mm: reclaim MADV_FREE pages

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

[minchan@kernel.org: clean up lazyfree page handling]
  Link: http://lkml.kernel.org/r/20170303025237.GB3503@bbox
Link: http://lkml.kernel.org/r/14b8eb1d3f6bf6cc492833f183ac8c304e560484.1487965799.git.shli@fb.com
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 26 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index b4084d09dbe8..519b7eb723d1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1288,11 +1288,6 @@ 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
  */
@@ -1308,8 +1303,7 @@ 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))
@@ -1427,11 +1421,21 @@ 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)) {
-				/* It's a freeable page by MADV_FREE */
-				dec_mm_counter(mm, MM_ANONPAGES);
-				rp->lazyfreed++;
-				goto discard;
+			/* MADV_FREE page check */
+			if (!PageSwapBacked(page)) {
+				if (!PageDirty(page)) {
+					dec_mm_counter(mm, MM_ANONPAGES);
+					goto discard;
+				}
+
+				/*
+				 * If the page was redirtied, it cannot be
+				 * discarded. Remap the page to page table.
+				 */
+				set_pte_at(mm, address, pvmw.pte, pteval);
+				ret = SWAP_DIRTY;
+				page_vma_mapped_walk_done(&pvmw);
+				break;
 			}
 
 			if (swap_duplicate(entry) < 0) {
@@ -1499,18 +1503,15 @@ 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,
 	};
@@ -1531,11 +1532,8 @@ 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;
 }
 
@@ -1562,14 +1560,10 @@ 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,