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);