forked from torvalds/linux
-
Notifications
You must be signed in to change notification settings - Fork 0
/
hugetlb_vmemmap.c
582 lines (499 loc) · 15.9 KB
/
hugetlb_vmemmap.c
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
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
// SPDX-License-Identifier: GPL-2.0
/*
* HugeTLB Vmemmap Optimization (HVO)
*
* Copyright (c) 2020, ByteDance. All rights reserved.
*
* Author: Muchun Song <[email protected]>
*
* See Documentation/mm/vmemmap_dedup.rst
*/
#define pr_fmt(fmt) "HugeTLB: " fmt
#include <linux/pgtable.h>
#include <linux/bootmem_info.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "hugetlb_vmemmap.h"
/**
* struct vmemmap_remap_walk - walk vmemmap page table
*
* @remap_pte: called for each lowest-level entry (PTE).
* @nr_walked: the number of walked pte.
* @reuse_page: the page which is reused for the tail vmemmap pages.
* @reuse_addr: the virtual address of the @reuse_page page.
* @vmemmap_pages: the list head of the vmemmap pages that can be freed
* or is mapped from.
*/
struct vmemmap_remap_walk {
void (*remap_pte)(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk);
unsigned long nr_walked;
struct page *reuse_page;
unsigned long reuse_addr;
struct list_head *vmemmap_pages;
};
static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
{
pmd_t __pmd;
int i;
unsigned long addr = start;
struct page *page = pmd_page(*pmd);
pte_t *pgtable = pte_alloc_one_kernel(&init_mm);
if (!pgtable)
return -ENOMEM;
pmd_populate_kernel(&init_mm, &__pmd, pgtable);
for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
pte_t entry, *pte;
pgprot_t pgprot = PAGE_KERNEL;
entry = mk_pte(page + i, pgprot);
pte = pte_offset_kernel(&__pmd, addr);
set_pte_at(&init_mm, addr, pte, entry);
}
spin_lock(&init_mm.page_table_lock);
if (likely(pmd_leaf(*pmd))) {
/*
* Higher order allocations from buddy allocator must be able to
* be treated as indepdenent small pages (as they can be freed
* individually).
*/
if (!PageReserved(page))
split_page(page, get_order(PMD_SIZE));
/* Make pte visible before pmd. See comment in pmd_install(). */
smp_wmb();
pmd_populate_kernel(&init_mm, pmd, pgtable);
flush_tlb_kernel_range(start, start + PMD_SIZE);
} else {
pte_free_kernel(&init_mm, pgtable);
}
spin_unlock(&init_mm.page_table_lock);
return 0;
}
static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
{
int leaf;
spin_lock(&init_mm.page_table_lock);
leaf = pmd_leaf(*pmd);
spin_unlock(&init_mm.page_table_lock);
if (!leaf)
return 0;
return __split_vmemmap_huge_pmd(pmd, start);
}
static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end,
struct vmemmap_remap_walk *walk)
{
pte_t *pte = pte_offset_kernel(pmd, addr);
/*
* The reuse_page is found 'first' in table walk before we start
* remapping (which is calling @walk->remap_pte).
*/
if (!walk->reuse_page) {
walk->reuse_page = pte_page(*pte);
/*
* Because the reuse address is part of the range that we are
* walking, skip the reuse address range.
*/
addr += PAGE_SIZE;
pte++;
walk->nr_walked++;
}
for (; addr != end; addr += PAGE_SIZE, pte++) {
walk->remap_pte(pte, addr, walk);
walk->nr_walked++;
}
}
static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
unsigned long end,
struct vmemmap_remap_walk *walk)
{
pmd_t *pmd;
unsigned long next;
pmd = pmd_offset(pud, addr);
do {
int ret;
ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
if (ret)
return ret;
next = pmd_addr_end(addr, end);
vmemmap_pte_range(pmd, addr, next, walk);
} while (pmd++, addr = next, addr != end);
return 0;
}
static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
unsigned long end,
struct vmemmap_remap_walk *walk)
{
pud_t *pud;
unsigned long next;
pud = pud_offset(p4d, addr);
do {
int ret;
next = pud_addr_end(addr, end);
ret = vmemmap_pmd_range(pud, addr, next, walk);
if (ret)
return ret;
} while (pud++, addr = next, addr != end);
return 0;
}
static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
unsigned long end,
struct vmemmap_remap_walk *walk)
{
p4d_t *p4d;
unsigned long next;
p4d = p4d_offset(pgd, addr);
do {
int ret;
next = p4d_addr_end(addr, end);
ret = vmemmap_pud_range(p4d, addr, next, walk);
if (ret)
return ret;
} while (p4d++, addr = next, addr != end);
return 0;
}
static int vmemmap_remap_range(unsigned long start, unsigned long end,
struct vmemmap_remap_walk *walk)
{
unsigned long addr = start;
unsigned long next;
pgd_t *pgd;
VM_BUG_ON(!PAGE_ALIGNED(start));
VM_BUG_ON(!PAGE_ALIGNED(end));
pgd = pgd_offset_k(addr);
do {
int ret;
next = pgd_addr_end(addr, end);
ret = vmemmap_p4d_range(pgd, addr, next, walk);
if (ret)
return ret;
} while (pgd++, addr = next, addr != end);
/*
* We only change the mapping of the vmemmap virtual address range
* [@start + PAGE_SIZE, end), so we only need to flush the TLB which
* belongs to the range.
*/
flush_tlb_kernel_range(start + PAGE_SIZE, end);
return 0;
}
/*
* Free a vmemmap page. A vmemmap page can be allocated from the memblock
* allocator or buddy allocator. If the PG_reserved flag is set, it means
* that it allocated from the memblock allocator, just free it via the
* free_bootmem_page(). Otherwise, use __free_page().
*/
static inline void free_vmemmap_page(struct page *page)
{
if (PageReserved(page))
free_bootmem_page(page);
else
__free_page(page);
}
/* Free a list of the vmemmap pages */
static void free_vmemmap_page_list(struct list_head *list)
{
struct page *page, *next;
list_for_each_entry_safe(page, next, list, lru) {
list_del(&page->lru);
free_vmemmap_page(page);
}
}
static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk)
{
/*
* Remap the tail pages as read-only to catch illegal write operation
* to the tail pages.
*/
pgprot_t pgprot = PAGE_KERNEL_RO;
pte_t entry = mk_pte(walk->reuse_page, pgprot);
struct page *page = pte_page(*pte);
list_add_tail(&page->lru, walk->vmemmap_pages);
set_pte_at(&init_mm, addr, pte, entry);
}
/*
* How many struct page structs need to be reset. When we reuse the head
* struct page, the special metadata (e.g. page->flags or page->mapping)
* cannot copy to the tail struct page structs. The invalid value will be
* checked in the free_tail_pages_check(). In order to avoid the message
* of "corrupted mapping in tail page". We need to reset at least 3 (one
* head struct page struct and two tail struct page structs) struct page
* structs.
*/
#define NR_RESET_STRUCT_PAGE 3
static inline void reset_struct_pages(struct page *start)
{
struct page *from = start + NR_RESET_STRUCT_PAGE;
BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
}
static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk)
{
pgprot_t pgprot = PAGE_KERNEL;
struct page *page;
void *to;
BUG_ON(pte_page(*pte) != walk->reuse_page);
page = list_first_entry(walk->vmemmap_pages, struct page, lru);
list_del(&page->lru);
to = page_to_virt(page);
copy_page(to, (void *)walk->reuse_addr);
reset_struct_pages(to);
/*
* Makes sure that preceding stores to the page contents become visible
* before the set_pte_at() write.
*/
smp_wmb();
set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
}
/**
* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
* to the page which @reuse is mapped to, then free vmemmap
* which the range are mapped to.
* @start: start address of the vmemmap virtual address range that we want
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_free(unsigned long start, unsigned long end,
unsigned long reuse)
{
int ret;
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_remap_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
};
/*
* In order to make remapping routine most efficient for the huge pages,
* the routine of vmemmap page table walking has the following rules
* (see more details from the vmemmap_pte_range()):
*
* - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
* should be continuous.
* - The @reuse address is part of the range [@reuse, @end) that we are
* walking which is passed to vmemmap_remap_range().
* - The @reuse address is the first in the complete range.
*
* So we need to make sure that @start and @reuse meet the above rules.
*/
BUG_ON(start - reuse != PAGE_SIZE);
mmap_read_lock(&init_mm);
ret = vmemmap_remap_range(reuse, end, &walk);
if (ret && walk.nr_walked) {
end = reuse + walk.nr_walked * PAGE_SIZE;
/*
* vmemmap_pages contains pages from the previous
* vmemmap_remap_range call which failed. These
* are pages which were removed from the vmemmap.
* They will be restored in the following call.
*/
walk = (struct vmemmap_remap_walk) {
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
};
vmemmap_remap_range(reuse, end, &walk);
}
mmap_read_unlock(&init_mm);
free_vmemmap_page_list(&vmemmap_pages);
return ret;
}
static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
gfp_t gfp_mask, struct list_head *list)
{
unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
int nid = page_to_nid((struct page *)start);
struct page *page, *next;
while (nr_pages--) {
page = alloc_pages_node(nid, gfp_mask, 0);
if (!page)
goto out;
list_add_tail(&page->lru, list);
}
return 0;
out:
list_for_each_entry_safe(page, next, list, lru)
__free_pages(page, 0);
return -ENOMEM;
}
/**
* vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
* to the page which is from the @vmemmap_pages
* respectively.
* @start: start address of the vmemmap virtual address range that we want
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
* @gfp_mask: GFP flag for allocating vmemmap pages.
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
unsigned long reuse, gfp_t gfp_mask)
{
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
};
/* See the comment in the vmemmap_remap_free(). */
BUG_ON(start - reuse != PAGE_SIZE);
if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
return -ENOMEM;
mmap_read_lock(&init_mm);
vmemmap_remap_range(reuse, end, &walk);
mmap_read_unlock(&init_mm);
return 0;
}
DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
/**
* hugetlb_vmemmap_restore - restore previously optimized (by
* hugetlb_vmemmap_optimize()) vmemmap pages which
* will be reallocated and remapped.
* @h: struct hstate.
* @head: the head page whose vmemmap pages will be restored.
*
* Return: %0 if @head's vmemmap pages have been reallocated and remapped,
* negative error code otherwise.
*/
int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
{
int ret;
unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
unsigned long vmemmap_reuse;
if (!HPageVmemmapOptimized(head))
return 0;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* The pages which the vmemmap virtual address range [@vmemmap_start,
* @vmemmap_end) are mapped to are freed to the buddy allocator, and
* the range is mapped to the page which @vmemmap_reuse is mapped to.
* When a HugeTLB page is freed to the buddy allocator, previously
* discarded vmemmap pages must be allocated and remapping.
*/
ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse,
GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
if (!ret) {
ClearHPageVmemmapOptimized(head);
static_branch_dec(&hugetlb_optimize_vmemmap_key);
}
return ret;
}
/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
{
if (!READ_ONCE(vmemmap_optimize_enabled))
return false;
if (!hugetlb_vmemmap_optimizable(h))
return false;
if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
pmd_t *pmdp, pmd;
struct page *vmemmap_page;
unsigned long vaddr = (unsigned long)head;
/*
* Only the vmemmap page's vmemmap page can be self-hosted.
* Walking the page tables to find the backing page of the
* vmemmap page.
*/
pmdp = pmd_off_k(vaddr);
/*
* The READ_ONCE() is used to stabilize *pmdp in a register or
* on the stack so that it will stop changing under the code.
* The only concurrent operation where it can be changed is
* split_vmemmap_huge_pmd() (*pmdp will be stable after this
* operation).
*/
pmd = READ_ONCE(*pmdp);
if (pmd_leaf(pmd))
vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
else
vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
/*
* Due to HugeTLB alignment requirements and the vmemmap pages
* being at the start of the hotplugged memory region in
* memory_hotplug.memmap_on_memory case. Checking any vmemmap
* page's vmemmap page if it is marked as VmemmapSelfHosted is
* sufficient.
*
* [ hotplugged memory ]
* [ section ][...][ section ]
* [ vmemmap ][ usable memory ]
* ^ | | |
* +---+ | |
* ^ | |
* +-------+ |
* ^ |
* +-------------------------------------------+
*/
if (PageVmemmapSelfHosted(vmemmap_page))
return false;
}
return true;
}
/**
* hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
* @h: struct hstate.
* @head: the head page whose vmemmap pages will be optimized.
*
* This function only tries to optimize @head's vmemmap pages and does not
* guarantee that the optimization will succeed after it returns. The caller
* can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
* have been optimized.
*/
void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
{
unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
unsigned long vmemmap_reuse;
if (!vmemmap_should_optimize(h, head))
return;
static_branch_inc(&hugetlb_optimize_vmemmap_key);
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
* to the page which @vmemmap_reuse is mapped to, then free the pages
* which the range [@vmemmap_start, @vmemmap_end] is mapped to.
*/
if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
static_branch_dec(&hugetlb_optimize_vmemmap_key);
else
SetHPageVmemmapOptimized(head);
}
static struct ctl_table hugetlb_vmemmap_sysctls[] = {
{
.procname = "hugetlb_optimize_vmemmap",
.data = &vmemmap_optimize_enabled,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dobool,
},
{ }
};
static int __init hugetlb_vmemmap_init(void)
{
/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
BUILD_BUG_ON(__NR_USED_SUBPAGE * sizeof(struct page) > HUGETLB_VMEMMAP_RESERVE_SIZE);
if (IS_ENABLED(CONFIG_PROC_SYSCTL)) {
const struct hstate *h;
for_each_hstate(h) {
if (hugetlb_vmemmap_optimizable(h)) {
register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
break;
}
}
}
return 0;
}
late_initcall(hugetlb_vmemmap_init);