[PATCH 20 of 28] split_huge_page paging

[Andrea Arcangeli <aarcange@redhat.com>]

From: Andrea Arcangeli <aarcange@redhat.com>

Paging logic that splits the page before it is unmapped and added to swap to
ensure backwards compatibility with the legacy swap code. Eventually swap
should natively pageout the hugepages to increase performance and decrease
seeking and fragmentation of swap space. swapoff can just skip over huge pmd as
they cannot be part of swap yet.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/rmap.c b/mm/rmap.c
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1176,6 +1176,10 @@ int try_to_unmap(struct page *page, enum
 
 	BUG_ON(!PageLocked(page));
 
+	if (unlikely(PageCompound(page)))
+		if (unlikely(split_huge_page(page)))
+			return SWAP_AGAIN;
+
 	if (unlikely(PageKsm(page)))
 		ret = try_to_unmap_ksm(page, flags);
 	else if (PageAnon(page))
diff --git a/mm/swap_state.c b/mm/swap_state.c
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -152,6 +152,10 @@ int add_to_swap(struct page *page)
 	VM_BUG_ON(!PageLocked(page));
 	VM_BUG_ON(!PageUptodate(page));
 
+	if (unlikely(PageCompound(page)))
+		if (unlikely(split_huge_page(page)))
+			return 0;
+
 	entry = get_swap_page();
 	if (!entry.val)
 		return 0;
diff --git a/mm/swapfile.c b/mm/swapfile.c
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -905,6 +905,8 @@ static inline int unuse_pmd_range(struct
 	pmd = pmd_offset(pud, addr);
 	do {
 		next = pmd_addr_end(addr, end);
+		if (unlikely(pmd_trans_huge(*pmd)))
+			continue;
 		if (pmd_none_or_clear_bad(pmd))
 			continue;
 		ret = unuse_pte_range(vma, pmd, addr, next, entry, page);

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