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Subject[PATCH v5 1/3] z3fold: make counters atomic
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 <vitalywool@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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