[PATCH V5 4/6] mm: reclaim MADV_FREE pages

[Shaohua Li]

When memory pressure is high, we free MADV_FREE pages. If the pages are
not dirty in pte, the pages could be freed immediately. Otherwise we
can't reclaim them. We put the pages back to anonumous LRU list (by
setting SwapBacked flag) and the pages will be reclaimed in normal
swapout way.

We use normal page reclaim policy. Since MADV_FREE pages are put into
inactive file list, such pages and inactive file pages are reclaimed
according to their age. This is expected, because we don't want to
reclaim too many MADV_FREE pages before used once pages.

Based on Minchan's original patch

Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
---
 include/linux/rmap.h |  2 +-
 mm/huge_memory.c     |  2 ++
 mm/madvise.c         |  1 +
 mm/rmap.c            | 40 +++++++++++++++++-----------------------
 mm/vmscan.c          | 34 ++++++++++++++++++++++------------
 5 files changed, 43 insertions(+), 36 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 7a39414..fee10d7 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -298,6 +298,6 @@ static inline int page_mkclean(struct page *page)
 #define SWAP_AGAIN	1
 #define SWAP_FAIL	2
 #define SWAP_MLOCK	3
-#define SWAP_LZFREE	4
+#define SWAP_DIRTY	4
 
 #endif	/* _LINUX_RMAP_H */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3b7ee0c..4c7454b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1571,6 +1571,8 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		set_pmd_at(mm, addr, pmd, orig_pmd);
 		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
 	}
+
+	mark_page_lazyfree(page);
 	ret = true;
 out:
 	spin_unlock(ptl);
diff --git a/mm/madvise.c b/mm/madvise.c
index 61e10b1..225af7d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -413,6 +413,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 			set_pte_at(mm, addr, pte, ptent);
 			tlb_remove_tlb_entry(tlb, pte, addr);
 		}
+		mark_page_lazyfree(page);
 	}
 out:
 	if (nr_swap) {
diff --git a/mm/rmap.c b/mm/rmap.c
index c621088..bb45712 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1281,11 +1281,6 @@ void page_remove_rmap(struct page *page, bool compound)
 	 */
 }
 
-struct rmap_private {
-	enum ttu_flags flags;
-	int lazyfreed;
-};
-
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */
@@ -1301,8 +1296,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	pte_t pteval;
 	struct page *subpage;
 	int ret = SWAP_AGAIN;
-	struct rmap_private *rp = arg;
-	enum ttu_flags flags = rp->flags;
+	enum ttu_flags flags = (enum ttu_flags)arg;
 
 	/* munlock has nothing to gain from examining un-locked vmas */
 	if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
@@ -1419,11 +1413,21 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 			VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
 				page);
 
-			if (!PageDirty(page)) {
+			/*
+			 * swapin page could be clean, it has data stored in
+			 * swap. We can't silently discard it without setting
+			 * swap entry in the page table.
+			 */
+			if (!PageDirty(page) && !PageSwapCache(page)) {
 				/* It's a freeable page by MADV_FREE */
 				dec_mm_counter(mm, MM_ANONPAGES);
-				rp->lazyfreed++;
 				goto discard;
+			} else if (!PageSwapBacked(page)) {
+				/* dirty MADV_FREE page */
+				set_pte_at(mm, address, pvmw.pte, pteval);
+				ret = SWAP_DIRTY;
+				page_vma_mapped_walk_done(&pvmw);
+				break;
 			}
 
 			if (swap_duplicate(entry) < 0) {
@@ -1491,18 +1495,15 @@ static int page_mapcount_is_zero(struct page *page)
  * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
  * SWAP_MLOCK	- page is mlocked.
+ * SWAP_DIRTY	- page is dirty MADV_FREE page
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {
 	int ret;
-	struct rmap_private rp = {
-		.flags = flags,
-		.lazyfreed = 0,
-	};
 
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
-		.arg = &rp,
+		.arg = (void *)flags,
 		.done = page_mapcount_is_zero,
 		.anon_lock = page_lock_anon_vma_read,
 	};
@@ -1523,11 +1524,8 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
 	else
 		ret = rmap_walk(page, &rwc);
 
-	if (ret != SWAP_MLOCK && !page_mapcount(page)) {
+	if (ret != SWAP_MLOCK && !page_mapcount(page))
 		ret = SWAP_SUCCESS;
-		if (rp.lazyfreed && !PageDirty(page))
-			ret = SWAP_LZFREE;
-	}
 	return ret;
 }
 
@@ -1554,14 +1552,10 @@ static int page_not_mapped(struct page *page)
 int try_to_munlock(struct page *page)
 {
 	int ret;
-	struct rmap_private rp = {
-		.flags = TTU_MUNLOCK,
-		.lazyfreed = 0,
-	};
 
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
-		.arg = &rp,
+		.arg = (void *)TTU_MUNLOCK,
 		.done = page_not_mapped,
 		.anon_lock = page_lock_anon_vma_read,
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 68ea50d..16ad821 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -911,7 +911,8 @@ static void page_check_dirty_writeback(struct page *page,
 	 * Anonymous pages are not handled by flushers and must be written
 	 * from reclaim context. Do not stall reclaim based on them
 	 */
-	if (!page_is_file_cache(page)) {
+	if (!page_is_file_cache(page) ||
+	    (PageAnon(page) && !PageSwapBacked(page))) {
 		*dirty = false;
 		*writeback = false;
 		return;
@@ -992,7 +993,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			goto keep_locked;
 
 		/* Double the slab pressure for mapped and swapcache pages */
-		if (page_mapped(page) || PageSwapCache(page))
+		if ((page_mapped(page) || PageSwapCache(page)) &&
+		    !(PageAnon(page) && !PageSwapBacked(page)))
 			sc->nr_scanned++;
 
 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
@@ -1118,8 +1120,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		/*
 		 * Anonymous process memory has backing store?
 		 * Try to allocate it some swap space here.
+		 * Lazyfree page could be freed directly
 		 */
-		if (PageAnon(page) && !PageSwapCache(page)) {
+		if (PageAnon(page) && PageSwapBacked(page) &&
+		    !PageSwapCache(page)) {
 			if (!(sc->gfp_mask & __GFP_IO))
 				goto keep_locked;
 			if (!add_to_swap(page, page_list))
@@ -1140,9 +1144,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 * The page is mapped into the page tables of one or more
 		 * processes. Try to unmap it here.
 		 */
-		if (page_mapped(page) && mapping) {
+		if (page_mapped(page)) {
 			switch (ret = try_to_unmap(page,
 				ttu_flags | TTU_BATCH_FLUSH)) {
+			case SWAP_DIRTY:
+				SetPageSwapBacked(page);
+				/* fall through */
 			case SWAP_FAIL:
 				nr_unmap_fail++;
 				goto activate_locked;
@@ -1150,8 +1157,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				goto keep_locked;
 			case SWAP_MLOCK:
 				goto cull_mlocked;
-			case SWAP_LZFREE:
-				goto lazyfree;
 			case SWAP_SUCCESS:
 				; /* try to free the page below */
 			}
@@ -1263,10 +1268,18 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			}
 		}
 
-lazyfree:
-		if (!mapping || !__remove_mapping(mapping, page, true))
-			goto keep_locked;
+		if (PageAnon(page) && !PageSwapBacked(page)) {
+			/* follow __remove_mapping for reference */
+			if (!page_ref_freeze(page, 1))
+				goto keep_locked;
+			if (PageDirty(page)) {
+				page_ref_unfreeze(page, 1);
+				goto keep_locked;
+			}
 
+			count_vm_event(PGLAZYFREED);
+		} else if (!mapping || !__remove_mapping(mapping, page, true))
+			goto keep_locked;
 		/*
 		 * At this point, we have no other references and there is
 		 * no way to pick any more up (removed from LRU, removed
@@ -1276,9 +1289,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 */
 		__ClearPageLocked(page);
 free_it:
-		if (ret == SWAP_LZFREE)
-			count_vm_event(PGLAZYFREED);
-
 		nr_reclaimed++;
 
 		/*
-- 
2.9.3