The quilt patch titled
Subject: mm/zswap: change zswap_pool kref to percpu_ref
has been removed from the -mm tree. Its filename was
mm-zswap-change-zswap_pool-kref-to-percpu_ref.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Subject: mm/zswap: change zswap_pool kref to percpu_ref
Date: Fri, 16 Feb 2024 08:55:05 +0000
All zswap entries will take a reference of zswap_pool when zswap_store(),
and drop it when free. Change it to use the percpu_ref is better for
scalability performance.
Although percpu_ref use a bit more memory which should be ok for our use
case, since we almost have only one zswap_pool to be using. The
performance gain is for zswap_store/load hotpath.
Testing kernel build (32 threads) in tmpfs with memory.max=2GB. (zswap
shrinker and writeback enabled with one 50GB swapfile, on a 128 CPUs
x86-64 machine, below is the average of 5 runs)
mm-unstable zswap-global-lru
real 63.20 63.12
user 1061.75 1062.95
sys 268.74 264.44
[chengming.zhou@xxxxxxxxx: fix zswap_pools_lock usages after changing to percpu_ref]
Link: https://lkml.kernel.org/r/20240228154954.3028626-1-chengming.zhou@xxxxxxxxx
Link: https://lkml.kernel.org/r/20240210-zswap-global-lru-v3-2-200495333595@xxxxxxxxxxxxx
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 48 +++++++++++++++++++++++++++++++++---------------
1 file changed, 33 insertions(+), 15 deletions(-)
--- a/mm/zswap.c~mm-zswap-change-zswap_pool-kref-to-percpu_ref
+++ a/mm/zswap.c
@@ -173,7 +173,7 @@ struct crypto_acomp_ctx {
struct zswap_pool {
struct zpool *zpools[ZSWAP_NR_ZPOOLS];
struct crypto_acomp_ctx __percpu *acomp_ctx;
- struct kref kref;
+ struct percpu_ref ref;
struct list_head list;
struct work_struct release_work;
struct hlist_node node;
@@ -305,6 +305,7 @@ static void zswap_update_total_size(void
/*********************************
* pool functions
**********************************/
+static void __zswap_pool_empty(struct percpu_ref *ref);
static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
{
@@ -358,13 +359,18 @@ static struct zswap_pool *zswap_pool_cre
/* being the current pool takes 1 ref; this func expects the
* caller to always add the new pool as the current pool
*/
- kref_init(&pool->kref);
+ ret = percpu_ref_init(&pool->ref, __zswap_pool_empty,
+ PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
+ if (ret)
+ goto ref_fail;
INIT_LIST_HEAD(&pool->list);
zswap_pool_debug("created", pool);
return pool;
+ref_fail:
+ cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
error:
if (pool->acomp_ctx)
free_percpu(pool->acomp_ctx);
@@ -437,8 +443,9 @@ static void __zswap_pool_release(struct
synchronize_rcu();
- /* nobody should have been able to get a kref... */
- WARN_ON(kref_get_unless_zero(&pool->kref));
+ /* nobody should have been able to get a ref... */
+ WARN_ON(!percpu_ref_is_zero(&pool->ref));
+ percpu_ref_exit(&pool->ref);
/* pool is now off zswap_pools list and has no references. */
zswap_pool_destroy(pool);
@@ -446,13 +453,13 @@ static void __zswap_pool_release(struct
static struct zswap_pool *zswap_pool_current(void);
-static void __zswap_pool_empty(struct kref *kref)
+static void __zswap_pool_empty(struct percpu_ref *ref)
{
struct zswap_pool *pool;
- pool = container_of(kref, typeof(*pool), kref);
+ pool = container_of(ref, typeof(*pool), ref);
- spin_lock(&zswap_pools_lock);
+ spin_lock_bh(&zswap_pools_lock);
WARN_ON(pool == zswap_pool_current());
@@ -461,7 +468,7 @@ static void __zswap_pool_empty(struct kr
INIT_WORK(&pool->release_work, __zswap_pool_release);
schedule_work(&pool->release_work);
- spin_unlock(&zswap_pools_lock);
+ spin_unlock_bh(&zswap_pools_lock);
}
static int __must_check zswap_pool_get(struct zswap_pool *pool)
@@ -469,12 +476,12 @@ static int __must_check zswap_pool_get(s
if (!pool)
return 0;
- return kref_get_unless_zero(&pool->kref);
+ return percpu_ref_tryget(&pool->ref);
}
static void zswap_pool_put(struct zswap_pool *pool)
{
- kref_put(&pool->kref, __zswap_pool_empty);
+ percpu_ref_put(&pool->ref);
}
static struct zswap_pool *__zswap_pool_current(void)
@@ -591,7 +598,7 @@ static int __zswap_param_set(const char
return -EINVAL;
}
- spin_lock(&zswap_pools_lock);
+ spin_lock_bh(&zswap_pools_lock);
pool = zswap_pool_find_get(type, compressor);
if (pool) {
@@ -600,17 +607,28 @@ static int __zswap_param_set(const char
list_del_rcu(&pool->list);
}
- spin_unlock(&zswap_pools_lock);
+ spin_unlock_bh(&zswap_pools_lock);
if (!pool)
pool = zswap_pool_create(type, compressor);
+ else {
+ /*
+ * Restore the initial ref dropped by percpu_ref_kill()
+ * when the pool was decommissioned and switch it again
+ * to percpu mode.
+ */
+ percpu_ref_resurrect(&pool->ref);
+
+ /* Drop the ref from zswap_pool_find_get(). */
+ zswap_pool_put(pool);
+ }
if (pool)
ret = param_set_charp(s, kp);
else
ret = -EINVAL;
- spin_lock(&zswap_pools_lock);
+ spin_lock_bh(&zswap_pools_lock);
if (!ret) {
put_pool = zswap_pool_current();
@@ -625,7 +643,7 @@ static int __zswap_param_set(const char
put_pool = pool;
}
- spin_unlock(&zswap_pools_lock);
+ spin_unlock_bh(&zswap_pools_lock);
if (!zswap_has_pool && !pool) {
/* if initial pool creation failed, and this pool creation also
@@ -642,7 +660,7 @@ static int __zswap_param_set(const char
* or the new pool we failed to add
*/
if (put_pool)
- zswap_pool_put(put_pool);
+ percpu_ref_kill(&put_pool->ref);
return ret;
}
_
Patches currently in -mm which might be from zhouchengming@xxxxxxxxxxxxx are
