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Subject[RFC PATCH 20/31] mm: thp: split 1GB THPs at page reclaim.
Date
From: Zi Yan <ziy@nvidia.com>

We cannot swap 1GB THPs, so split them before swap them out.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
mm/swap_slots.c | 2 ++
mm/vmscan.c | 55 ++++++++++++++++++++++++++++++++++++-------------
2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 63a7b4563a57..797c804ff905 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -315,6 +315,8 @@ 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 a714c4f800e9..a2a91c1d3dae 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1288,25 +1288,47 @@ static unsigned long shrink_page_list(struct list_head *page_list,
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
if (PageTransHuge(page)) {
- /* cannot split THP, skip it */
- if (!can_split_huge_page(page, NULL))
- goto activate_locked;
- /*
- * Split pages without a PMD map right
- * away. Chances are some or all of the
- * tail pages can be freed without IO.
- */
- if (!compound_mapcount(page) &&
- split_huge_page_to_list(page,
- page_list))
+ if (compound_order(page) == HPAGE_PUD_ORDER) {
+ /* cannot split THP, skip it */
+ if (!can_split_huge_pud_page(page, NULL))
+ goto activate_locked;
+ /*
+ * Split pages without a PMD map right
+ * away. Chances are some or all of the
+ * tail pages can be freed without IO.
+ */
+ if (!compound_mapcount(page) &&
+ split_huge_pud_page_to_list(page,
+ page_list))
+ goto activate_locked;
+ }
+ if (compound_order(page) == HPAGE_PMD_ORDER) {
+ /* cannot split THP, skip it */
+ if (!can_split_huge_page(page, NULL))
+ goto activate_locked;
+ /*
+ * Split pages without a PMD map right
+ * away. Chances are some or all of the
+ * tail pages can be freed without IO.
+ */
+ if (!compound_mapcount(page) &&
+ split_huge_page_to_list(page,
+ page_list))
+ goto activate_locked;
+ }
+ }
+ if (compound_order(page) == HPAGE_PUD_ORDER) {
+ if (split_huge_pud_page_to_list(page,
+ page_list))
goto activate_locked;
}
if (!add_to_swap(page)) {
if (!PageTransHuge(page))
goto activate_locked;
/* 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))
+ page_list))
goto activate_locked;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
count_vm_event(THP_SWPOUT_FALLBACK);
@@ -1321,6 +1343,7 @@ static unsigned long 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;
@@ -1333,8 +1356,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
if (page_mapped(page)) {
enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;

- 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)) {
nr_unmap_fail++;
goto activate_locked;
--
2.20.1
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