1 files changed, 62 insertions, 39 deletions

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 4b366d181f35..aee9b0b8d907 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -99,6 +99,7 @@ struct z3fold_header {
 #define NCHUNKS		((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
 
 #define BUDDY_MASK	(0x3)
+#define BUDDY_SHIFT	2
 
 /**
  * struct z3fold_pool - stores metadata for each z3fold pool
@@ -145,7 +146,7 @@ enum z3fold_page_flags {
 	MIDDLE_CHUNK_MAPPED,
 	NEEDS_COMPACTING,
 	PAGE_STALE,
-	UNDER_RECLAIM
+	PAGE_CLAIMED, /* by either reclaim or free */
 };
 
 /*****************
@@ -174,7 +175,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
 	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 	clear_bit(NEEDS_COMPACTING, &page->private);
 	clear_bit(PAGE_STALE, &page->private);
-	clear_bit(UNDER_RECLAIM, &page->private);
+	clear_bit(PAGE_CLAIMED, &page->private);
 
 	spin_lock_init(&zhdr->page_lock);
 	kref_init(&zhdr->refcount);
@@ -223,8 +224,11 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 	unsigned long handle;
 
 	handle = (unsigned long)zhdr;
-	if (bud != HEADLESS)
-		handle += (bud + zhdr->first_num) & BUDDY_MASK;
+	if (bud != HEADLESS) {
+		handle |= (bud + zhdr->first_num) & BUDDY_MASK;
+		if (bud == LAST)
+			handle |= (zhdr->last_chunks << BUDDY_SHIFT);
+	}
 	return handle;
 }
 
@@ -234,6 +238,12 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
 	return (struct z3fold_header *)(handle & PAGE_MASK);
 }
 
+/* only for LAST bud, returns zero otherwise */
+static unsigned short handle_to_chunks(unsigned long handle)
+{
+	return (handle & ~PAGE_MASK) >> BUDDY_SHIFT;
+}
+
 /*
  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
  *  but that doesn't matter. because the masking will result in the
@@ -720,37 +730,39 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 	page = virt_to_page(zhdr);
 
 	if (test_bit(PAGE_HEADLESS, &page->private)) {
-		/* HEADLESS page stored */
-		bud = HEADLESS;
-	} else {
-		z3fold_page_lock(zhdr);
-		bud = handle_to_buddy(handle);
-
-		switch (bud) {
-		case FIRST:
-			zhdr->first_chunks = 0;
-			break;
-		case MIDDLE:
-			zhdr->middle_chunks = 0;
-			zhdr->start_middle = 0;
-			break;
-		case LAST:
-			zhdr->last_chunks = 0;
-			break;
-		default:
-			pr_err("%s: unknown bud %d\n", __func__, bud);
-			WARN_ON(1);
-			z3fold_page_unlock(zhdr);
-			return;
+		/* if a headless page is under reclaim, just leave.
+		 * NB: we use test_and_set_bit for a reason: if the bit
+		 * has not been set before, we release this page
+		 * immediately so we don't care about its value any more.
+		 */
+		if (!test_and_set_bit(PAGE_CLAIMED, &page->private)) {
+			spin_lock(&pool->lock);
+			list_del(&page->lru);
+			spin_unlock(&pool->lock);
+			free_z3fold_page(page);
+			atomic64_dec(&pool->pages_nr);
 		}
+		return;
 	}
 
-	if (bud == HEADLESS) {
-		spin_lock(&pool->lock);
-		list_del(&page->lru);
-		spin_unlock(&pool->lock);
-		free_z3fold_page(page);
-		atomic64_dec(&pool->pages_nr);
+	/* Non-headless case */
+	z3fold_page_lock(zhdr);
+	bud = handle_to_buddy(handle);
+
+	switch (bud) {
+	case FIRST:
+		zhdr->first_chunks = 0;
+		break;
+	case MIDDLE:
+		zhdr->middle_chunks = 0;
+		break;
+	case LAST:
+		zhdr->last_chunks = 0;
+		break;
+	default:
+		pr_err("%s: unknown bud %d\n", __func__, bud);
+		WARN_ON(1);
+		z3fold_page_unlock(zhdr);
 		return;
 	}
 
@@ -758,7 +770,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 		atomic64_dec(&pool->pages_nr);
 		return;
 	}
-	if (test_bit(UNDER_RECLAIM, &page->private)) {
+	if (test_bit(PAGE_CLAIMED, &page->private)) {
 		z3fold_page_unlock(zhdr);
 		return;
 	}
@@ -836,20 +848,30 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 		}
 		list_for_each_prev(pos, &pool->lru) {
 			page = list_entry(pos, struct page, lru);
+
+			/* this bit could have been set by free, in which case
+			 * we pass over to the next page in the pool.
+			 */
+			if (test_and_set_bit(PAGE_CLAIMED, &page->private))
+				continue;
+
+			zhdr = page_address(page);
 			if (test_bit(PAGE_HEADLESS, &page->private))
-				/* candidate found */
 				break;
 
-			zhdr = page_address(page);
-			if (!z3fold_page_trylock(zhdr))
+			if (!z3fold_page_trylock(zhdr)) {
+				zhdr = NULL;
 				continue; /* can't evict at this point */
+			}
 			kref_get(&zhdr->refcount);
 			list_del_init(&zhdr->buddy);
 			zhdr->cpu = -1;
-			set_bit(UNDER_RECLAIM, &page->private);
 			break;
 		}
 
+		if (!zhdr)
+			break;
+
 		list_del_init(&page->lru);
 		spin_unlock(&pool->lock);
 
@@ -898,6 +920,7 @@ next:
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
 			if (ret == 0) {
 				free_z3fold_page(page);
+				atomic64_dec(&pool->pages_nr);
 				return 0;
 			}
 			spin_lock(&pool->lock);
@@ -905,7 +928,7 @@ next:
 			spin_unlock(&pool->lock);
 		} else {
 			z3fold_page_lock(zhdr);
-			clear_bit(UNDER_RECLAIM, &page->private);
+			clear_bit(PAGE_CLAIMED, &page->private);
 			if (kref_put(&zhdr->refcount,
 					release_z3fold_page_locked)) {
 				atomic64_dec(&pool->pages_nr);
@@ -964,7 +987,7 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
 		set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 		break;
 	case LAST:
-		addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
+		addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT);
 		break;
 	default:
 		pr_err("unknown buddy id %d\n", buddy);