt will always be invalid, initialize
  77                  * the new cache for this task here.
  78                  */
  79                 curr->vmacache_seqnum = mm->vmacache_seqnum;
  80                 vmacache_flush(curr);
  81                 return false;
  82         }
  83         return true;
  84 }
  85
  86 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  87 {
  88         int i;
  89
  90         if (!vmacache_valid(mm))
  91                 return NULL;
  92
  93         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  94
  95         for (i = 0; i < VMACACHE_SIZE; i++) {
  96                 struct vm_area_struct *vma = current->vmacache[i];
  97
  98                 if (!vma)
  99                         continue;
 100                 if (WARN_ON_ONCE(vma->vm_mm != mm))
 101                         break;
 102                 if (vma->vm_start <= addr && vma->vm_end > addr) {
 103                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 104                         return vma;
 105                 }
 106         }
 107
 108         return NULL;
 109 }
 110
 111 #ifndef CONFIG_MMU
 112 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
 113                                            unsigned long start,
 114                                            unsigned long end)
 115 {
 116         int i;
 117
 118         if (!vmacache_valid(mm))
 119                 return NULL;
 120
 121         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 122
 123         for (i = 0; i < VMACACHE_SIZE; i++) {
 124                 struct vm_area_struct *vma = current->vmacache[i];
 125
 126                 if (vma && vma->vm_start == start && vma->vm_end == end) {
 127                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 128                         return vma;
 129                 }
 130         }
 131
 132         return NULL;
 133 }
 134 #endif