在 2022/3/24 7:29, Jiaqi Yan 写道:
Make collapse_file roll back when copying pages failed.
More concretely:
* extract copy operations into a separate loop
* postpone the updates for nr_none until both scan and copy succeeded
* postpone joining small xarray entries until both scan and copy
succeeded
* as for update operations to NR_XXX_THPS
* for SHMEM file, postpone until both scan and copy succeeded
* for other file, roll back if scan succeeded but copy failed
Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
---
include/linux/highmem.h | 18 ++++++++++
mm/khugepaged.c | 75 +++++++++++++++++++++++++++--------------
2 files changed, 67 insertions(+), 26 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 15d0aa4d349c..fc5aa221bdb5 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -315,6 +315,24 @@ static inline void copy_highpage(struct page *to, struct page *from)
kunmap_local(vfrom);
}
+/*
+ * Machine check exception handled version of copy_highpage.
+ * Return true if copying page content failed; otherwise false.
+ */
+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;
+}
+
#endif
static inline void memcpy_page(struct page *dst_page, size_t dst_off,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 84ed177f56ff..ed2b1cd4bbc6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1708,12 +1708,13 @@ static void collapse_file(struct mm_struct *mm,
{
struct address_space *mapping = file->f_mapping;
gfp_t gfp;
- struct page *new_page;
+ struct page *new_page, *page, *tmp;
pgoff_t index, end = start + HPAGE_PMD_NR;
LIST_HEAD(pagelist);
XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
int nr_none = 0, result = SCAN_SUCCEED;
bool is_shmem = shmem_file(file);
+ bool copy_failed = false;
int nr;
VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
@@ -1936,9 +1937,7 @@ static void collapse_file(struct mm_struct *mm,
}
nr = thp_nr_pages(new_page);
- if (is_shmem)
- __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
- else {
+ if (!is_shmem) {
__mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
filemap_nr_thps_inc(mapping);
/*
@@ -1956,34 +1955,39 @@ static void collapse_file(struct mm_struct *mm,
}
}
- if (nr_none) {
- __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
- if (is_shmem)
- __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
- }
-
- /* Join all the small entries into a single multi-index entry */
- xas_set_order(&xas, start, HPAGE_PMD_ORDER);
- xas_store(&xas, new_page);
xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
if (result == SCAN_SUCCEED) {
- struct page *page, *tmp;
-
/*
* Replacing old pages with new one has succeeded, now we
- * need to copy the content and free the old pages.
+ * attempt to copy the contents.
*/
index = start;
- list_for_each_entry_safe(page, tmp, &pagelist, lru) {
+ list_for_each_entry(page, &pagelist, lru) {
while (index < page->index) {
clear_highpage(new_page + (index % HPAGE_PMD_NR));
index++;
}
- copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
- page);
+ if (copy_highpage_mc(new_page + (page->index % HPAGE_PMD_NR), page)) {
+ copy_failed = true;
The 1st patch here used "copy_succeed = false", It is best that the
logic of the two positions can be unified.
+ break;
+ }
+ index++;
+ }
+ while (!copy_failed && index < end) {
+ clear_highpage(new_page + (page->index % HPAGE_PMD_NR));
+ index++;
+ }
+ }
+
+ if (result == SCAN_SUCCEED && !copy_failed) {
+ /*
+ * Copying old pages to huge one has succeeded, now we
+ * need to free the old pages.
+ */
+ list_for_each_entry_safe(page, tmp, &pagelist, lru) {
list_del(&page->lru);
page->mapping = NULL;
page_ref_unfreeze(page, 1);
@@ -1991,12 +1995,20 @@ static void collapse_file(struct mm_struct *mm,
ClearPageUnevictable(page);
unlock_page(page);
put_page(page);
- index++;
}
- while (index < end) {
- clear_highpage(new_page + (index % HPAGE_PMD_NR));
- index++;
+
+ xas_lock_irq(&xas);
+ if (is_shmem)
+ __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
+ if (nr_none) {
+ __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
+ if (is_shmem)
+ __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
}
+ /* Join all the small entries into a single multi-index entry. */
+ xas_set_order(&xas, start, HPAGE_PMD_ORDER);
+ xas_store(&xas, new_page);
+ xas_unlock_irq(&xas);
SetPageUptodate(new_page);
page_ref_add(new_page, HPAGE_PMD_NR - 1);
@@ -2012,9 +2024,11 @@ static void collapse_file(struct mm_struct *mm,
khugepaged_pages_collapsed++;
} else {
- struct page *page;
-
- /* Something went wrong: roll back page cache changes */
+ /*
+ * Something went wrong:
+ * either result != SCAN_SUCCEED or copy_failed,
+ * roll back page cache changes
+ */
xas_lock_irq(&xas);
mapping->nrpages -= nr_none;
@@ -2047,6 +2061,15 @@ static void collapse_file(struct mm_struct *mm,
xas_lock_irq(&xas);
}
VM_BUG_ON(nr_none);
+ /*
+ * Undo the updates of thp_nr_pages(new_page) for non-SHMEM file,
+ * which is not updated yet for SHMEM file.
+ * These undos are not needed if result is not SCAN_SUCCEED.
+ */
+ if (!is_shmem && result == SCAN_SUCCEED) {
+ __mod_lruvec_page_state(new_page, NR_FILE_THPS, -nr);
+ filemap_nr_thps_dec(mapping);
+ }
xas_unlock_irq(&xas);
new_page->mapping = NULL;
