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>

2 files changed, 34 insertions, 23 deletions

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 830d47d5ca41..04f58acda8e8 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -13,7 +13,7 @@
         EM( SCAN_EXCEED_NONE_PTE,       "exceed_none_pte")              \
         EM( SCAN_PTE_NON_PRESENT,       "pte_non_present")              \
         EM( SCAN_PAGE_RO,               "no_writable_page")             \
-        EM( SCAN_NO_REFERENCED_PAGE,    "no_referenced_page")           \
+        EM( SCAN_LACK_REFERENCED_PAGE,  "lack_referenced_page")         \
         EM( SCAN_PAGE_NULL,             "page_null")                    \
         EM( SCAN_SCAN_ABORT,            "scan_aborted")                 \
         EM( SCAN_PAGE_COUNT,            "not_suitable_page_count")      \
@@ -47,7 +47,7 @@ SCAN_STATUS
 TRACE_EVENT(mm_khugepaged_scan_pmd,
 
         TP_PROTO(struct mm_struct *mm, struct page *page, bool writable,
-                 bool referenced, int none_or_zero, int status, int unmapped),
+                 int referenced, int none_or_zero, int status, int unmapped),
 
         TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped),
 
@@ -55,7 +55,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
                 __field(struct mm_struct *, mm)
                 __field(unsigned long, pfn)
                 __field(bool, writable)
-                __field(bool, referenced)
+                __field(int, referenced)
                 __field(int, none_or_zero)
                 __field(int, status)
                 __field(int, unmapped)
@@ -108,14 +108,14 @@ TRACE_EVENT(mm_collapse_huge_page,
 TRACE_EVENT(mm_collapse_huge_page_isolate,
 
         TP_PROTO(struct page *page, int none_or_zero,
-                 bool referenced, bool  writable, int status),
+                 int referenced, bool  writable, int status),
 
         TP_ARGS(page, none_or_zero, referenced, writable, status),
 
         TP_STRUCT__entry(
                 __field(unsigned long, pfn)
                 __field(int, none_or_zero)
-                __field(bool, referenced)
+                __field(int, referenced)
                 __field(bool, writable)
                 __field(int, status)
         ),
@@ -138,25 +138,28 @@ TRACE_EVENT(mm_collapse_huge_page_isolate,
 
 TRACE_EVENT(mm_collapse_huge_page_swapin,
 
-        TP_PROTO(struct mm_struct *mm, int swapped_in, int ret),
+        TP_PROTO(struct mm_struct *mm, int swapped_in, int referenced, int ret),
 
-        TP_ARGS(mm, swapped_in, ret),
+        TP_ARGS(mm, swapped_in, referenced, ret),
 
         TP_STRUCT__entry(
                 __field(struct mm_struct *, mm)
                 __field(int, swapped_in)
+                __field(int, referenced)
                 __field(int, ret)
         ),
 
         TP_fast_assign(
                 __entry->mm = mm;
                 __entry->swapped_in = swapped_in;
+                __entry->referenced = referenced;
                 __entry->ret = ret;
         ),
 
-        TP_printk("mm=%p, swapped_in=%d, ret=%d",
+        TP_printk("mm=%p, swapped_in=%d, referenced=%d, ret=%d",
                 __entry->mm,
                 __entry->swapped_in,
+                __entry->referenced,
                 __entry->ret)
 );
 
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,