This patch converts pages_nr per-pool counter to atomic64_t.
It also introduces a new counter, unbuddied_nr, which is also
atomic64_t, to track the number of unbuddied (shrinkable) pages,
as a step to prepare for z3fold shrinker implementation.

Signed-off-by: Vitaly Wool <vitalyw...@gmail.com>
---
 mm/z3fold.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 8f9e89c..5197d7b 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -69,6 +69,7 @@ struct z3fold_ops {
  * @lru:       list tracking the z3fold pages in LRU order by most recently
  *             added buddy.
  * @pages_nr:  number of z3fold pages in the pool.
+ * @unbuddied_nr:      number of unbuddied z3fold pages in the pool.
  * @ops:       pointer to a structure of user defined operations specified at
  *             pool creation time.
  *
@@ -80,7 +81,8 @@ struct z3fold_pool {
        struct list_head unbuddied[NCHUNKS];
        struct list_head buddied;
        struct list_head lru;
-       u64 pages_nr;
+       atomic64_t pages_nr;
+       atomic64_t unbuddied_nr;
        const struct z3fold_ops *ops;
        struct zpool *zpool;
        const struct zpool_ops *zpool_ops;
@@ -234,7 +236,8 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
                INIT_LIST_HEAD(&pool->unbuddied[i]);
        INIT_LIST_HEAD(&pool->buddied);
        INIT_LIST_HEAD(&pool->lru);
-       pool->pages_nr = 0;
+       atomic64_set(&pool->pages_nr, 0);
+       atomic64_set(&pool->unbuddied_nr, 0);
        pool->ops = ops;
        return pool;
 }
@@ -334,6 +337,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t 
size, gfp_t gfp,
                                        continue;
                                }
                                list_del(&zhdr->buddy);
+                               atomic64_dec(&pool->unbuddied_nr);
                                goto found;
                        }
                }
@@ -346,7 +350,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t 
size, gfp_t gfp,
        if (!page)
                return -ENOMEM;
        spin_lock(&pool->lock);
-       pool->pages_nr++;
+       atomic64_inc(&pool->pages_nr);
        zhdr = init_z3fold_page(page);
 
        if (bud == HEADLESS) {
@@ -369,6 +373,7 @@ found:
                /* Add to unbuddied list */
                freechunks = num_free_chunks(zhdr);
                list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+               atomic64_inc(&pool->unbuddied_nr);
        } else {
                /* Add to buddied list */
                list_add(&zhdr->buddy, &pool->buddied);
@@ -412,6 +417,11 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned 
long handle)
                /* HEADLESS page stored */
                bud = HEADLESS;
        } else {
+               if (zhdr->first_chunks == 0 ||
+                   zhdr->middle_chunks == 0 ||
+                   zhdr->last_chunks == 0)
+                       atomic64_dec(&pool->unbuddied_nr);
+
                bud = handle_to_buddy(handle);
 
                switch (bud) {
@@ -429,6 +439,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned 
long handle)
                        pr_err("%s: unknown bud %d\n", __func__, bud);
                        WARN_ON(1);
                        spin_unlock(&pool->lock);
+                       atomic64_inc(&pool->unbuddied_nr);
                        return;
                }
        }
@@ -451,12 +462,13 @@ static void z3fold_free(struct z3fold_pool *pool, 
unsigned long handle)
                list_del(&page->lru);
                clear_bit(PAGE_HEADLESS, &page->private);
                free_z3fold_page(zhdr);
-               pool->pages_nr--;
+               atomic64_dec(&pool->pages_nr);
        } else {
                z3fold_compact_page(zhdr);
                /* Add to the unbuddied list */
                freechunks = num_free_chunks(zhdr);
                list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+               atomic64_inc(&pool->unbuddied_nr);
        }
 
        spin_unlock(&pool->lock);
@@ -520,6 +532,11 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, 
unsigned int retries)
                zhdr = page_address(page);
                if (!test_bit(PAGE_HEADLESS, &page->private)) {
                        list_del(&zhdr->buddy);
+                       if (zhdr->first_chunks == 0 ||
+                           zhdr->middle_chunks == 0 ||
+                           zhdr->last_chunks == 0)
+                               atomic64_dec(&pool->unbuddied_nr);
+
                        /*
                         * We need encode the handles before unlocking, since
                         * we can race with free that will set
@@ -569,7 +586,7 @@ next:
                         */
                        clear_bit(PAGE_HEADLESS, &page->private);
                        free_z3fold_page(zhdr);
-                       pool->pages_nr--;
+                       atomic64_dec(&pool->pages_nr);
                        spin_unlock(&pool->lock);
                        return 0;
                }  else if (!test_bit(PAGE_HEADLESS, &page->private)) {
@@ -584,6 +601,7 @@ next:
                                freechunks = num_free_chunks(zhdr);
                                list_add(&zhdr->buddy,
                                         &pool->unbuddied[freechunks]);
+                               atomic64_inc(&pool->unbuddied_nr);
                        }
                }
 
@@ -672,12 +690,11 @@ static void z3fold_unmap(struct z3fold_pool *pool, 
unsigned long handle)
  * z3fold_get_pool_size() - gets the z3fold pool size in pages
  * @pool:      pool whose size is being queried
  *
- * Returns: size in pages of the given pool.  The pool lock need not be
- * taken to access pages_nr.
+ * Returns: size in pages of the given pool.
  */
 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
 {
-       return pool->pages_nr;
+       return atomic64_read(&pool->pages_nr);
 }
 
 /*****************
-- 
2.4.2

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