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>

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 830d47d..04f58ac 100644 (file)
--- 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 5661484..7dbee69 100644 (file)
--- 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,