Make __collapse_huge_page_copy return whether
collapsing/copying anonymous pages succeeded,
and make collapse_huge_page handle the return status.
Break existing PTE scan loop into two for-loops.
The first loop copies source pages into target huge page,
and can fail gracefully when running into memory errors in
source pages. Roll back the page table and page states
in the 2nd loop when copy failed:
1) re-establish the PTEs-to-PMD connection.
2) release pages back to their LRU list.
Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
---
include/linux/highmem.h | 19 ++++++
mm/khugepaged.c | 136 ++++++++++++++++++++++++++++++----------
2 files changed, 122 insertions(+), 33 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 39bb9b47fa9c..15d0aa4d349c 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -281,6 +281,25 @@ static inline void copy_user_highpage(struct page *to, struct page *from,
kunmap_local(vfrom);
}
+/*
+ * Machine check exception handled version of copy_user_highpage.
+ * Return true if copying page content failed; otherwise false.
+ */
+static inline bool copy_user_highpage_mc(struct page *to, struct page *from,
+ unsigned long vaddr, struct vm_area_struct *vma)
+{
+ char *vfrom, *vto;
+ unsigned long ret;
+
+ vfrom = kmap_local_page(from);
+ vto = kmap_local_page(to);
+ ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE);
+ kunmap_local(vto);
+ kunmap_local(vfrom);
+
+ return ret > 0;
+}
+
#endif
#ifndef __HAVE_ARCH_COPY_HIGHPAGE
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 131492fd1148..84ed177f56ff 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -739,44 +739,97 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
return 0;
}
-static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
- struct vm_area_struct *vma,
- unsigned long address,
- spinlock_t *ptl,
- struct list_head *compound_pagelist)
+/*
+ * __collapse_huge_page_copy - attempts to copy memory contents from normal
+ * pages to a hugepage. Cleanup the normal pages if copy succeeds;
+ * otherwise restore the original pmd page table.
+ *
+ * @pte: starting of the PTEs to copy from
+ * @page: the new hugepage to copy contents to
+ * @pmd: pointer to the new hugepage's PMD
+ * @rollback: the original normal PTEs' PMD
+ * @address: starting address to copy
+ * @pte_ptl: lock on normal pages' PTEs
+ * @compound_pagelist: list that stores compound pages
+ */
+static bool __collapse_huge_page_copy(pte_t *pte,
+ struct page *page,
+ pmd_t *pmd,
+ pmd_t rollback,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ spinlock_t *pte_ptl,
+ struct list_head *compound_pagelist)
{
struct page *src_page, *tmp;
pte_t *_pte;
- for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
- _pte++, page++, address += PAGE_SIZE) {
- pte_t pteval = *_pte;
+ pte_t pteval;
+ unsigned long _address;
+ spinlock_t *pmd_ptl;
+ bool copy_succeeded = true;
- if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ /*
+ * Copying pages' contents is subject to memory poison at any iteration.
+ */
+ for (_pte = pte, _address = address;
+ _pte < pte + HPAGE_PMD_NR;
+ _pte++, page++, _address += PAGE_SIZE) {
+ pteval = *_pte;
+
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval)))
clear_user_highpage(page, address);
- add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
- if (is_zero_pfn(pte_pfn(pteval))) {
- /*
- * ptl mostly unnecessary.
- */
- spin_lock(ptl);
- ptep_clear(vma->vm_mm, address, _pte);
- spin_unlock(ptl);
+ else {
+ src_page = pte_page(pteval);
+ if (copy_user_highpage_mc(page, src_page, address, vma)) {
+ copy_succeeded = false;
+ break;
+ }
+ }
+ }
+
+ if (!copy_succeeded) {
+ /*
+ * Copying failed, re-establish the regular PMD that
+ * points to regular page table. Since PTEs are still
+ * isolated and locked, acquiring anon_vma_lock is unnecessary.
+ */
+ pmd_ptl = pmd_lock(vma->vm_mm, pmd);
+ pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback));
+ spin_unlock(pmd_ptl);
+ }
+
+ for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
+ _pte++, _address += PAGE_SIZE) {
+ pteval = *_pte;
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ if (copy_succeeded) {
+ add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
+ if (is_zero_pfn(pte_pfn(pteval))) {
+ /*
+ * ptl mostly unnecessary.
+ */
+ spin_lock(pte_ptl);
+ pte_clear(vma->vm_mm, _address, _pte);
+ spin_unlock(pte_ptl);
+ }
}
} else {
src_page = pte_page(pteval);
- copy_user_highpage(page, src_page, address, vma);
if (!PageCompound(src_page))
release_pte_page(src_page);
- /*
- * ptl mostly unnecessary, but preempt has to
- * be disabled to update the per-cpu stats
- * inside page_remove_rmap().
- */
- spin_lock(ptl);
- ptep_clear(vma->vm_mm, address, _pte);
- page_remove_rmap(src_page, false);
- spin_unlock(ptl);
- free_page_and_swap_cache(src_page);
+
+ if (copy_succeeded) {
+ /*
+ * ptl mostly unnecessary, but preempt has to
+ * be disabled to update the per-cpu stats
+ * inside page_remove_rmap().
+ */
+ spin_lock(pte_ptl);
+ pte_clear(vma->vm_mm, _address, _pte);
+ page_remove_rmap(src_page, false);
+ spin_unlock(pte_ptl);
+ free_page_and_swap_cache(src_page);
+ }
}
}
@@ -784,6 +837,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
list_del(&src_page->lru);
release_pte_page(src_page);
}
+
+ return copy_succeeded;
}
static void khugepaged_alloc_sleep(void)
@@ -1066,6 +1121,7 @@ static void collapse_huge_page(struct mm_struct *mm,
struct vm_area_struct *vma;
struct mmu_notifier_range range;
gfp_t gfp;
+ bool copy_succeeded = false;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -1177,9 +1233,13 @@ static void collapse_huge_page(struct mm_struct *mm,
*/
anon_vma_unlock_write(vma->anon_vma);
- __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
- &compound_pagelist);
+ copy_succeeded = __collapse_huge_page_copy(pte, new_page, pmd, _pmd,
+ vma, address, pte_ptl, &compound_pagelist);
pte_unmap(pte);
+ if (!copy_succeeded) {
+ result = SCAN_FAIL;
+ goto out_up_write;
+ }
/*
* spin_lock() below is not the equivalent of smp_wmb(), but
* the smp_wmb() inside __SetPageUptodate() can be reused to
@@ -1364,9 +1424,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
pte_unmap_unlock(pte, ptl);
if (ret) {
node = khugepaged_find_target_node();
- /* collapse_huge_page will return with the mmap_lock released */
- collapse_huge_page(mm, address, hpage, node,
- referenced, unmapped);
+ /*
+ * collapse_huge_page will return with the mmap_r+w_lock released.
+ * It is uncertain if *hpage is NULL or not when collapse_huge_page
+ * returns, so keep ret=1 to jump to breakouterloop_mmap_lock
+ * in khugepaged_scan_mm_slot, then *hpage will be freed
+ * if collapse failed.
+ */
+ collapse_huge_page(mm, address, hpage, node, referenced, unmapped);
}
out:
trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
@@ -2168,6 +2233,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
khugepaged_scan_file(mm, file, pgoff, hpage);
fput(file);
} else {
+ /*
+ * mmap_read_lock is
+ * 1) released if both scan and collapse succeeded;
+ * 2) still held if either scan or collapse failed.
+ */
ret = khugepaged_scan_pmd(mm, vma,
khugepaged_scan.address,
hpage);
--
2.35.1.894.gb6a874cedc-goog
