mm/vmacache.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2014 Davidlohr Bueso.
   4  */
   5 #include <linux/sched/signal.h>
   6 #include <linux/sched/task.h>
   7 #include <linux/mm.h>
   8 #include <linux/vmacache.h>
   9
  10 /*
  11  * Hash based on the pmd of addr if configured with MMU, which provides a good
  12  * hit rate for workloads with spatial locality.  Otherwise, use pages.
  13  */
  14 #ifdef CONFIG_MMU
  15 #define VMACACHE_SHIFT  PMD_SHIFT
  16 #else
  17 #define VMACACHE_SHIFT  PAGE_SHIFT
  18 #endif
  19 #define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
  20
  21 /*
  22  * This task may be accessing a foreign mm via (for example)
  23  * get_user_pages()->find_vma().  The vmacache is task-local and this
  24  * task's vmacache pertains to a different mm (ie, its own).  There is
  25  * nothing we can do here.
  26  *
  27  * Also handle the case where a kernel thread has adopted this mm via
  28  * kthread_use_mm(). That kernel thread's vmacache is not applicable to this mm.
  29  */
  30 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  31 {
  32         return current->mm == mm && !(current->flags & PF_KTHREAD);
  33 }
  34
  35 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  36 {
  37         if (vmacache_valid_mm(newvma->vm_mm))
  38                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
  39 }
  40
  41 static bool vmacache_valid(struct mm_struct *mm)
  42 {
  43         struct task_struct *curr;
  44
  45         if (!vmacache_valid_mm(mm))
  46                 return false;
  47
  48         curr = current;
  49         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
  50                 /*
  51                  * First attempt will always be invalid, initialize
  52                  * the new cache for this task here.
  53                  */
  54                 curr->vmacache.seqnum = mm->vmacache_seqnum;
  55                 vmacache_flush(curr);
  56                 return false;
  57         }
  58         return true;
  59 }
  60
  61 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  62 {
  63         int idx = VMACACHE_HASH(addr);
  64         int i;
  65
  66         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  67
  68         if (!vmacache_valid(mm))
  69                 return NULL;
  70
  71         for (i = 0; i < VMACACHE_SIZE; i++) {
  72                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
  73
  74                 if (vma) {
  75 #ifdef CONFIG_DEBUG_VM_VMACACHE
  76                         if (WARN_ON_ONCE(vma->vm_mm != mm))
  77                                 break;
  78 #endif
  79                         if (vma->vm_start <= addr && vma->vm_end > addr) {
  80                                 count_vm_vmacache_event(VMACACHE_FIND_HITS);
  81                                 return vma;
  82                         }
  83                 }
  84                 if (++idx == VMACACHE_SIZE)
  85                         idx = 0;
  86         }
  87
  88         return NULL;
  89 }
  90
  91 #ifndef CONFIG_MMU
  92 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  93                                            unsigned long start,
  94                                            unsigned long end)
  95 {
  96         int idx = VMACACHE_HASH(start);
  97         int i;
  98
  99         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 100
 101         if (!vmacache_valid(mm))
 102                 return NULL;
 103
 104         for (i = 0; i < VMACACHE_SIZE; i++) {
 105                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
 106
 107                 if (vma && vma->vm_start == start && vma->vm_end == end) {
 108                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 109                         return vma;
 110                 }
 111                 if (++idx == VMACACHE_SIZE)
 112                         idx = 0;
 113         }
 114
 115         return NULL;
 116 }
 117 #endif