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Subject[RFC PATCH v2 22/30] mm: thp: split PUD THPs at page reclaim.
Date
From: Zi Yan <ziy@nvidia.com>

We cannot swap PUD THPs, so split them before swap them out. PUD THPs
will be split into PMD THPs, so that if THP_SWAP is enabled, PMD THPs
can be swapped out as a whole.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
mm/swap_slots.c | 2 ++
mm/vmscan.c | 33 +++++++++++++++++++++++++++------
2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 3e6453573a89..65b8742a0446 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -312,6 +312,8 @@ swp_entry_t get_swap_page(struct page *page)
entry.val = 0;

if (PageTransHuge(page)) {
+ if (compound_order(page) == HPAGE_PUD_ORDER)
+ return entry;
if (IS_ENABLED(CONFIG_THP_SWAP))
get_swap_pages(1, &entry, HPAGE_PMD_NR);
goto out;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index eae57d092931..12e169af663c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1244,7 +1244,21 @@ static unsigned int shrink_page_list(struct list_head *page_list,
if (!PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
- if (PageTransHuge(page)) {
+ if (!PageTransHuge(page))
+ goto try_to_swap;
+ if (compound_order(page) == HPAGE_PUD_ORDER) {
+ /* cannot split THP, skip it */
+ if (!can_split_huge_pud_page(page, NULL))
+ goto activate_locked;
+ /* Split PUD THPs before swapping */
+ if (split_huge_pud_page_to_list(page, page_list))
+ goto activate_locked;
+ else {
+ sc->nr_scanned -= (nr_pages - HPAGE_PMD_NR);
+ nr_pages = HPAGE_PMD_NR;
+ }
+ }
+ if (compound_order(page) == HPAGE_PMD_ORDER) {
/* cannot split THP, skip it */
if (!can_split_huge_page(page, NULL))
goto activate_locked;
@@ -1254,14 +1268,17 @@ static unsigned int shrink_page_list(struct list_head *page_list,
* tail pages can be freed without IO.
*/
if (!compound_mapcount(page) &&
- split_huge_page_to_list(page,
- page_list))
+ split_huge_page_to_list(page,
+ page_list))
goto activate_locked;
}
+try_to_swap:
if (!add_to_swap(page)) {
if (!PageTransHuge(page))
goto activate_locked_split;
/* Fallback to swap normal pages */
+ VM_BUG_ON_PAGE(compound_order(page) != HPAGE_PMD_ORDER,
+ page);
if (split_huge_page_to_list(page,
page_list))
goto activate_locked;
@@ -1278,6 +1295,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
mapping = page_mapping(page);
}
} else if (unlikely(PageTransHuge(page))) {
+ VM_BUG_ON_PAGE(compound_order(page) != HPAGE_PMD_ORDER, page);
/* Split file THP */
if (split_huge_page_to_list(page, page_list))
goto keep_locked;
@@ -1303,9 +1321,12 @@ static unsigned int shrink_page_list(struct list_head *page_list,
enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;
bool was_swapbacked = PageSwapBacked(page);

- if (unlikely(PageTransHuge(page)))
- flags |= TTU_SPLIT_HUGE_PMD;
-
+ if (unlikely(PageTransHuge(page))) {
+ if (compound_order(page) == HPAGE_PMD_ORDER)
+ flags |= TTU_SPLIT_HUGE_PMD;
+ else if (compound_order(page) == HPAGE_PUD_ORDER)
+ flags |= TTU_SPLIT_HUGE_PUD;
+ }
if (!try_to_unmap(page, flags)) {
stat->nr_unmap_fail += nr_pages;
if (!was_swapbacked && PageSwapBacked(page))
--
2.28.0
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