mm, thp: convert from optimistic swapin collapsing to conservative

To detect whether khugepaged swapin is worthwhile, this patch checks the
amount of young pages.  There should be at least half of HPAGE_PMD_NR to
swapin.

Link: http://lkml.kernel.org/r/1468109451-1615-1-git-send-email-ebru.akagunduz@gmail.com
Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 15 deletions

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 566148489e33..7dbee698d6aa 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -27,7 +27,7 @@ enum scan_result {
 	SCAN_EXCEED_NONE_PTE,
 	SCAN_PTE_NON_PRESENT,
 	SCAN_PAGE_RO,
-	SCAN_NO_REFERENCED_PAGE,
+	SCAN_LACK_REFERENCED_PAGE,
 	SCAN_PAGE_NULL,
 	SCAN_SCAN_ABORT,
 	SCAN_PAGE_COUNT,
@@ -500,8 +500,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 {
 	struct page *page = NULL;
 	pte_t *_pte;
-	int none_or_zero = 0, result = 0;
-	bool referenced = false, writable = false;
+	int none_or_zero = 0, result = 0, referenced = 0;
+	bool writable = false;
 
 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 	     _pte++, address += PAGE_SIZE) {
@@ -580,11 +580,11 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		VM_BUG_ON_PAGE(!PageLocked(page), page);
 		VM_BUG_ON_PAGE(PageLRU(page), page);
 
-		/* If there is no mapped pte young don't collapse the page */
+		/* There should be enough young pte to collapse the page */
 		if (pte_young(pteval) ||
 		    page_is_young(page) || PageReferenced(page) ||
 		    mmu_notifier_test_young(vma->vm_mm, address))
-			referenced = true;
+			referenced++;
 	}
 	if (likely(writable)) {
 		if (likely(referenced)) {
@@ -869,7 +869,8 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address)
 
 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 					struct vm_area_struct *vma,
-					unsigned long address, pmd_t *pmd)
+					unsigned long address, pmd_t *pmd,
+					int referenced)
 {
 	pte_t pteval;
 	int swapped_in = 0, ret = 0;
@@ -887,12 +888,19 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 		if (!is_swap_pte(pteval))
 			continue;
 		swapped_in++;
+		/* we only decide to swapin, if there is enough young ptes */
+		if (referenced < HPAGE_PMD_NR/2) {
+			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+			return false;
+		}
 		ret = do_swap_page(&fe, pteval);
+
 		/* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
 		if (ret & VM_FAULT_RETRY) {
 			down_read(&mm->mmap_sem);
 			if (hugepage_vma_revalidate(mm, address)) {
 				/* vma is no longer available, don't continue to swapin */
+				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 				return false;
 			}
 			/* check if the pmd is still valid */
@@ -900,7 +908,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 				return false;
 		}
 		if (ret & VM_FAULT_ERROR) {
-			trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
+			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 			return false;
 		}
 		/* pte is unmapped now, we need to map it */
@@ -908,7 +916,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 	}
 	fe.pte--;
 	pte_unmap(fe.pte);
-	trace_mm_collapse_huge_page_swapin(mm, swapped_in, 1);
+	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 	return true;
 }
 
@@ -916,7 +924,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 				   unsigned long address,
 				   struct page **hpage,
 				   struct vm_area_struct *vma,
-				   int node)
+				   int node, int referenced)
 {
 	pmd_t *pmd, _pmd;
 	pte_t *pte;
@@ -973,7 +981,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 * If it fails, we release mmap_sem and jump out_nolock.
 	 * Continuing to collapse causes inconsistency.
 	 */
-	if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) {
+	if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
 		mem_cgroup_cancel_charge(new_page, memcg, true);
 		up_read(&mm->mmap_sem);
 		goto out_nolock;
@@ -1084,12 +1092,12 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 {
 	pmd_t *pmd;
 	pte_t *pte, *_pte;
-	int ret = 0, none_or_zero = 0, result = 0;
+	int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
 	struct page *page = NULL;
 	unsigned long _address;
 	spinlock_t *ptl;
 	int node = NUMA_NO_NODE, unmapped = 0;
-	bool writable = false, referenced = false;
+	bool writable = false;
 
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 
@@ -1177,14 +1185,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 		if (pte_young(pteval) ||
 		    page_is_young(page) || PageReferenced(page) ||
 		    mmu_notifier_test_young(vma->vm_mm, address))
-			referenced = true;
+			referenced++;
 	}
 	if (writable) {
 		if (referenced) {
 			result = SCAN_SUCCEED;
 			ret = 1;
 		} else {
-			result = SCAN_NO_REFERENCED_PAGE;
+			result = SCAN_LACK_REFERENCED_PAGE;
 		}
 	} else {
 		result = SCAN_PAGE_RO;
@@ -1194,7 +1202,7 @@ out_unmap:
 	if (ret) {
 		node = khugepaged_find_target_node();
 		/* collapse_huge_page will return with the mmap_sem released */
-		collapse_huge_page(mm, address, hpage, vma, node);
+		collapse_huge_page(mm, address, hpage, vma, node, referenced);
 	}
 out:
 	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,