[PATCH -mm -V2 17/21] mm, THP, swap: Support PMD swap mapping for MADV_WILLNEED

["Huang, Ying" <ying.huang@intel.com>]

From: Huang Ying <ying.huang@intel.com>

During MADV_WILLNEED, for a PMD swap mapping, if THP swapin is enabled
for the VMA, the whole swap cluster will be swapin.  Otherwise, the
huge swap cluster and the PMD swap mapping will be split and fallback
to PTE swap mapping.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
---
 mm/madvise.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index e03e85a20fb4..44a0a62f4848 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -196,14 +196,36 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
 	pte_t *orig_pte;
 	struct vm_area_struct *vma = walk->private;
 	unsigned long index;
+	swp_entry_t entry;
+	struct page *page;
+	pmd_t pmdval;
+
+	pmdval = *pmd;
+	if (thp_swap_supported() && is_swap_pmd(pmdval) &&
+	    !is_pmd_migration_entry(pmdval)) {
+		entry = pmd_to_swp_entry(pmdval);
+		if (!transparent_hugepage_swapin_enabled(vma)) {
+			if (!split_swap_cluster(entry, false))
+				split_huge_swap_pmd(vma, pmd, start, pmdval);
+		} else {
+			page = read_swap_cache_async(entry,
+						     GFP_HIGHUSER_MOVABLE,
+						     vma, start, false);
+			/* The swap cluster has been split under us */
+			if (page) {
+				if (!PageTransHuge(page))
+					split_huge_swap_pmd(vma, pmd, start,
+							    pmdval);
+				put_page(page);
+			}
+		}
+	}
 
 	if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 		return 0;
 
 	for (index = start; index != end; index += PAGE_SIZE) {
 		pte_t pte;
-		swp_entry_t entry;
-		struct page *page;
 		spinlock_t *ptl;
 
 		orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
-- 
2.16.1