1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
|
/*
* linux/mm/madvise.c
*
* Copyright (C) 1999 Linus Torvalds
* Copyright (C) 2002 Christoph Hellwig
*/
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/mempolicy.h>
#include <linux/hugetlb.h>
#include <linux/sched.h>
/*
* Any behaviour which results in changes to the vma->vm_flags needs to
* take mmap_sem for writing. Others, which simply traverse vmas, need
* to only take it for reading.
*/
static int madvise_need_mmap_write(int behavior)
{
switch (behavior) {
case MADV_REMOVE:
case MADV_WILLNEED:
case MADV_DONTNEED:
return 0;
default:
/* be safe, default to 1. list exceptions explicitly */
return 1;
}
}
/*
* We can potentially split a vm area into separate
* areas, each area with its own behavior.
*/
static long madvise_behavior(struct vm_area_struct * vma,
struct vm_area_struct **prev,
unsigned long start, unsigned long end, int behavior)
{
struct mm_struct * mm = vma->vm_mm;
int error = 0;
pgoff_t pgoff;
int new_flags = vma->vm_flags;
switch (behavior) {
case MADV_NORMAL:
new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
break;
case MADV_SEQUENTIAL:
new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
break;
case MADV_RANDOM:
new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
break;
case MADV_DONTFORK:
new_flags |= VM_DONTCOPY;
break;
case MADV_DOFORK:
new_flags &= ~VM_DONTCOPY;
break;
}
if (new_flags == vma->vm_flags) {
*prev = vma;
goto out;
}
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma));
if (*prev) {
vma = *prev;
goto success;
}
*prev = vma;
if (start != vma->vm_start) {
error = split_vma(mm, vma, start, 1);
if (error)
goto out;
}
if (end != vma->vm_end) {
error = split_vma(mm, vma, end, 0);
if (error)
goto out;
}
success:
/*
* vm_flags is protected by the mmap_sem held in write mode.
*/
vma->vm_flags = new_flags;
out:
if (error == -ENOMEM)
error = -EAGAIN;
return error;
}
/*
* Schedule all required I/O operations. Do not wait for completion.
*/
static long madvise_willneed(struct vm_area_struct * vma,
struct vm_area_struct ** prev,
unsigned long start, unsigned long end)
{
struct file *file = vma->vm_file;
if (!file)
return -EBADF;
if (file->f_mapping->a_ops->get_xip_mem) {
/* no bad return value, but ignore advice */
return 0;
}
*prev = vma;
start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
if (end > vma->vm_end)
end = vma->vm_end;
end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
force_page_cache_readahead(file->f_mapping,
file, start, max_sane_readahead(end - start));
return 0;
}
/*
* Application no longer needs these pages. If the pages are dirty,
* it's OK to just throw them away. The app will be more careful about
* data it wants to keep. Be sure to free swap resources too. The
* zap_page_range call sets things up for refill_inactive to actually free
* these pages later if no one else has touched them in the meantime,
* although we could add these pages to a global reuse list for
* refill_inactive to pick up before reclaiming other pages.
*
* NB: This interface discards data rather than pushes it out to swap,
* as some implementations do. This has performance implications for
* applications like large transactional databases which want to discard
* pages in anonymous maps after committing to backing store the data
* that was kept in them. There is no reason to write this data out to
* the swap area if the application is discarding it.
*
* An interface that causes the system to free clean pages and flush
* dirty pages is already available as msync(MS_INVALIDATE).
*/
static long madvise_dontneed(struct vm_area_struct * vma,
struct vm_area_struct ** prev,
unsigned long start, unsigned long end)
{
*prev = vma;
if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
return -EINVAL;
if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
struct zap_details details = {
.nonlinear_vma = vma,
.last_index = ULONG_MAX,
};
zap_page_range(vma, start, end - start, &details);
} else
zap_page_range(vma, start, end - start, NULL);
return 0;
}
/*
* Application wants to free up the pages and associated backing store.
* This is effectively punching a hole into the middle of a file.
*
* NOTE: Currently, only shmfs/tmpfs is supported for this operation.
* Other filesystems return -ENOSYS.
*/
static long madvise_remove(struct vm_area_struct *vma,
struct vm_area_struct **prev,
unsigned long start, unsigned long end)
{
struct address_space *mapping;
loff_t offset, endoff;
int error;
*prev = NULL; /* tell sys_madvise we drop mmap_sem */
if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
return -EINVAL;
if (!vma->vm_file || !vma->vm_file->f_mapping
|| !vma->vm_file->f_mapping->host) {
return -EINVAL;
}
if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
return -EACCES;
mapping = vma->vm_file->f_mapping;
offset = (loff_t)(start - vma->vm_start)
+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
endoff = (loff_t)(end - vma->vm_start - 1)
+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
up_read(¤t->mm->mmap_sem);
error = vmtruncate_range(mapping->host, offset, endoff);
down_read(¤t->mm->mmap_sem);
return error;
}
static long
madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end, int behavior)
{
long error;
switch (behavior) {
case MADV_DOFORK:
if (vma->vm_flags & VM_IO) {
error = -EINVAL;
break;
}
case MADV_DONTFORK:
case MADV_NORMAL:
case MADV_SEQUENTIAL:
case MADV_RANDOM:
error = madvise_behavior(vma, prev, start, end, behavior);
break;
case MADV_REMOVE:
error = madvise_remove(vma, prev, start, end);
break;
case MADV_WILLNEED:
error = madvise_willneed(vma, prev, start, end);
break;
case MADV_DONTNEED:
error = madvise_dontneed(vma, prev, start, end);
break;
default:
error = -EINVAL;
break;
}
return error;
}
/*
* The madvise(2) system call.
*
* Applications can use madvise() to advise the kernel how it should
* handle paging I/O in this VM area. The idea is to help the kernel
* use appropriate read-ahead and caching techniques. The information
* provided is advisory only, and can be safely disregarded by the
* kernel without affecting the correct operation of the application.
*
* behavior values:
* MADV_NORMAL - the default behavior is to read clusters. This
* results in some read-ahead and read-behind.
* MADV_RANDOM - the system should read the minimum amount of data
* on any access, since it is unlikely that the appli-
* cation will need more than what it asks for.
* MADV_SEQUENTIAL - pages in the given range will probably be accessed
* once, so they can be aggressively read ahead, and
* can be freed soon after they are accessed.
* MADV_WILLNEED - the application is notifying the system to read
* some pages ahead.
* MADV_DONTNEED - the application is finished with the given range,
* so the kernel can free resources associated with it.
* MADV_REMOVE - the application wants to free up the given range of
* pages and associated backing store.
*
* return values:
* zero - success
* -EINVAL - start + len < 0, start is not page-aligned,
* "behavior" is not a valid value, or application
* is attempting to release locked or shared pages.
* -ENOMEM - addresses in the specified range are not currently
* mapped, or are outside the AS of the process.
* -EIO - an I/O error occurred while paging in data.
* -EBADF - map exists, but area maps something that isn't a file.
* -EAGAIN - a kernel resource was temporarily unavailable.
*/
asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
{
unsigned long end, tmp;
struct vm_area_struct * vma, *prev;
int unmapped_error = 0;
int error = -EINVAL;
int write;
size_t len;
write = madvise_need_mmap_write(behavior);
if
|