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mm/huge_memory: do not change split_huge_page*() target order silently

Page cache folios from a file system that support large block size (LBS) can have minimal folio order greater than 0, thus a high order folio might not be able to be split down to order-0. Commit e220917fa507 ("mm: split a folio in minimum folio order chunks") bumps the target order of split_huge_page*() to the minimum allowed order when splitting a LBS folio. This causes confusion for some split_huge_page*() callers like memory failure handling code, since they expect after-split folios all have order-0 when split succeeds but in reality get min_order_for_split() order folios and give warnings. Fix it by failing a split if the folio cannot be split to the target order. Rename try_folio_split() to try_folio_split_to_order() to reflect the added new_order parameter. Remove its unused list parameter. [The test poisons LBS folios, which cannot be split to order-0 folios, and also tries to poison all memory. The non split LBS folios take more memory than the test anticipated, leading to OOM. The patch fixed the kernel warning and the test needs some change to avoid OOM.]

Zi Yan committed 1 year ago

Commit 77008e11 parent e9a6fb03 files · +28 −42Browse files

Unified · Split

3 files
  1. include/linux/huge_mm.h +23 −32
  2. mm/huge_memory.c +1 −8
  3. mm/truncate.c +4 −2
include/linux/huge_mm.h+23−32
@@ -376,45 +376,30 @@ bool non_uniform_split_supported(struct folio *folio, unsigned int new_order, · 375 unmodified lines
376int folio_split(struct folio *folio, unsigned int new_order, struct page *page,376int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
377 struct list_head *list);377 struct list_head *list);
378/*378/*
379 * try_folio_split - try to split a @folio at @page using non uniform split.379 * try_folio_split_to_order - try to split a @folio at @page to @new_order using
380 * non uniform split.
380 * @folio: folio to be split381 * @folio: folio to be split
381 * @page: split to order-0 at the given page382 * @page: split to @new_order at the given page
382 * @list: store the after-split folios383 * @new_order: the target split order
383 *384 *
384 * Try to split a @folio at @page using non uniform split to order-0, if385 * Try to split a @folio at @page using non uniform split to @new_order, if
385 * non uniform split is not supported, fall back to uniform split.386 * non uniform split is not supported, fall back to uniform split. After-split
387 * folios are put back to LRU list. Use min_order_for_split() to get the lower
388 * bound of @new_order.
386 *389 *
387 * Return: 0: split is successful, otherwise split failed.390 * Return: 0: split is successful, otherwise split failed.
388 */391 */
389static inline int try_folio_split(struct folio *folio, struct page *page,392static inline int try_folio_split_to_order(struct folio *folio,
390 struct list_head *list)393 struct page *page, unsigned int new_order)
391{394{
392 int ret = min_order_for_split(folio);395 if (!non_uniform_split_supported(folio, new_order, /* warns= */ false))
393 396 return split_huge_page_to_list_to_order(&folio->page, NULL,
394 if (ret < 0)397 new_order);
395 return ret;398 return folio_split(folio, new_order, page, NULL);
396
397 if (!non_uniform_split_supported(folio, 0, false))
398 return split_huge_page_to_list_to_order(&folio->page, list,
399 ret);
400 return folio_split(folio, ret, page, list);
401}399}
402static inline int split_huge_page(struct page *page)400static inline int split_huge_page(struct page *page)
403{401{
404 struct folio *folio = page_folio(page);402 return split_huge_page_to_list_to_order(page, NULL, 0);
405 int ret = min_order_for_split(folio);
406
407 if (ret < 0)
408 return ret;
409
410 /*
411 * split_huge_page() locks the page before splitting and
412 * expects the same page that has been split to be locked when
413 * returned. split_folio(page_folio(page)) cannot be used here
414 * because it converts the page to folio and passes the head
415 * page to be split.
416 */
417 return split_huge_page_to_list_to_order(page, NULL, ret);
418}403}
419void deferred_split_folio(struct folio *folio, bool partially_mapped);404void deferred_split_folio(struct folio *folio, bool partially_mapped);
420 405
@@ -597,14 +582,20 @@ static inline int split_huge_page(struct page *page) · 176 unmodified lines
597 return -EINVAL;582 return -EINVAL;
598}583}
599 584
585static inline int min_order_for_split(struct folio *folio)
586{
587 VM_WARN_ON_ONCE_FOLIO(1, folio);
588 return -EINVAL;
589}
590
600static inline int split_folio_to_list(struct folio *folio, struct list_head *list)591static inline int split_folio_to_list(struct folio *folio, struct list_head *list)
601{592{
602 VM_WARN_ON_ONCE_FOLIO(1, folio);593 VM_WARN_ON_ONCE_FOLIO(1, folio);
603 return -EINVAL;594 return -EINVAL;
604}595}
605 596
606static inline int try_folio_split(struct folio *folio, struct page *page,597static inline int try_folio_split_to_order(struct folio *folio,
607 struct list_head *list)598 struct page *page, unsigned int new_order)
608{599{
609 VM_WARN_ON_ONCE_FOLIO(1, folio);600 VM_WARN_ON_ONCE_FOLIO(1, folio);
610 return -EINVAL;601 return -EINVAL;
mm/huge_memory.c+1−8
@@ -3653,8 +3653,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order, · 3652 unmodified lines
3653 3653
3654 min_order = mapping_min_folio_order(folio->mapping);3654 min_order = mapping_min_folio_order(folio->mapping);
3655 if (new_order < min_order) {3655 if (new_order < min_order) {
3656 VM_WARN_ONCE(1, "Cannot split mapped folio below min-order: %u",
3657 min_order);
3658 ret = -EINVAL;3656 ret = -EINVAL;
3659 goto out;3657 goto out;
3660 }3658 }
@@ -3986,12 +3984,7 @@ int min_order_for_split(struct folio *folio) · 325 unmodified lines
3986 3984
3987int split_folio_to_list(struct folio *folio, struct list_head *list)3985int split_folio_to_list(struct folio *folio, struct list_head *list)
3988{3986{
3989 int ret = min_order_for_split(folio);3987 return split_huge_page_to_list_to_order(&folio->page, list, 0);
3990
3991 if (ret < 0)
3992 return ret;
3993
3994 return split_huge_page_to_list_to_order(&folio->page, list, ret);
3995}3988}
3996 3989
3997/*3990/*
mm/truncate.c+4−2
@@ -194,6 +194,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) · 193 unmodified lines
194 size_t size = folio_size(folio);194 size_t size = folio_size(folio);
195 unsigned int offset, length;195 unsigned int offset, length;
196 struct page *split_at, *split_at2;196 struct page *split_at, *split_at2;
197 unsigned int min_order;
197 198
198 if (pos < start)199 if (pos < start)
199 offset = start - pos;200 offset = start - pos;
@@ -223,8 +224,9 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) · 23 unmodified lines
223 if (!folio_test_large(folio))224 if (!folio_test_large(folio))
224 return true;225 return true;
225 226
227 min_order = mapping_min_folio_order(folio->mapping);
226 split_at = folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE);228 split_at = folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE);
227 if (!try_folio_split(folio, split_at, NULL)) {229 if (!try_folio_split_to_order(folio, split_at, min_order)) {
228 /*230 /*
229 * try to split at offset + length to make sure folios within231 * try to split at offset + length to make sure folios within
230 * the range can be dropped, especially to avoid memory waste232 * the range can be dropped, especially to avoid memory waste
@@ -254,7 +256,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) · 23 unmodified lines
254 */256 */
255 if (folio_test_large(folio2) &&257 if (folio_test_large(folio2) &&
256 folio2->mapping == folio->mapping)258 folio2->mapping == folio->mapping)
257 try_folio_split(folio2, split_at2, NULL);259 try_folio_split_to_order(folio2, split_at2, min_order);
258 260
259 folio_unlock(folio2);261 folio_unlock(folio2);
260out:262out: