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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * HugeTLB Vmemmap Optimization (HVO)
4 *
5 * Copyright (c) 2020, ByteDance. All rights reserved.
6 *
7 * Author: Muchun Song <songmuchun@bytedance.com>
8 *
9 * See Documentation/mm/vmemmap_dedup.rst
10 */
11#define pr_fmt(fmt) "HugeTLB: " fmt
12
13#include <linux/pgtable.h>
14#include <linux/moduleparam.h>
15#include <linux/bootmem_info.h>
16#include <linux/mmdebug.h>
17#include <linux/pagewalk.h>
18#include <asm/pgalloc.h>
19#include <asm/tlbflush.h>
20#include "hugetlb_vmemmap.h"
21
22/**
23 * struct vmemmap_remap_walk - walk vmemmap page table
24 *
25 * @remap_pte: called for each lowest-level entry (PTE).
26 * @nr_walked: the number of walked pte.
27 * @reuse_page: the page which is reused for the tail vmemmap pages.
28 * @reuse_addr: the virtual address of the @reuse_page page.
29 * @vmemmap_pages: the list head of the vmemmap pages that can be freed
30 * or is mapped from.
31 * @flags: used to modify behavior in vmemmap page table walking
32 * operations.
33 */
34struct vmemmap_remap_walk {
35 void (*remap_pte)(pte_t *pte, unsigned long addr,
36 struct vmemmap_remap_walk *walk);
37 unsigned long nr_walked;
38 struct page *reuse_page;
39 unsigned long reuse_addr;
40 struct list_head *vmemmap_pages;
41
42/* Skip the TLB flush when we split the PMD */
43#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
44/* Skip the TLB flush when we remap the PTE */
45#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1)
46/* synchronize_rcu() to avoid writes from page_ref_add_unless() */
47#define VMEMMAP_SYNCHRONIZE_RCU BIT(2)
48 unsigned long flags;
49};
50
51static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
52 struct vmemmap_remap_walk *walk)
53{
54 pmd_t __pmd;
55 int i;
56 unsigned long addr = start;
57 pte_t *pgtable;
58
59 pgtable = pte_alloc_one_kernel(&init_mm);
60 if (!pgtable)
61 return -ENOMEM;
62
63 pmd_populate_kernel(&init_mm, &__pmd, pgtable);
64
65 for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
66 pte_t entry, *pte;
67 pgprot_t pgprot = PAGE_KERNEL;
68
69 entry = mk_pte(head + i, pgprot);
70 pte = pte_offset_kernel(&__pmd, addr);
71 set_pte_at(&init_mm, addr, pte, entry);
72 }
73
74 spin_lock(&init_mm.page_table_lock);
75 if (likely(pmd_leaf(*pmd))) {
76 /*
77 * Higher order allocations from buddy allocator must be able to
78 * be treated as indepdenent small pages (as they can be freed
79 * individually).
80 */
81 if (!PageReserved(head))
82 split_page(head, get_order(PMD_SIZE));
83
84 /* Make pte visible before pmd. See comment in pmd_install(). */
85 smp_wmb();
86 pmd_populate_kernel(&init_mm, pmd, pgtable);
87 if (!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH))
88 flush_tlb_kernel_range(start, start + PMD_SIZE);
89 } else {
90 pte_free_kernel(&init_mm, pgtable);
91 }
92 spin_unlock(&init_mm.page_table_lock);
93
94 return 0;
95}
96
97static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,
98 unsigned long next, struct mm_walk *walk)
99{
100 int ret = 0;
101 struct page *head;
102 struct vmemmap_remap_walk *vmemmap_walk = walk->private;
103
104 /* Only splitting, not remapping the vmemmap pages. */
105 if (!vmemmap_walk->remap_pte)
106 walk->action = ACTION_CONTINUE;
107
108 spin_lock(&init_mm.page_table_lock);
109 head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL;
110 /*
111 * Due to HugeTLB alignment requirements and the vmemmap
112 * pages being at the start of the hotplugged memory
113 * region in memory_hotplug.memmap_on_memory case. Checking
114 * the vmemmap page associated with the first vmemmap page
115 * if it is self-hosted is sufficient.
116 *
117 * [ hotplugged memory ]
118 * [ section ][...][ section ]
119 * [ vmemmap ][ usable memory ]
120 * ^ | ^ |
121 * +--+ | |
122 * +------------------------+
123 */
124 if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && unlikely(!vmemmap_walk->nr_walked)) {
125 struct page *page = head ? head + pte_index(addr) :
126 pte_page(ptep_get(pte_offset_kernel(pmd, addr)));
127
128 if (PageVmemmapSelfHosted(page))
129 ret = -ENOTSUPP;
130 }
131 spin_unlock(&init_mm.page_table_lock);
132 if (!head || ret)
133 return ret;
134
135 return vmemmap_split_pmd(pmd, head, addr & PMD_MASK, vmemmap_walk);
136}
137
138static int vmemmap_pte_entry(pte_t *pte, unsigned long addr,
139 unsigned long next, struct mm_walk *walk)
140{
141 struct vmemmap_remap_walk *vmemmap_walk = walk->private;
142
143 /*
144 * The reuse_page is found 'first' in page table walking before
145 * starting remapping.
146 */
147 if (!vmemmap_walk->reuse_page)
148 vmemmap_walk->reuse_page = pte_page(ptep_get(pte));
149 else
150 vmemmap_walk->remap_pte(pte, addr, vmemmap_walk);
151 vmemmap_walk->nr_walked++;
152
153 return 0;
154}
155
156static const struct mm_walk_ops vmemmap_remap_ops = {
157 .pmd_entry = vmemmap_pmd_entry,
158 .pte_entry = vmemmap_pte_entry,
159};
160
161static int vmemmap_remap_range(unsigned long start, unsigned long end,
162 struct vmemmap_remap_walk *walk)
163{
164 int ret;
165
166 VM_BUG_ON(!PAGE_ALIGNED(start | end));
167
168 mmap_read_lock(&init_mm);
169 ret = walk_page_range_novma(&init_mm, start, end, &vmemmap_remap_ops,
170 NULL, walk);
171 mmap_read_unlock(&init_mm);
172 if (ret)
173 return ret;
174
175 if (walk->remap_pte && !(walk->flags & VMEMMAP_REMAP_NO_TLB_FLUSH))
176 flush_tlb_kernel_range(start, end);
177
178 return 0;
179}
180
181/*
182 * Free a vmemmap page. A vmemmap page can be allocated from the memblock
183 * allocator or buddy allocator. If the PG_reserved flag is set, it means
184 * that it allocated from the memblock allocator, just free it via the
185 * free_bootmem_page(). Otherwise, use __free_page().
186 */
187static inline void free_vmemmap_page(struct page *page)
188{
189 if (PageReserved(page)) {
190 memmap_boot_pages_add(-1);
191 free_bootmem_page(page);
192 } else {
193 memmap_pages_add(-1);
194 __free_page(page);
195 }
196}
197
198/* Free a list of the vmemmap pages */
199static void free_vmemmap_page_list(struct list_head *list)
200{
201 struct page *page, *next;
202
203 list_for_each_entry_safe(page, next, list, lru)
204 free_vmemmap_page(page);
205}
206
207static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
208 struct vmemmap_remap_walk *walk)
209{
210 /*
211 * Remap the tail pages as read-only to catch illegal write operation
212 * to the tail pages.
213 */
214 pgprot_t pgprot = PAGE_KERNEL_RO;
215 struct page *page = pte_page(ptep_get(pte));
216 pte_t entry;
217
218 /* Remapping the head page requires r/w */
219 if (unlikely(addr == walk->reuse_addr)) {
220 pgprot = PAGE_KERNEL;
221 list_del(&walk->reuse_page->lru);
222
223 /*
224 * Makes sure that preceding stores to the page contents from
225 * vmemmap_remap_free() become visible before the set_pte_at()
226 * write.
227 */
228 smp_wmb();
229 }
230
231 entry = mk_pte(walk->reuse_page, pgprot);
232 list_add(&page->lru, walk->vmemmap_pages);
233 set_pte_at(&init_mm, addr, pte, entry);
234}
235
236/*
237 * How many struct page structs need to be reset. When we reuse the head
238 * struct page, the special metadata (e.g. page->flags or page->mapping)
239 * cannot copy to the tail struct page structs. The invalid value will be
240 * checked in the free_tail_page_prepare(). In order to avoid the message
241 * of "corrupted mapping in tail page". We need to reset at least 3 (one
242 * head struct page struct and two tail struct page structs) struct page
243 * structs.
244 */
245#define NR_RESET_STRUCT_PAGE 3
246
247static inline void reset_struct_pages(struct page *start)
248{
249 struct page *from = start + NR_RESET_STRUCT_PAGE;
250
251 BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
252 memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
253}
254
255static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
256 struct vmemmap_remap_walk *walk)
257{
258 pgprot_t pgprot = PAGE_KERNEL;
259 struct page *page;
260 void *to;
261
262 BUG_ON(pte_page(ptep_get(pte)) != walk->reuse_page);
263
264 page = list_first_entry(walk->vmemmap_pages, struct page, lru);
265 list_del(&page->lru);
266 to = page_to_virt(page);
267 copy_page(to, (void *)walk->reuse_addr);
268 reset_struct_pages(to);
269
270 /*
271 * Makes sure that preceding stores to the page contents become visible
272 * before the set_pte_at() write.
273 */
274 smp_wmb();
275 set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
276}
277
278/**
279 * vmemmap_remap_split - split the vmemmap virtual address range [@start, @end)
280 * backing PMDs of the directmap into PTEs
281 * @start: start address of the vmemmap virtual address range that we want
282 * to remap.
283 * @end: end address of the vmemmap virtual address range that we want to
284 * remap.
285 * @reuse: reuse address.
286 *
287 * Return: %0 on success, negative error code otherwise.
288 */
289static int vmemmap_remap_split(unsigned long start, unsigned long end,
290 unsigned long reuse)
291{
292 struct vmemmap_remap_walk walk = {
293 .remap_pte = NULL,
294 .flags = VMEMMAP_SPLIT_NO_TLB_FLUSH,
295 };
296
297 /* See the comment in the vmemmap_remap_free(). */
298 BUG_ON(start - reuse != PAGE_SIZE);
299
300 return vmemmap_remap_range(reuse, end, &walk);
301}
302
303/**
304 * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
305 * to the page which @reuse is mapped to, then free vmemmap
306 * which the range are mapped to.
307 * @start: start address of the vmemmap virtual address range that we want
308 * to remap.
309 * @end: end address of the vmemmap virtual address range that we want to
310 * remap.
311 * @reuse: reuse address.
312 * @vmemmap_pages: list to deposit vmemmap pages to be freed. It is callers
313 * responsibility to free pages.
314 * @flags: modifications to vmemmap_remap_walk flags
315 *
316 * Return: %0 on success, negative error code otherwise.
317 */
318static int vmemmap_remap_free(unsigned long start, unsigned long end,
319 unsigned long reuse,
320 struct list_head *vmemmap_pages,
321 unsigned long flags)
322{
323 int ret;
324 struct vmemmap_remap_walk walk = {
325 .remap_pte = vmemmap_remap_pte,
326 .reuse_addr = reuse,
327 .vmemmap_pages = vmemmap_pages,
328 .flags = flags,
329 };
330 int nid = page_to_nid((struct page *)reuse);
331 gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
332
333 /*
334 * Allocate a new head vmemmap page to avoid breaking a contiguous
335 * block of struct page memory when freeing it back to page allocator
336 * in free_vmemmap_page_list(). This will allow the likely contiguous
337 * struct page backing memory to be kept contiguous and allowing for
338 * more allocations of hugepages. Fallback to the currently
339 * mapped head page in case should it fail to allocate.
340 */
341 walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
342 if (walk.reuse_page) {
343 copy_page(page_to_virt(walk.reuse_page),
344 (void *)walk.reuse_addr);
345 list_add(&walk.reuse_page->lru, vmemmap_pages);
346 memmap_pages_add(1);
347 }
348
349 /*
350 * In order to make remapping routine most efficient for the huge pages,
351 * the routine of vmemmap page table walking has the following rules
352 * (see more details from the vmemmap_pte_range()):
353 *
354 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
355 * should be continuous.
356 * - The @reuse address is part of the range [@reuse, @end) that we are
357 * walking which is passed to vmemmap_remap_range().
358 * - The @reuse address is the first in the complete range.
359 *
360 * So we need to make sure that @start and @reuse meet the above rules.
361 */
362 BUG_ON(start - reuse != PAGE_SIZE);
363
364 ret = vmemmap_remap_range(reuse, end, &walk);
365 if (ret && walk.nr_walked) {
366 end = reuse + walk.nr_walked * PAGE_SIZE;
367 /*
368 * vmemmap_pages contains pages from the previous
369 * vmemmap_remap_range call which failed. These
370 * are pages which were removed from the vmemmap.
371 * They will be restored in the following call.
372 */
373 walk = (struct vmemmap_remap_walk) {
374 .remap_pte = vmemmap_restore_pte,
375 .reuse_addr = reuse,
376 .vmemmap_pages = vmemmap_pages,
377 .flags = 0,
378 };
379
380 vmemmap_remap_range(reuse, end, &walk);
381 }
382
383 return ret;
384}
385
386static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
387 struct list_head *list)
388{
389 gfp_t gfp_mask = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
390 unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
391 int nid = page_to_nid((struct page *)start);
392 struct page *page, *next;
393 int i;
394
395 for (i = 0; i < nr_pages; i++) {
396 page = alloc_pages_node(nid, gfp_mask, 0);
397 if (!page)
398 goto out;
399 list_add(&page->lru, list);
400 }
401 memmap_pages_add(nr_pages);
402
403 return 0;
404out:
405 list_for_each_entry_safe(page, next, list, lru)
406 __free_page(page);
407 return -ENOMEM;
408}
409
410/**
411 * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
412 * to the page which is from the @vmemmap_pages
413 * respectively.
414 * @start: start address of the vmemmap virtual address range that we want
415 * to remap.
416 * @end: end address of the vmemmap virtual address range that we want to
417 * remap.
418 * @reuse: reuse address.
419 * @flags: modifications to vmemmap_remap_walk flags
420 *
421 * Return: %0 on success, negative error code otherwise.
422 */
423static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
424 unsigned long reuse, unsigned long flags)
425{
426 LIST_HEAD(vmemmap_pages);
427 struct vmemmap_remap_walk walk = {
428 .remap_pte = vmemmap_restore_pte,
429 .reuse_addr = reuse,
430 .vmemmap_pages = &vmemmap_pages,
431 .flags = flags,
432 };
433
434 /* See the comment in the vmemmap_remap_free(). */
435 BUG_ON(start - reuse != PAGE_SIZE);
436
437 if (alloc_vmemmap_page_list(start, end, &vmemmap_pages))
438 return -ENOMEM;
439
440 return vmemmap_remap_range(reuse, end, &walk);
441}
442
443DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
444EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
445
446static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
447core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
448
449static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
450 struct folio *folio, unsigned long flags)
451{
452 int ret;
453 unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
454 unsigned long vmemmap_reuse;
455
456 VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
457 VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
458
459 if (!folio_test_hugetlb_vmemmap_optimized(folio))
460 return 0;
461
462 if (flags & VMEMMAP_SYNCHRONIZE_RCU)
463 synchronize_rcu();
464
465 vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
466 vmemmap_reuse = vmemmap_start;
467 vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
468
469 /*
470 * The pages which the vmemmap virtual address range [@vmemmap_start,
471 * @vmemmap_end) are mapped to are freed to the buddy allocator, and
472 * the range is mapped to the page which @vmemmap_reuse is mapped to.
473 * When a HugeTLB page is freed to the buddy allocator, previously
474 * discarded vmemmap pages must be allocated and remapping.
475 */
476 ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse, flags);
477 if (!ret) {
478 folio_clear_hugetlb_vmemmap_optimized(folio);
479 static_branch_dec(&hugetlb_optimize_vmemmap_key);
480 }
481
482 return ret;
483}
484
485/**
486 * hugetlb_vmemmap_restore_folio - restore previously optimized (by
487 * hugetlb_vmemmap_optimize_folio()) vmemmap pages which
488 * will be reallocated and remapped.
489 * @h: struct hstate.
490 * @folio: the folio whose vmemmap pages will be restored.
491 *
492 * Return: %0 if @folio's vmemmap pages have been reallocated and remapped,
493 * negative error code otherwise.
494 */
495int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
496{
497 return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU);
498}
499
500/**
501 * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
502 * @h: hstate.
503 * @folio_list: list of folios.
504 * @non_hvo_folios: Output list of folios for which vmemmap exists.
505 *
506 * Return: number of folios for which vmemmap was restored, or an error code
507 * if an error was encountered restoring vmemmap for a folio.
508 * Folios that have vmemmap are moved to the non_hvo_folios
509 * list. Processing of entries stops when the first error is
510 * encountered. The folio that experienced the error and all
511 * non-processed folios will remain on folio_list.
512 */
513long hugetlb_vmemmap_restore_folios(const struct hstate *h,
514 struct list_head *folio_list,
515 struct list_head *non_hvo_folios)
516{
517 struct folio *folio, *t_folio;
518 long restored = 0;
519 long ret = 0;
520 unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
521
522 list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
523 if (folio_test_hugetlb_vmemmap_optimized(folio)) {
524 ret = __hugetlb_vmemmap_restore_folio(h, folio, flags);
525 /* only need to synchronize_rcu() once for each batch */
526 flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
527
528 if (ret)
529 break;
530 restored++;
531 }
532
533 /* Add non-optimized folios to output list */
534 list_move(&folio->lru, non_hvo_folios);
535 }
536
537 if (restored)
538 flush_tlb_all();
539 if (!ret)
540 ret = restored;
541 return ret;
542}
543
544/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
545static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *folio)
546{
547 if (folio_test_hugetlb_vmemmap_optimized(folio))
548 return false;
549
550 if (!READ_ONCE(vmemmap_optimize_enabled))
551 return false;
552
553 if (!hugetlb_vmemmap_optimizable(h))
554 return false;
555
556 return true;
557}
558
559static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
560 struct folio *folio,
561 struct list_head *vmemmap_pages,
562 unsigned long flags)
563{
564 int ret = 0;
565 unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
566 unsigned long vmemmap_reuse;
567
568 VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
569 VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
570
571 if (!vmemmap_should_optimize_folio(h, folio))
572 return ret;
573
574 static_branch_inc(&hugetlb_optimize_vmemmap_key);
575
576 if (flags & VMEMMAP_SYNCHRONIZE_RCU)
577 synchronize_rcu();
578 /*
579 * Very Subtle
580 * If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
581 * immediately after remapping. As a result, subsequent accesses
582 * and modifications to struct pages associated with the hugetlb
583 * page could be to the OLD struct pages. Set the vmemmap optimized
584 * flag here so that it is copied to the new head page. This keeps
585 * the old and new struct pages in sync.
586 * If there is an error during optimization, we will immediately FLUSH
587 * the TLB and clear the flag below.
588 */
589 folio_set_hugetlb_vmemmap_optimized(folio);
590
591 vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
592 vmemmap_reuse = vmemmap_start;
593 vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
594
595 /*
596 * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
597 * to the page which @vmemmap_reuse is mapped to. Add pages previously
598 * mapping the range to vmemmap_pages list so that they can be freed by
599 * the caller.
600 */
601 ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse,
602 vmemmap_pages, flags);
603 if (ret) {
604 static_branch_dec(&hugetlb_optimize_vmemmap_key);
605 folio_clear_hugetlb_vmemmap_optimized(folio);
606 }
607
608 return ret;
609}
610
611/**
612 * hugetlb_vmemmap_optimize_folio - optimize @folio's vmemmap pages.
613 * @h: struct hstate.
614 * @folio: the folio whose vmemmap pages will be optimized.
615 *
616 * This function only tries to optimize @folio's vmemmap pages and does not
617 * guarantee that the optimization will succeed after it returns. The caller
618 * can use folio_test_hugetlb_vmemmap_optimized(@folio) to detect if @folio's
619 * vmemmap pages have been optimized.
620 */
621void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
622{
623 LIST_HEAD(vmemmap_pages);
624
625 __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU);
626 free_vmemmap_page_list(&vmemmap_pages);
627}
628
629static int hugetlb_vmemmap_split_folio(const struct hstate *h, struct folio *folio)
630{
631 unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
632 unsigned long vmemmap_reuse;
633
634 if (!vmemmap_should_optimize_folio(h, folio))
635 return 0;
636
637 vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
638 vmemmap_reuse = vmemmap_start;
639 vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
640
641 /*
642 * Split PMDs on the vmemmap virtual address range [@vmemmap_start,
643 * @vmemmap_end]
644 */
645 return vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse);
646}
647
648void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
649{
650 struct folio *folio;
651 LIST_HEAD(vmemmap_pages);
652 unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
653
654 list_for_each_entry(folio, folio_list, lru) {
655 int ret = hugetlb_vmemmap_split_folio(h, folio);
656
657 /*
658 * Spliting the PMD requires allocating a page, thus lets fail
659 * early once we encounter the first OOM. No point in retrying
660 * as it can be dynamically done on remap with the memory
661 * we get back from the vmemmap deduplication.
662 */
663 if (ret == -ENOMEM)
664 break;
665 }
666
667 flush_tlb_all();
668
669 list_for_each_entry(folio, folio_list, lru) {
670 int ret;
671
672 ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
673 /* only need to synchronize_rcu() once for each batch */
674 flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
675
676 /*
677 * Pages to be freed may have been accumulated. If we
678 * encounter an ENOMEM, free what we have and try again.
679 * This can occur in the case that both spliting fails
680 * halfway and head page allocation also failed. In this
681 * case __hugetlb_vmemmap_optimize_folio() would free memory
682 * allowing more vmemmap remaps to occur.
683 */
684 if (ret == -ENOMEM && !list_empty(&vmemmap_pages)) {
685 flush_tlb_all();
686 free_vmemmap_page_list(&vmemmap_pages);
687 INIT_LIST_HEAD(&vmemmap_pages);
688 __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
689 }
690 }
691
692 flush_tlb_all();
693 free_vmemmap_page_list(&vmemmap_pages);
694}
695
696static struct ctl_table hugetlb_vmemmap_sysctls[] = {
697 {
698 .procname = "hugetlb_optimize_vmemmap",
699 .data = &vmemmap_optimize_enabled,
700 .maxlen = sizeof(vmemmap_optimize_enabled),
701 .mode = 0644,
702 .proc_handler = proc_dobool,
703 },
704};
705
706static int __init hugetlb_vmemmap_init(void)
707{
708 const struct hstate *h;
709
710 /* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
711 BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES);
712
713 for_each_hstate(h) {
714 if (hugetlb_vmemmap_optimizable(h)) {
715 register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
716 break;
717 }
718 }
719 return 0;
720}
721late_initcall(hugetlb_vmemmap_init);