LXR linux/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 */
  16void 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 */
  55static inline bool vmacache_valid_mm(struct mm_struct *mm)
  56{
  57        return current->mm == mm && !(current->flags & PF_KTHREAD);
  58}
  59
  60void 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
  66static 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
  86struct 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
 112struct 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
 135