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. If copying all pages succeeds, the second loop
releases and clears up these normal pages.
Otherwise, the second loop does the following to
roll back the page table and page states:
1) re-establish the original PTEs-to-PMD connection.
2) release source pages back to their LRU list.
Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
---
include/linux/highmem.h | 19 +++++
include/trace/events/huge_memory.h | 3 +-
mm/khugepaged.c | 130 ++++++++++++++++++++++-------
3 files changed, 121 insertions(+), 31 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 39bb9b47fa9cd..0ccb1e92c4b06 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from)
#endif
+/*
+ * Machine check exception handled version of copy_highpage.
+ * Return true if copying page content failed; otherwise false.
+ * Note handling #MC requires arch opt-in.
+ */
+static inline bool copy_highpage_mc(struct page *to, struct page *from)
+{
+ 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;
+}
+
static inline void memcpy_page(struct page *dst_page, size_t dst_off,
struct page *src_page, size_t src_off,
size_t len)
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 4fdb14a81108b..f08687046ce41 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -34,7 +34,8 @@
EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \
EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \
EM( SCAN_TRUNCATED, "truncated") \
- EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
+ EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
+ EMe(SCAN_COPY_MC, "copy_poisoned_page") \
#undef EM
#undef EMe
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 131492fd1148b..0dd28ecc915d1 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -52,6 +52,7 @@ enum scan_result {
SCAN_CGROUP_CHARGE_FAIL,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
+ SCAN_COPY_MC,
};
#define CREATE_TRACE_POINTS
@@ -739,44 +740,99 @@ 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 copying succeeds;
+ * otherwise restore the original page table and release isolated normal pages.
+ * Returns true if copying succeeds, otherwise returns false.
+ *
+ * @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 pages' 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_highpage_mc(page, src_page)) {
+ copy_succeeded = false;
+ break;
+ }
+ }
+ }
+
+ if (!copy_succeeded) {
+ /*
+ * Copying failed, re-establish the regular PMD that points to
+ * the regular page table. Restoring PMD needs to be done prior
+ * to releasing pages. Since pages are still isolated and locked
+ * here, acquiring anon_vma_lock_write 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 +840,8 @@ 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 +1124,7 @@ static void collapse_huge_page(struct mm_struct *mm,
struct vm_area_struct *vma;
struct mmu_notifier_range range;
gfp_t gfp;
+ bool copied = false;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -1177,9 +1236,13 @@ 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);
+ copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd,
+ vma, address, pte_ptl, &compound_pagelist);
pte_unmap(pte);
+ if (!copied) {
+ result = SCAN_COPY_MC;
+ goto out_up_write;
+ }
/*
* spin_lock() below is not the equivalent of smp_wmb(), but
* the smp_wmb() inside __SetPageUptodate() can be reused to
@@ -2168,6 +2231,13 @@ 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) still held if scan failed;
+ * 2) released if scan succeeded.
+ * It is not affected by collapsing or copying
+ * operations.
+ */
ret = khugepaged_scan_pmd(mm, vma,
khugepaged_scan.address,
hpage);
--
2.36.1.124.g0e6072fb45-goog
