diff mbox series

[117/158] mm/z3fold.c: add inter-page compaction

Message ID 20191201015611.fw2I5fblp%akpm@linux-foundation.org (mailing list archive)
State New, archived
Headers show
Series [001/158] scripts/spelling.txt: add more spellings to spelling.txt | expand

Commit Message

Andrew Morton Dec. 1, 2019, 1:56 a.m. UTC 
From: Vitaly Wool <vitaly.wool@konsulko.com>
Subject: mm/z3fold.c: add inter-page compaction

For each page scheduled for compaction (e.  g.  by z3fold_free()), try to
apply inter-page compaction before running the traditional/ existing
intra-page compaction.  That means, if the page has only one buddy, we
treat that buddy as a new object that we aim to place into an existing
z3fold page.  If such a page is found, that object is transferred and the
old page is freed completely.  The transferred object is named "foreign"
and treated slightly differently thereafter.

Namely, we increase "foreign handle" counter for the new page.  Pages with
non-zero "foreign handle" count become unmovable.  This patch implements
"foreign handle" detection when a handle is freed to decrement the foreign
handle counter accordingly, so a page may as well become movable again as
the time goes by.

As a result, we almost always have exactly 3 objects per page and
significantly better average compression ratio.

[cai@lca.pw: fix -Wunused-but-set-variable warnings]
  Link: http://lkml.kernel.org/r/1570542062-29144-1-git-send-email-cai@lca.pw
[vitalywool@gmail.com: avoid subtle race when freeing slots]
  Link: http://lkml.kernel.org/r/20191127152118.6314b99074b0626d4c5a8835@gmail.com
[vitalywool@gmail.com: compact objects more accurately]
  Link: http://lkml.kernel.org/r/20191127152216.6ad33745a21ba71c53606acb@gmail.com
[vitalywool@gmail.com: protect handle reads]
  Link: http://lkml.kernel.org/r/20191127152345.8059852f60947686674d726d@gmail.com
Link: http://lkml.kernel.org/r/20191006041457.24113-1-vitalywool@gmail.com
Signed-off-by: Vitaly Wool <vitaly.vul@sony.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/z3fold.c |  375 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 303 insertions(+), 72 deletions(-)
diff mbox series

Patch

--- a/mm/z3fold.c~z3fold-add-inter-page-compaction
+++ a/mm/z3fold.c
@@ -41,6 +41,7 @@ 
 #include <linux/workqueue.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/rwlock.h>
 #include <linux/zpool.h>
 #include <linux/magic.h>
 
@@ -90,6 +91,7 @@  struct z3fold_buddy_slots {
 	 */
 	unsigned long slot[BUDDY_MASK + 1];
 	unsigned long pool; /* back link + flags */
+	rwlock_t lock;
 };
 #define HANDLE_FLAG_MASK	(0x03)
 
@@ -124,6 +126,7 @@  struct z3fold_header {
 	unsigned short start_middle;
 	unsigned short first_num:2;
 	unsigned short mapped_count:2;
+	unsigned short foreign_handles:2;
 };
 
 /**
@@ -178,6 +181,19 @@  enum z3fold_page_flags {
 	PAGE_CLAIMED, /* by either reclaim or free */
 };
 
+/*
+ * handle flags, go under HANDLE_FLAG_MASK
+ */
+enum z3fold_handle_flags {
+	HANDLES_ORPHANED = 0,
+};
+
+/*
+ * Forward declarations
+ */
+static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool);
+static void compact_page_work(struct work_struct *w);
+
 /*****************
  * Helpers
 *****************/
@@ -191,8 +207,6 @@  static int size_to_chunks(size_t size)
 #define for_each_unbuddied_list(_iter, _begin) \
 	for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 
-static void compact_page_work(struct work_struct *w);
-
 static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
 							gfp_t gfp)
 {
@@ -204,6 +218,7 @@  static inline struct z3fold_buddy_slots
 	if (slots) {
 		memset(slots->slot, 0, sizeof(slots->slot));
 		slots->pool = (unsigned long)pool;
+		rwlock_init(&slots->lock);
 	}
 
 	return slots;
@@ -219,25 +234,110 @@  static inline struct z3fold_buddy_slots
 	return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
 }
 
+/* Lock a z3fold page */
+static inline void z3fold_page_lock(struct z3fold_header *zhdr)
+{
+	spin_lock(&zhdr->page_lock);
+}
+
+/* Try to lock a z3fold page */
+static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
+{
+	return spin_trylock(&zhdr->page_lock);
+}
+
+/* Unlock a z3fold page */
+static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
+{
+	spin_unlock(&zhdr->page_lock);
+}
+
+
+static inline struct z3fold_header *__get_z3fold_header(unsigned long handle,
+							bool lock)
+{
+	struct z3fold_buddy_slots *slots;
+	struct z3fold_header *zhdr;
+	int locked = 0;
+
+	if (!(handle & (1 << PAGE_HEADLESS))) {
+		slots = handle_to_slots(handle);
+		do {
+			unsigned long addr;
+
+			read_lock(&slots->lock);
+			addr = *(unsigned long *)handle;
+			zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
+			if (lock)
+				locked = z3fold_page_trylock(zhdr);
+			read_unlock(&slots->lock);
+			if (locked)
+				break;
+			cpu_relax();
+		} while (lock);
+	} else {
+		zhdr = (struct z3fold_header *)(handle & PAGE_MASK);
+	}
+
+	return zhdr;
+}
+
+/* Returns the z3fold page where a given handle is stored */
+static inline struct z3fold_header *handle_to_z3fold_header(unsigned long h)
+{
+	return __get_z3fold_header(h, false);
+}
+
+/* return locked z3fold page if it's not headless */
+static inline struct z3fold_header *get_z3fold_header(unsigned long h)
+{
+	return __get_z3fold_header(h, true);
+}
+
+static inline void put_z3fold_header(struct z3fold_header *zhdr)
+{
+	struct page *page = virt_to_page(zhdr);
+
+	if (!test_bit(PAGE_HEADLESS, &page->private))
+		z3fold_page_unlock(zhdr);
+}
+
 static inline void free_handle(unsigned long handle)
 {
 	struct z3fold_buddy_slots *slots;
+	struct z3fold_header *zhdr;
 	int i;
 	bool is_free;
 
 	if (handle & (1 << PAGE_HEADLESS))
 		return;
 
-	WARN_ON(*(unsigned long *)handle == 0);
-	*(unsigned long *)handle = 0;
+	if (WARN_ON(*(unsigned long *)handle == 0))
+		return;
+
+	zhdr = handle_to_z3fold_header(handle);
 	slots = handle_to_slots(handle);
+	write_lock(&slots->lock);
+	*(unsigned long *)handle = 0;
+	write_unlock(&slots->lock);
+	if (zhdr->slots == slots)
+		return; /* simple case, nothing else to do */
+
+	/* we are freeing a foreign handle if we are here */
+	zhdr->foreign_handles--;
 	is_free = true;
+	read_lock(&slots->lock);
+	if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
+		read_unlock(&slots->lock);
+		return;
+	}
 	for (i = 0; i <= BUDDY_MASK; i++) {
 		if (slots->slot[i]) {
 			is_free = false;
 			break;
 		}
 	}
+	read_unlock(&slots->lock);
 
 	if (is_free) {
 		struct z3fold_pool *pool = slots_to_pool(slots);
@@ -322,6 +422,7 @@  static struct z3fold_header *init_z3fold
 	zhdr->first_num = 0;
 	zhdr->start_middle = 0;
 	zhdr->cpu = -1;
+	zhdr->foreign_handles = 0;
 	zhdr->slots = slots;
 	zhdr->pool = pool;
 	INIT_LIST_HEAD(&zhdr->buddy);
@@ -341,24 +442,6 @@  static void free_z3fold_page(struct page
 	__free_page(page);
 }
 
-/* Lock a z3fold page */
-static inline void z3fold_page_lock(struct z3fold_header *zhdr)
-{
-	spin_lock(&zhdr->page_lock);
-}
-
-/* Try to lock a z3fold page */
-static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
-{
-	return spin_trylock(&zhdr->page_lock);
-}
-
-/* Unlock a z3fold page */
-static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
-{
-	spin_unlock(&zhdr->page_lock);
-}
-
 /* Helper function to build the index */
 static inline int __idx(struct z3fold_header *zhdr, enum buddy bud)
 {
@@ -389,7 +472,9 @@  static unsigned long __encode_handle(str
 	if (bud == LAST)
 		h |= (zhdr->last_chunks << BUDDY_SHIFT);
 
+	write_lock(&slots->lock);
 	slots->slot[idx] = h;
+	write_unlock(&slots->lock);
 	return (unsigned long)&slots->slot[idx];
 }
 
@@ -398,22 +483,15 @@  static unsigned long encode_handle(struc
 	return __encode_handle(zhdr, zhdr->slots, bud);
 }
 
-/* Returns the z3fold page where a given handle is stored */
-static inline struct z3fold_header *handle_to_z3fold_header(unsigned long h)
-{
-	unsigned long addr = h;
-
-	if (!(addr & (1 << PAGE_HEADLESS)))
-		addr = *(unsigned long *)h;
-
-	return (struct z3fold_header *)(addr & PAGE_MASK);
-}
-
 /* only for LAST bud, returns zero otherwise */
 static unsigned short handle_to_chunks(unsigned long handle)
 {
-	unsigned long addr = *(unsigned long *)handle;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
+	unsigned long addr;
 
+	read_lock(&slots->lock);
+	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 }
 
@@ -425,10 +503,13 @@  static unsigned short handle_to_chunks(u
 static enum buddy handle_to_buddy(unsigned long handle)
 {
 	struct z3fold_header *zhdr;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 	unsigned long addr;
 
+	read_lock(&slots->lock);
 	WARN_ON(handle & (1 << PAGE_HEADLESS));
 	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 	return (addr - zhdr->first_num) & BUDDY_MASK;
 }
@@ -442,6 +523,8 @@  static void __release_z3fold_page(struct
 {
 	struct page *page = virt_to_page(zhdr);
 	struct z3fold_pool *pool = zhdr_to_pool(zhdr);
+	bool is_free = true;
+	int i;
 
 	WARN_ON(!list_empty(&zhdr->buddy));
 	set_bit(PAGE_STALE, &page->private);
@@ -450,8 +533,25 @@  static void __release_z3fold_page(struct
 	if (!list_empty(&page->lru))
 		list_del_init(&page->lru);
 	spin_unlock(&pool->lock);
+
+	/* If there are no foreign handles, free the handles array */
+	read_lock(&zhdr->slots->lock);
+	for (i = 0; i <= BUDDY_MASK; i++) {
+		if (zhdr->slots->slot[i]) {
+			is_free = false;
+			break;
+		}
+	}
+	if (!is_free)
+		set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
+	read_unlock(&zhdr->slots->lock);
+
+	if (is_free)
+		kmem_cache_free(pool->c_handle, zhdr->slots);
+
 	if (locked)
 		z3fold_page_unlock(zhdr);
+
 	spin_lock(&pool->stale_lock);
 	list_add(&zhdr->buddy, &pool->stale);
 	queue_work(pool->release_wq, &pool->work);
@@ -479,6 +579,7 @@  static void release_z3fold_page_locked_l
 	struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
 					       refcount);
 	struct z3fold_pool *pool = zhdr_to_pool(zhdr);
+
 	spin_lock(&pool->lock);
 	list_del_init(&zhdr->buddy);
 	spin_unlock(&pool->lock);
@@ -559,6 +660,119 @@  static inline void *mchunk_memmove(struc
 		       zhdr->middle_chunks << CHUNK_SHIFT);
 }
 
+static inline bool buddy_single(struct z3fold_header *zhdr)
+{
+	return !((zhdr->first_chunks && zhdr->middle_chunks) ||
+			(zhdr->first_chunks && zhdr->last_chunks) ||
+			(zhdr->middle_chunks && zhdr->last_chunks));
+}
+
+static struct z3fold_header *compact_single_buddy(struct z3fold_header *zhdr)
+{
+	struct z3fold_pool *pool = zhdr_to_pool(zhdr);
+	void *p = zhdr;
+	unsigned long old_handle = 0;
+	size_t sz = 0;
+	struct z3fold_header *new_zhdr = NULL;
+	int first_idx = __idx(zhdr, FIRST);
+	int middle_idx = __idx(zhdr, MIDDLE);
+	int last_idx = __idx(zhdr, LAST);
+	unsigned short *moved_chunks = NULL;
+
+	/*
+	 * No need to protect slots here -- all the slots are "local" and
+	 * the page lock is already taken
+	 */
+	if (zhdr->first_chunks && zhdr->slots->slot[first_idx]) {
+		p += ZHDR_SIZE_ALIGNED;
+		sz = zhdr->first_chunks << CHUNK_SHIFT;
+		old_handle = (unsigned long)&zhdr->slots->slot[first_idx];
+		moved_chunks = &zhdr->first_chunks;
+	} else if (zhdr->middle_chunks && zhdr->slots->slot[middle_idx]) {
+		p += zhdr->start_middle << CHUNK_SHIFT;
+		sz = zhdr->middle_chunks << CHUNK_SHIFT;
+		old_handle = (unsigned long)&zhdr->slots->slot[middle_idx];
+		moved_chunks = &zhdr->middle_chunks;
+	} else if (zhdr->last_chunks && zhdr->slots->slot[last_idx]) {
+		p += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
+		sz = zhdr->last_chunks << CHUNK_SHIFT;
+		old_handle = (unsigned long)&zhdr->slots->slot[last_idx];
+		moved_chunks = &zhdr->last_chunks;
+	}
+
+	if (sz > 0) {
+		enum buddy new_bud = HEADLESS;
+		short chunks = size_to_chunks(sz);
+		void *q;
+
+		new_zhdr = __z3fold_alloc(pool, sz, false);
+		if (!new_zhdr)
+			return NULL;
+
+		if (WARN_ON(new_zhdr == zhdr))
+			goto out_fail;
+
+		if (new_zhdr->first_chunks == 0) {
+			if (new_zhdr->middle_chunks != 0 &&
+					chunks >= new_zhdr->start_middle) {
+				new_bud = LAST;
+			} else {
+				new_bud = FIRST;
+			}
+		} else if (new_zhdr->last_chunks == 0) {
+			new_bud = LAST;
+		} else if (new_zhdr->middle_chunks == 0) {
+			new_bud = MIDDLE;
+		}
+		q = new_zhdr;
+		switch (new_bud) {
+		case FIRST:
+			new_zhdr->first_chunks = chunks;
+			q += ZHDR_SIZE_ALIGNED;
+			break;
+		case MIDDLE:
+			new_zhdr->middle_chunks = chunks;
+			new_zhdr->start_middle =
+				new_zhdr->first_chunks + ZHDR_CHUNKS;
+			q += new_zhdr->start_middle << CHUNK_SHIFT;
+			break;
+		case LAST:
+			new_zhdr->last_chunks = chunks;
+			q += PAGE_SIZE - (new_zhdr->last_chunks << CHUNK_SHIFT);
+			break;
+		default:
+			goto out_fail;
+		}
+		new_zhdr->foreign_handles++;
+		memcpy(q, p, sz);
+		write_lock(&zhdr->slots->lock);
+		*(unsigned long *)old_handle = (unsigned long)new_zhdr +
+			__idx(new_zhdr, new_bud);
+		if (new_bud == LAST)
+			*(unsigned long *)old_handle |=
+					(new_zhdr->last_chunks << BUDDY_SHIFT);
+		write_unlock(&zhdr->slots->lock);
+		add_to_unbuddied(pool, new_zhdr);
+		z3fold_page_unlock(new_zhdr);
+
+		*moved_chunks = 0;
+	}
+
+	return new_zhdr;
+
+out_fail:
+	if (new_zhdr) {
+		if (kref_put(&new_zhdr->refcount, release_z3fold_page_locked))
+			atomic64_dec(&pool->pages_nr);
+		else {
+			add_to_unbuddied(pool, new_zhdr);
+			z3fold_page_unlock(new_zhdr);
+		}
+	}
+	return NULL;
+
+}
+
 #define BIG_CHUNK_GAP	3
 /* Has to be called with lock held */
 static int z3fold_compact_page(struct z3fold_header *zhdr)
@@ -638,6 +852,15 @@  static void do_compact_page(struct z3fol
 		return;
 	}
 
+	if (!zhdr->foreign_handles && buddy_single(zhdr) &&
+	    zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) {
+		if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
+			atomic64_dec(&pool->pages_nr);
+		else
+			z3fold_page_unlock(zhdr);
+		return;
+	}
+
 	z3fold_compact_page(zhdr);
 	add_to_unbuddied(pool, zhdr);
 	z3fold_page_unlock(zhdr);
@@ -690,7 +913,8 @@  lookup:
 		spin_unlock(&pool->lock);
 
 		page = virt_to_page(zhdr);
-		if (test_bit(NEEDS_COMPACTING, &page->private)) {
+		if (test_bit(NEEDS_COMPACTING, &page->private) ||
+		    test_bit(PAGE_CLAIMED, &page->private)) {
 			z3fold_page_unlock(zhdr);
 			zhdr = NULL;
 			put_cpu_ptr(pool->unbuddied);
@@ -734,7 +958,8 @@  lookup:
 			spin_unlock(&pool->lock);
 
 			page = virt_to_page(zhdr);
-			if (test_bit(NEEDS_COMPACTING, &page->private)) {
+			if (test_bit(NEEDS_COMPACTING, &page->private) ||
+			    test_bit(PAGE_CLAIMED, &page->private)) {
 				z3fold_page_unlock(zhdr);
 				zhdr = NULL;
 				if (can_sleep)
@@ -1000,7 +1225,7 @@  static void z3fold_free(struct z3fold_po
 	enum buddy bud;
 	bool page_claimed;
 
-	zhdr = handle_to_z3fold_header(handle);
+	zhdr = get_z3fold_header(handle);
 	page = virt_to_page(zhdr);
 	page_claimed = test_and_set_bit(PAGE_CLAIMED, &page->private);
 
@@ -1014,6 +1239,7 @@  static void z3fold_free(struct z3fold_po
 			spin_lock(&pool->lock);
 			list_del(&page->lru);
 			spin_unlock(&pool->lock);
+			put_z3fold_header(zhdr);
 			free_z3fold_page(page, true);
 			atomic64_dec(&pool->pages_nr);
 		}
@@ -1021,7 +1247,6 @@  static void z3fold_free(struct z3fold_po
 	}
 
 	/* Non-headless case */
-	z3fold_page_lock(zhdr);
 	bud = handle_to_buddy(handle);
 
 	switch (bud) {
@@ -1037,11 +1262,13 @@  static void z3fold_free(struct z3fold_po
 	default:
 		pr_err("%s: unknown bud %d\n", __func__, bud);
 		WARN_ON(1);
-		z3fold_page_unlock(zhdr);
+		put_z3fold_header(zhdr);
+		clear_bit(PAGE_CLAIMED, &page->private);
 		return;
 	}
 
-	free_handle(handle);
+	if (!page_claimed)
+		free_handle(handle);
 	if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 		atomic64_dec(&pool->pages_nr);
 		return;
@@ -1053,7 +1280,7 @@  static void z3fold_free(struct z3fold_po
 	}
 	if (unlikely(PageIsolated(page)) ||
 	    test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
-		z3fold_page_unlock(zhdr);
+		put_z3fold_header(zhdr);
 		clear_bit(PAGE_CLAIMED, &page->private);
 		return;
 	}
@@ -1063,14 +1290,14 @@  static void z3fold_free(struct z3fold_po
 		spin_unlock(&pool->lock);
 		zhdr->cpu = -1;
 		kref_get(&zhdr->refcount);
-		do_compact_page(zhdr, true);
 		clear_bit(PAGE_CLAIMED, &page->private);
+		do_compact_page(zhdr, true);
 		return;
 	}
 	kref_get(&zhdr->refcount);
-	queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
 	clear_bit(PAGE_CLAIMED, &page->private);
-	z3fold_page_unlock(zhdr);
+	queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
+	put_z3fold_header(zhdr);
 }
 
 /**
@@ -1111,11 +1338,10 @@  static void z3fold_free(struct z3fold_po
  */
 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 {
-	int i, ret = 0;
+	int i, ret = -1;
 	struct z3fold_header *zhdr = NULL;
 	struct page *page = NULL;
 	struct list_head *pos;
-	struct z3fold_buddy_slots slots;
 	unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
 
 	spin_lock(&pool->lock);
@@ -1153,6 +1379,12 @@  static int z3fold_reclaim_page(struct z3
 				zhdr = NULL;
 				continue; /* can't evict at this point */
 			}
+			if (zhdr->foreign_handles) {
+				clear_bit(PAGE_CLAIMED, &page->private);
+				z3fold_page_unlock(zhdr);
+				zhdr = NULL;
+				continue; /* can't evict such page */
+			}
 			kref_get(&zhdr->refcount);
 			list_del_init(&zhdr->buddy);
 			zhdr->cpu = -1;
@@ -1176,39 +1408,38 @@  static int z3fold_reclaim_page(struct z3
 			last_handle = 0;
 			middle_handle = 0;
 			if (zhdr->first_chunks)
-				first_handle = __encode_handle(zhdr, &slots,
-								FIRST);
+				first_handle = encode_handle(zhdr, FIRST);
 			if (zhdr->middle_chunks)
-				middle_handle = __encode_handle(zhdr, &slots,
-								MIDDLE);
+				middle_handle = encode_handle(zhdr, MIDDLE);
 			if (zhdr->last_chunks)
-				last_handle = __encode_handle(zhdr, &slots,
-								LAST);
+				last_handle = encode_handle(zhdr, LAST);
 			/*
 			 * it's safe to unlock here because we hold a
 			 * reference to this page
 			 */
 			z3fold_page_unlock(zhdr);
 		} else {
-			first_handle = __encode_handle(zhdr, &slots, HEADLESS);
+			first_handle = encode_handle(zhdr, HEADLESS);
 			last_handle = middle_handle = 0;
 		}
-
 		/* Issue the eviction callback(s) */
 		if (middle_handle) {
 			ret = pool->ops->evict(pool, middle_handle);
 			if (ret)
 				goto next;
+			free_handle(middle_handle);
 		}
 		if (first_handle) {
 			ret = pool->ops->evict(pool, first_handle);
 			if (ret)
 				goto next;
+			free_handle(first_handle);
 		}
 		if (last_handle) {
 			ret = pool->ops->evict(pool, last_handle);
 			if (ret)
 				goto next;
+			free_handle(last_handle);
 		}
 next:
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
@@ -1264,14 +1495,13 @@  static void *z3fold_map(struct z3fold_po
 	void *addr;
 	enum buddy buddy;
 
-	zhdr = handle_to_z3fold_header(handle);
+	zhdr = get_z3fold_header(handle);
 	addr = zhdr;
 	page = virt_to_page(zhdr);
 
 	if (test_bit(PAGE_HEADLESS, &page->private))
 		goto out;
 
-	z3fold_page_lock(zhdr);
 	buddy = handle_to_buddy(handle);
 	switch (buddy) {
 	case FIRST:
@@ -1293,8 +1523,8 @@  static void *z3fold_map(struct z3fold_po
 
 	if (addr)
 		zhdr->mapped_count++;
-	z3fold_page_unlock(zhdr);
 out:
+	put_z3fold_header(zhdr);
 	return addr;
 }
 
@@ -1309,18 +1539,17 @@  static void z3fold_unmap(struct z3fold_p
 	struct page *page;
 	enum buddy buddy;
 
-	zhdr = handle_to_z3fold_header(handle);
+	zhdr = get_z3fold_header(handle);
 	page = virt_to_page(zhdr);
 
 	if (test_bit(PAGE_HEADLESS, &page->private))
 		return;
 
-	z3fold_page_lock(zhdr);
 	buddy = handle_to_buddy(handle);
 	if (buddy == MIDDLE)
 		clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 	zhdr->mapped_count--;
-	z3fold_page_unlock(zhdr);
+	put_z3fold_header(zhdr);
 }
 
 /**
@@ -1352,19 +1581,21 @@  static bool z3fold_page_isolate(struct p
 	    test_bit(PAGE_STALE, &page->private))
 		goto out;
 
+	if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0)
+		goto out;
+
 	pool = zhdr_to_pool(zhdr);
+	spin_lock(&pool->lock);
+	if (!list_empty(&zhdr->buddy))
+		list_del_init(&zhdr->buddy);
+	if (!list_empty(&page->lru))
+		list_del_init(&page->lru);
+	spin_unlock(&pool->lock);
+
+	kref_get(&zhdr->refcount);
+	z3fold_page_unlock(zhdr);
+	return true;
 
-	if (zhdr->mapped_count == 0) {
-		kref_get(&zhdr->refcount);
-		if (!list_empty(&zhdr->buddy))
-			list_del_init(&zhdr->buddy);
-		spin_lock(&pool->lock);
-		if (!list_empty(&page->lru))
-			list_del(&page->lru);
-		spin_unlock(&pool->lock);
-		z3fold_page_unlock(zhdr);
-		return true;
-	}
 out:
 	z3fold_page_unlock(zhdr);
 	return false;
@@ -1387,7 +1618,7 @@  static int z3fold_page_migrate(struct ad
 	if (!z3fold_page_trylock(zhdr)) {
 		return -EAGAIN;
 	}
-	if (zhdr->mapped_count != 0) {
+	if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
 		z3fold_page_unlock(zhdr);
 		return -EBUSY;
 	}