mm/vmscan: protect the workingset on anonymous LRU

In current implementation, newly created or swap-in anonymous page is
started on active list.  Growing active list results in rebalancing
active/inactive list so old pages on active list are demoted to inactive
list.  Hence, the page on active list isn't protected at all.

Following is an example of this situation.

Assume that 50 hot pages on active list.  Numbers denote the number of
pages on active/inactive list (active | inactive).

1. 50 hot pages on active list
50(h) | 0

2. workload: 50 newly created (used-once) pages
50(uo) | 50(h)

3. workload: another 50 newly created (used-once) pages
50(uo) | 50(uo), swap-out 50(h)

This patch tries to fix this issue.  Like as file LRU, newly created or
swap-in anonymous pages will be inserted to the inactive list.  They are
promoted to active list if enough reference happens.  This simple
modification changes the above example as following.

1. 50 hot pages on active list
50(h) | 0

2. workload: 50 newly created (used-once) pages
50(h) | 50(uo)

3. workload: another 50 newly created (used-once) pages
50(h) | 50(uo), swap-out 50(uo)

As you can see, hot pages on active list would be protected.

Note that, this implementation has a drawback that the page cannot be
promoted and will be swapped-out if re-access interval is greater than the
size of inactive list but less than the size of total(active+inactive).
To solve this potential issue, following patch will apply workingset
detection similar to the one that's already applied to file LRU.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Link: http://lkml.kernel.org/r/1595490560-15117-3-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 17 insertions, 19 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 206f52b36ffb..863c495776d7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -640,7 +640,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 		entry = mk_huge_pmd(page, vma->vm_page_prot);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 		page_add_new_anon_rmap(page, vma, haddr, true);
-		lru_cache_add_active_or_unevictable(page, vma);
+		lru_cache_add_inactive_or_unevictable(page, vma);
 		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
 		set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
 		add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b52bd46ad146..15a9af791014 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1173,7 +1173,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	spin_lock(pmd_ptl);
 	BUG_ON(!pmd_none(*pmd));
 	page_add_new_anon_rmap(new_page, vma, address, true);
-	lru_cache_add_active_or_unevictable(new_page, vma);
+	lru_cache_add_inactive_or_unevictable(new_page, vma);
 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
 	set_pmd_at(mm, address, pmd, _pmd);
 	update_mmu_cache_pmd(vma, address, pmd);
diff --git a/mm/memory.c b/mm/memory.c
index c39a13b09602..6fe8b5b22c57 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2715,7 +2715,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		 */
 		ptep_clear_flush_notify(vma, vmf->address, vmf->pte);
 		page_add_new_anon_rmap(new_page, vma, vmf->address, false);
-		lru_cache_add_active_or_unevictable(new_page, vma);
+		lru_cache_add_inactive_or_unevictable(new_page, vma);
 		/*
 		 * We call the notify macro here because, when using secondary
 		 * mmu page tables (such as kvm shadow page tables), we want the
@@ -3266,10 +3266,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	/* ksm created a completely new copy */
 	if (unlikely(page != swapcache && swapcache)) {
 		page_add_new_anon_rmap(page, vma, vmf->address, false);
-		lru_cache_add_active_or_unevictable(page, vma);
+		lru_cache_add_inactive_or_unevictable(page, vma);
 	} else {
 		do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
-		activate_page(page);
 	}
 
 	swap_free(entry);
@@ -3414,7 +3413,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 
 	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, vma, vmf->address, false);
-	lru_cache_add_active_or_unevictable(page, vma);
+	lru_cache_add_inactive_or_unevictable(page, vma);
 setpte:
 	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
 
@@ -3672,7 +3671,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct page *page)
 	if (write && !(vma->vm_flags & VM_SHARED)) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 		page_add_new_anon_rmap(page, vma, vmf->address, false);
-		lru_cache_add_active_or_unevictable(page, vma);
+		lru_cache_add_inactive_or_unevictable(page, vma);
 	} else {
 		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
 		page_add_file_rmap(page, false);
diff --git a/mm/migrate.c b/mm/migrate.c
index d179657f8685..819e55130134 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2830,7 +2830,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 	inc_mm_counter(mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, vma, addr, false);
 	if (!is_zone_device_page(page))
-		lru_cache_add_active_or_unevictable(page, vma);
+		lru_cache_add_inactive_or_unevictable(page, vma);
 	get_page(page);
 
 	if (flush) {
diff --git a/mm/swap.c b/mm/swap.c
index de257c0a89b1..9285e60c7d6e 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -476,23 +476,24 @@ void lru_cache_add(struct page *page)
 EXPORT_SYMBOL(lru_cache_add);
 
 /**
- * lru_cache_add_active_or_unevictable
+ * lru_cache_add_inactive_or_unevictable
  * @page:  the page to be added to LRU
  * @vma:   vma in which page is mapped for determining reclaimability
  *
- * Place @page on the active or unevictable LRU list, depending on its
+ * Place @page on the inactive or unevictable LRU list, depending on its
  * evictability.  Note that if the page is not evictable, it goes
  * directly back onto it's zone's unevictable list, it does NOT use a
  * per cpu pagevec.
  */
-void lru_cache_add_active_or_unevictable(struct page *page,
+void lru_cache_add_inactive_or_unevictable(struct page *page,
 					 struct vm_area_struct *vma)
 {
+	bool unevictable;
+
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 
-	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
-		SetPageActive(page);
-	else if (!TestSetPageMlocked(page)) {
+	unevictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED;
+	if (unlikely(unevictable) && !TestSetPageMlocked(page)) {
 		/*
 		 * We use the irq-unsafe __mod_zone_page_stat because this
 		 * counter is not modified from interrupt context, and the pte
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6c26916e95fd..82183432fdd0 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1915,7 +1915,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		page_add_anon_rmap(page, vma, addr, false);
 	} else { /* ksm created a completely new copy */
 		page_add_new_anon_rmap(page, vma, addr, false);
-		lru_cache_add_active_or_unevictable(page, vma);
+		lru_cache_add_inactive_or_unevictable(page, vma);
 	}
 	swap_free(entry);
 	/*
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index b80419320c7d..9a3d451402d7 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -123,7 +123,7 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 
 	inc_mm_counter(dst_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
-	lru_cache_add_active_or_unevictable(page, dst_vma);
+	lru_cache_add_inactive_or_unevictable(page, dst_vma);
 
 	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e34fc04b7045..783cd7fdc61a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -998,8 +998,6 @@ static enum page_references page_check_references(struct page *page,
 		return PAGEREF_RECLAIM;
 
 	if (referenced_ptes) {
-		if (PageSwapBacked(page))
-			return PAGEREF_ACTIVATE;
 		/*
 		 * All mapped pages start out with page table
 		 * references from the instantiating fault, so we need
@@ -1022,7 +1020,7 @@ static enum page_references page_check_references(struct page *page,
 		/*
 		 * Activate file-backed executable pages after first usage.
 		 */
-		if (vm_flags & VM_EXEC)
+		if ((vm_flags & VM_EXEC) && !PageSwapBacked(page))
 			return PAGEREF_ACTIVATE;
 
 		return PAGEREF_KEEP;