khugepaged: allow to collapse PTE-mapped compound pages

We can collapse PTE-mapped compound pages.  We only need to avoid handling
them more than once: lock/unlock page only once if it's present in the PMD
range multiple times as it handled on compound level.  The same goes for
LRU isolation and putback.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200416160026.16538-7-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 71ee91d..1bae663 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -512,17 +512,30 @@ void __khugepaged_exit(struct mm_struct *mm)
 
 static void release_pte_page(struct page *page)
 {
-       dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_lru(page));
+       mod_node_page_state(page_pgdat(page),
+                       NR_ISOLATED_ANON + page_is_file_lru(page),
+                       -compound_nr(page));
        unlock_page(page);
        putback_lru_page(page);
 }
 
-static void release_pte_pages(pte_t *pte, pte_t *_pte)
+static void release_pte_pages(pte_t *pte, pte_t *_pte,
+               struct list_head *compound_pagelist)
 {
+       struct page *page, *tmp;
+
        while (--_pte >= pte) {
                pte_t pteval = *_pte;
-               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
-                       release_pte_page(pte_page(pteval));
+
+               page = pte_page(pteval);
+               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
+                               !PageCompound(page))
+                       release_pte_page(page);
+       }
+
+       list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
+               list_del(&page->lru);
+               release_pte_page(page);
        }
 }
 
@@ -539,7 +552,8 @@ static bool is_refcount_suitable(struct page *page)
 
 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
                                        unsigned long address,
-                                       pte_t *pte)
+                                       pte_t *pte,
+                                       struct list_head *compound_pagelist)
 {
        struct page *page = NULL;
        pte_t *_pte;
@@ -569,13 +583,21 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
                        goto out;
                }
 
-               /* TODO: teach khugepaged to collapse THP mapped with pte */
+               VM_BUG_ON_PAGE(!PageAnon(page), page);
+
                if (PageCompound(page)) {
-                       result = SCAN_PAGE_COMPOUND;
-                       goto out;
-               }
+                       struct page *p;
+                       page = compound_head(page);
 
-               VM_BUG_ON_PAGE(!PageAnon(page), page);
+                       /*
+                        * Check if we have dealt with the compound page
+                        * already
+                        */
+                       list_for_each_entry(p, compound_pagelist, lru) {
+                               if (page == p)
+                                       goto next;
+                       }
+               }
 
                /*
                 * We can do it before isolate_lru_page because the
@@ -604,19 +626,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
                        result = SCAN_PAGE_COUNT;
                        goto out;
                }
-               if (pte_write(pteval)) {
-                       writable = true;
-               } else {
-                       if (PageSwapCache(page) &&
-                           !reuse_swap_page(page, NULL)) {
-                               unlock_page(page);
-                               result = SCAN_SWAP_CACHE_PAGE;
-                               goto out;
-                       }
+               if (!pte_write(pteval) && PageSwapCache(page) &&
+                               !reuse_swap_page(page, NULL)) {
                        /*
-                        * Page is not in the swap cache. It can be collapsed
-                        * into a THP.
+                        * Page is in the swap cache and cannot be re-used.
+                        * It cannot be collapsed into a THP.
                         */
+                       unlock_page(page);
+                       result = SCAN_SWAP_CACHE_PAGE;
+                       goto out;
                }
 
                /*
@@ -628,16 +646,23 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
                        result = SCAN_DEL_PAGE_LRU;
                        goto out;
                }
-               inc_node_page_state(page,
-                               NR_ISOLATED_ANON + page_is_file_lru(page));
+               mod_node_page_state(page_pgdat(page),
+                               NR_ISOLATED_ANON + page_is_file_lru(page),
+                               compound_nr(page));
                VM_BUG_ON_PAGE(!PageLocked(page), page);
                VM_BUG_ON_PAGE(PageLRU(page), page);
 
+               if (PageCompound(page))
+                       list_add_tail(&page->lru, compound_pagelist);
+next:
                /* 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++;
+
+               if (pte_write(pteval))
+                       writable = true;
        }
        if (likely(writable)) {
                if (likely(referenced)) {
@@ -651,7 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
        }
 
 out:
-       release_pte_pages(pte, _pte);
+       release_pte_pages(pte, _pte, compound_pagelist);
        trace_mm_collapse_huge_page_isolate(page, none_or_zero,
                                            referenced, writable, result);
        return 0;
@@ -660,13 +685,14 @@ out:
 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
                                      struct vm_area_struct *vma,
                                      unsigned long address,
-                                     spinlock_t *ptl)
+                                     spinlock_t *ptl,
+                                     struct list_head *compound_pagelist)
 {
+       struct page *src_page, *tmp;
        pte_t *_pte;
        for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
                                _pte++, page++, address += PAGE_SIZE) {
                pte_t pteval = *_pte;
-               struct page *src_page;
 
                if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
                        clear_user_highpage(page, address);
@@ -686,7 +712,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
                } else {
                        src_page = pte_page(pteval);
                        copy_user_highpage(page, src_page, address, vma);
-                       release_pte_page(src_page);
+                       if (!PageCompound(src_page))
+                               release_pte_page(src_page);
                        /*
                         * ptl mostly unnecessary, but preempt has to
                         * be disabled to update the per-cpu stats
@@ -703,6 +730,11 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
                        free_page_and_swap_cache(src_page);
                }
        }
+
+       list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
+               list_del(&src_page->lru);
+               release_pte_page(src_page);
+       }
 }
 
 static void khugepaged_alloc_sleep(void)
@@ -961,6 +993,7 @@ static void collapse_huge_page(struct mm_struct *mm,
                                   struct page **hpage,
                                   int node, int referenced, int unmapped)
 {
+       LIST_HEAD(compound_pagelist);
        pmd_t *pmd, _pmd;
        pte_t *pte;
        pgtable_t pgtable;
@@ -1061,7 +1094,8 @@ static void collapse_huge_page(struct mm_struct *mm,
        mmu_notifier_invalidate_range_end(&range);
 
        spin_lock(pte_ptl);
-       isolated = __collapse_huge_page_isolate(vma, address, pte);
+       isolated = __collapse_huge_page_isolate(vma, address, pte,
+                       &compound_pagelist);
        spin_unlock(pte_ptl);
 
        if (unlikely(!isolated)) {
@@ -1086,7 +1120,8 @@ static void collapse_huge_page(struct mm_struct *mm,
         */
        anon_vma_unlock_write(vma->anon_vma);
 
-       __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
+       __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
+                       &compound_pagelist);
        pte_unmap(pte);
        __SetPageUptodate(new_page);
        pgtable = pmd_pgtable(_pmd);
@@ -1205,11 +1240,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
                        goto out_unmap;
                }
 
-               /* TODO: teach khugepaged to collapse THP mapped with pte */
-               if (PageCompound(page)) {
-                       result = SCAN_PAGE_COMPOUND;
-                       goto out_unmap;
-               }
+               page = compound_head(page);
 
                /*
                 * Record which node the original page is from and save this