the-tree/mm/vmacache.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * Copyright (C) 2014 Davidlohr Bueso.
0004  */
0005 #include <linux/sched/signal.h>
0006 #include <linux/sched/task.h>
0007 #include <linux/mm.h>
0008 #include <linux/vmacache.h>
0009
0010 /*
0011  * Hash based on the pmd of addr if configured with MMU, which provides a good
0012  * hit rate for workloads with spatial locality.  Otherwise, use pages.
0013  */
0014 #ifdef CONFIG_MMU
0015 #define VMACACHE_SHIFT  PMD_SHIFT
0016 #else
0017 #define VMACACHE_SHIFT  PAGE_SHIFT
0018 #endif
0019 #define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
0020
0021 /*
0022  * This task may be accessing a foreign mm via (for example)
0023  * get_user_pages()->find_vma().  The vmacache is task-local and this
0024  * task's vmacache pertains to a different mm (ie, its own).  There is
0025  * nothing we can do here.
0026  *
0027  * Also handle the case where a kernel thread has adopted this mm via
0028  * kthread_use_mm(). That kernel thread's vmacache is not applicable to this mm.
0029  */
0030 static inline bool vmacache_valid_mm(struct mm_struct *mm)
0031 {
0032     return current->mm == mm && !(current->flags & PF_KTHREAD);
0033 }
0034
0035 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
0036 {
0037     if (vmacache_valid_mm(newvma->vm_mm))
0038         current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
0039 }
0040
0041 static bool vmacache_valid(struct mm_struct *mm)
0042 {
0043     struct task_struct *curr;
0044
0045     if (!vmacache_valid_mm(mm))
0046         return false;
0047
0048     curr = current;
0049     if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
0050         /*
0051          * First attempt will always be invalid, initialize
0052          * the new cache for this task here.
0053          */
0054         curr->vmacache.seqnum = mm->vmacache_seqnum;
0055         vmacache_flush(curr);
0056         return false;
0057     }
0058     return true;
0059 }
0060
0061 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
0062 {
0063     int idx = VMACACHE_HASH(addr);
0064     int i;
0065
0066     count_vm_vmacache_event(VMACACHE_FIND_CALLS);
0067
0068     if (!vmacache_valid(mm))
0069         return NULL;
0070
0071     for (i = 0; i < VMACACHE_SIZE; i++) {
0072         struct vm_area_struct *vma = current->vmacache.vmas[idx];
0073
0074         if (vma) {
0075 #ifdef CONFIG_DEBUG_VM_VMACACHE
0076             if (WARN_ON_ONCE(vma->vm_mm != mm))
0077                 break;
0078 #endif
0079             if (vma->vm_start <= addr && vma->vm_end > addr) {
0080                 count_vm_vmacache_event(VMACACHE_FIND_HITS);
0081                 return vma;
0082             }
0083         }
0084         if (++idx == VMACACHE_SIZE)
0085             idx = 0;
0086     }
0087
0088     return NULL;
0089 }
0090
0091 #ifndef CONFIG_MMU
0092 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
0093                        unsigned long start,
0094                        unsigned long end)
0095 {
0096     int idx = VMACACHE_HASH(start);
0097     int i;
0098
0099     count_vm_vmacache_event(VMACACHE_FIND_CALLS);
0100
0101     if (!vmacache_valid(mm))
0102         return NULL;
0103
0104     for (i = 0; i < VMACACHE_SIZE; i++) {
0105         struct vm_area_struct *vma = current->vmacache.vmas[idx];
0106
0107         if (vma && vma->vm_start == start && vma->vm_end == end) {
0108             count_vm_vmacache_event(VMACACHE_FIND_HITS);
0109             return vma;
0110         }
0111         if (++idx == VMACACHE_SIZE)
0112             idx = 0;
0113     }
0114
0115     return NULL;
0116 }
0117 #endif