[RFC 3/7] mm: introduce MADV_COLD

[Minchan Kim]

When a process expects no accesses to a certain memory range
for a long time, it could hint kernel that the pages can be
reclaimed instantly but data should be preserved for future use.
This could reduce workingset eviction so it ends up increasing
performance.

This patch introduces the new MADV_COLD hint to madvise(2)
syscall. MADV_COLD can be used by a process to mark a memory range
as not expected to be used for a long time. The hint can help
kernel in deciding which pages to evict proactively.

Internally, it works via reclaiming memory in process context
the syscall is called. If the page is dirty but backing storage
is not synchronous device, the written page will be rotate back
into LRU's tail once the write is done so they will reclaim easily
when memory pressure happens. If backing storage is
synchrnous device(e.g., zram), hte page will be reclaimed instantly.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 include/linux/swap.h                   |   1 +
 include/uapi/asm-generic/mman-common.h |   1 +
 mm/madvise.c                           | 123 +++++++++++++++++++++++++
 mm/vmscan.c                            |  74 +++++++++++++++
 4 files changed, 199 insertions(+)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 64795abea003..7f32a948fc6a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -365,6 +365,7 @@ extern int vm_swappiness;
 extern int remove_mapping(struct address_space *mapping, struct page *page);
 extern unsigned long vm_total_pages;
 
+extern unsigned long reclaim_pages(struct list_head *page_list);
 #ifdef CONFIG_NUMA
 extern int node_reclaim_mode;
 extern int sysctl_min_unmapped_ratio;
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index f7a4a5d4b642..b9b51eeb8e1a 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -43,6 +43,7 @@
 #define MADV_WILLNEED	3		/* will need these pages */
 #define MADV_DONTNEED	4		/* don't need these pages */
 #define MADV_COOL	5		/* deactivatie these pages */
+#define MADV_COLD	6		/* reclaim these pages */
 
 /* common parameters: try to keep these consistent across architectures */
 #define MADV_FREE	8		/* free pages only if memory pressure */
diff --git a/mm/madvise.c b/mm/madvise.c
index c05817fb570d..9a6698b56845 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -42,6 +42,7 @@ static int madvise_need_mmap_write(int behavior)
 	case MADV_WILLNEED:
 	case MADV_DONTNEED:
 	case MADV_COOL:
+	case MADV_COLD:
 	case MADV_FREE:
 		return 0;
 	default:
@@ -416,6 +417,125 @@ static long madvise_cool(struct vm_area_struct *vma,
 	return 0;
 }
 
+static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
+				unsigned long end, struct mm_walk *walk)
+{
+	pte_t *orig_pte, *pte, ptent;
+	spinlock_t *ptl;
+	LIST_HEAD(page_list);
+	struct page *page;
+	int isolated = 0;
+	struct vm_area_struct *vma = walk->vma;
+	unsigned long next;
+
+	next = pmd_addr_end(addr, end);
+	if (pmd_trans_huge(*pmd)) {
+		spinlock_t *ptl;
+
+		ptl = pmd_trans_huge_lock(pmd, vma);
+		if (!ptl)
+			return 0;
+
+		if (is_huge_zero_pmd(*pmd))
+			goto huge_unlock;
+
+		page = pmd_page(*pmd);
+		if (page_mapcount(page) > 1)
+			goto huge_unlock;
+
+		if (next - addr != HPAGE_PMD_SIZE) {
+			int err;
+
+			get_page(page);
+			spin_unlock(ptl);
+			lock_page(page);
+			err = split_huge_page(page);
+			unlock_page(page);
+			put_page(page);
+			if (!err)
+				goto regular_page;
+			return 0;
+		}
+
+		if (isolate_lru_page(page))
+			goto huge_unlock;
+
+		list_add(&page->lru, &page_list);
+huge_unlock:
+		spin_unlock(ptl);
+		reclaim_pages(&page_list);
+		return 0;
+	}
+
+	if (pmd_trans_unstable(pmd))
+		return 0;
+regular_page:
+	orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	for (pte = orig_pte; addr < end; pte++, addr += PAGE_SIZE) {
+		ptent = *pte;
+		if (!pte_present(ptent))
+			continue;
+
+		page = vm_normal_page(vma, addr, ptent);
+		if (!page)
+			continue;
+
+		if (page_mapcount(page) > 1)
+			continue;
+
+		if (isolate_lru_page(page))
+			continue;
+
+		isolated++;
+		list_add(&page->lru, &page_list);
+		if (isolated >= SWAP_CLUSTER_MAX) {
+			pte_unmap_unlock(orig_pte, ptl);
+			reclaim_pages(&page_list);
+			isolated = 0;
+			pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+			orig_pte = pte;
+		}
+	}
+
+	pte_unmap_unlock(orig_pte, ptl);
+	reclaim_pages(&page_list);
+	cond_resched();
+
+	return 0;
+}
+
+static void madvise_cold_page_range(struct mmu_gather *tlb,
+			     struct vm_area_struct *vma,
+			     unsigned long addr, unsigned long end)
+{
+	struct mm_walk warm_walk = {
+		.pmd_entry = madvise_cold_pte_range,
+		.mm = vma->vm_mm,
+	};
+
+	tlb_start_vma(tlb, vma);
+	walk_page_range(addr, end, &warm_walk);
+	tlb_end_vma(tlb, vma);
+}
+
+
+static long madvise_cold(struct vm_area_struct *vma,
+			unsigned long start_addr, unsigned long end_addr)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct mmu_gather tlb;
+
+	if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
+		return -EINVAL;
+
+	lru_add_drain();
+	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
+	madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
+	tlb_finish_mmu(&tlb, start_addr, end_addr);
+
+	return 0;
+}
+
 static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 				unsigned long end, struct mm_walk *walk)
 
@@ -806,6 +926,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 		return madvise_willneed(vma, prev, start, end);
 	case MADV_COOL:
 		return madvise_cool(vma, start, end);
+	case MADV_COLD:
+		return madvise_cold(vma, start, end);
 	case MADV_FREE:
 	case MADV_DONTNEED:
 		return madvise_dontneed_free(vma, prev, start, end, behavior);
@@ -828,6 +950,7 @@ madvise_behavior_valid(int behavior)
 	case MADV_DONTNEED:
 	case MADV_FREE:
 	case MADV_COOL:
+	case MADV_COLD:
 #ifdef CONFIG_KSM
 	case MADV_MERGEABLE:
 	case MADV_UNMERGEABLE:
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a28e5d17b495..1701b31f70a8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2096,6 +2096,80 @@ static void shrink_active_list(unsigned long nr_to_scan,
 			nr_deactivate, nr_rotated, sc->priority, file);
 }
 
+unsigned long reclaim_pages(struct list_head *page_list)
+{
+	int nid = -1;
+	unsigned long nr_isolated[2] = {0, };
+	unsigned long nr_reclaimed = 0;
+	LIST_HEAD(node_page_list);
+	struct reclaim_stat dummy_stat;
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+		.priority = DEF_PRIORITY,
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+	};
+
+	while (!list_empty(page_list)) {
+		struct page *page;
+
+		page = lru_to_page(page_list);
+		list_del(&page->lru);
+
+		if (nid == -1) {
+			nid = page_to_nid(page);
+			INIT_LIST_HEAD(&node_page_list);
+			nr_isolated[0] = nr_isolated[1] = 0;
+		}
+
+		if (nid == page_to_nid(page)) {
+			list_add(&page->lru, &node_page_list);
+			nr_isolated[!!page_is_file_cache(page)] +=
+						hpage_nr_pages(page);
+			continue;
+		}
+
+		nid = page_to_nid(page);
+
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
+					nr_isolated[0]);
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
+					nr_isolated[1]);
+		nr_reclaimed += shrink_page_list(&node_page_list,
+				NODE_DATA(nid), &sc, TTU_IGNORE_ACCESS,
+				&dummy_stat, true);
+		while (!list_empty(&node_page_list)) {
+			struct page *page = lru_to_page(page_list);
+
+			list_del(&page->lru);
+			putback_lru_page(page);
+		}
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
+					-nr_isolated[0]);
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
+					-nr_isolated[1]);
+		nr_isolated[0] = nr_isolated[1] = 0;
+		INIT_LIST_HEAD(&node_page_list);
+	}
+
+	if (!list_empty(&node_page_list)) {
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
+					nr_isolated[0]);
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
+					nr_isolated[1]);
+		nr_reclaimed += shrink_page_list(&node_page_list,
+				NODE_DATA(nid), &sc, TTU_IGNORE_ACCESS,
+				&dummy_stat, true);
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
+					-nr_isolated[0]);
+		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
+					-nr_isolated[1]);
+	}
+
+	return nr_reclaimed;
+}
+
 /*
  * The inactive anon list should be small enough that the VM never has
  * to do too much work.
-- 
2.21.0.1020.gf2820cf01a-goog