| Message ID | 20240210-zswap-global-lru-v1-2-853473d7b0da@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/zswap: optimize for dynamic zswap_pools | expand |
On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou <zhouchengming@bytedance.com> wrote: > > 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. > > Testing kernel build in tmpfs with memory.max=2GB > (zswap shrinker and writeback enabled with one 50GB swapfile). > > mm-unstable zswap-global-lru > real 63.20 63.12 > user 1061.75 1062.95 > sys 268.74 264.44 > > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > --- > mm/zswap.c | 30 +++++++++++++++++++++--------- > 1 file changed, 21 insertions(+), 9 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 7668db8c10e3..afb31904fb08 100644 > --- a/mm/zswap.c > +++ b/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; > @@ -303,6 +303,7 @@ 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) > { > @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > /* 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); > @@ -435,8 +441,8 @@ static void __zswap_pool_release(struct work_struct *work) > > synchronize_rcu(); > > - /* nobody should have been able to get a kref... */ > - WARN_ON(kref_get_unless_zero(&pool->kref)); Do we no longer care about this WARN? IIUC, this is to catch someone still holding a reference to the pool at release time, which sounds like a bug. I think we can simulate the similar behavior with: WARN_ON(percpu_ref_tryget(&pool->ref)) no? percpu_ref_tryget() should fail when the refcnt goes back down to 0. Then we can do percpu_ref_exit() as well. > + /* nobody should have been able to get a ref... */ > + percpu_ref_exit(&pool->ref); > > /* pool is now off zswap_pools list and has no references. */ > zswap_pool_destroy(pool); > @@ -444,11 +450,11 @@ static void __zswap_pool_release(struct work_struct *work) > > 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); > > @@ -467,12 +473,12 @@ static int __must_check zswap_pool_get(struct zswap_pool *pool) > 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) > @@ -602,6 +608,12 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, > > if (!pool) > pool = zswap_pool_create(type, compressor); > + else { > + /* Resurrect percpu_ref 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); > @@ -640,7 +652,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, > * or the new pool we failed to add > */ > if (put_pool) > - zswap_pool_put(put_pool); > + percpu_ref_kill(&put_pool->ref); > > return ret; > } > > -- > b4 0.10.1 The rest of the code looks solid to me FWIW. Number seems to indicate this is a good idea as well.
On 2024/2/12 05:21, Nhat Pham wrote: > On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou > <zhouchengming@bytedance.com> wrote: >> >> 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. >> >> Testing kernel build in tmpfs with memory.max=2GB >> (zswap shrinker and writeback enabled with one 50GB swapfile). >> >> mm-unstable zswap-global-lru >> real 63.20 63.12 >> user 1061.75 1062.95 >> sys 268.74 264.44 >> >> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> >> --- >> mm/zswap.c | 30 +++++++++++++++++++++--------- >> 1 file changed, 21 insertions(+), 9 deletions(-) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> index 7668db8c10e3..afb31904fb08 100644 >> --- a/mm/zswap.c >> +++ b/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; >> @@ -303,6 +303,7 @@ 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) >> { >> @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) >> /* 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); >> @@ -435,8 +441,8 @@ static void __zswap_pool_release(struct work_struct *work) >> >> synchronize_rcu(); >> >> - /* nobody should have been able to get a kref... */ >> - WARN_ON(kref_get_unless_zero(&pool->kref)); > > Do we no longer care about this WARN? IIUC, this is to catch someone > still holding a reference to the pool at release time, which sounds > like a bug. I think we can simulate the similar behavior with: Ok, I thought it has already been put to 0 when we're here, so any tryget will fail. But keeping this WARN_ON() is also fine to me, will keep it. Thanks. > > WARN_ON(percpu_ref_tryget(&pool->ref)) > > no? percpu_ref_tryget() should fail when the refcnt goes back down to > 0. Then we can do percpu_ref_exit() as well. > >> + /* nobody should have been able to get a ref... */ >> + percpu_ref_exit(&pool->ref); >> >> /* pool is now off zswap_pools list and has no references. */ >> zswap_pool_destroy(pool); >> @@ -444,11 +450,11 @@ static void __zswap_pool_release(struct work_struct *work) >> >> 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); >> >> @@ -467,12 +473,12 @@ static int __must_check zswap_pool_get(struct zswap_pool *pool) >> 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) >> @@ -602,6 +608,12 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, >> >> if (!pool) >> pool = zswap_pool_create(type, compressor); >> + else { >> + /* Resurrect percpu_ref 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); >> @@ -640,7 +652,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, >> * or the new pool we failed to add >> */ >> if (put_pool) >> - zswap_pool_put(put_pool); >> + percpu_ref_kill(&put_pool->ref); >> >> return ret; >> } >> >> -- >> b4 0.10.1 > > The rest of the code looks solid to me FWIW. Number seems to indicate > this is a good idea as well.
On Mon, Feb 12, 2024 at 5:29 AM Chengming Zhou <zhouchengming@bytedance.com> wrote: > > On 2024/2/12 05:21, Nhat Pham wrote: > > On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou > > <zhouchengming@bytedance.com> wrote: > >> > >> 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. > >> > >> Testing kernel build in tmpfs with memory.max=2GB > >> (zswap shrinker and writeback enabled with one 50GB swapfile). > >> > >> mm-unstable zswap-global-lru > >> real 63.20 63.12 > >> user 1061.75 1062.95 > >> sys 268.74 264.44 > >> > >> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > >> --- > >> mm/zswap.c | 30 +++++++++++++++++++++--------- > >> 1 file changed, 21 insertions(+), 9 deletions(-) > >> > >> diff --git a/mm/zswap.c b/mm/zswap.c > >> index 7668db8c10e3..afb31904fb08 100644 > >> --- a/mm/zswap.c > >> +++ b/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; > >> @@ -303,6 +303,7 @@ 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) > >> { > >> @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) > >> /* 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); > >> @@ -435,8 +441,8 @@ static void __zswap_pool_release(struct work_struct *work) > >> > >> synchronize_rcu(); > >> > >> - /* nobody should have been able to get a kref... */ > >> - WARN_ON(kref_get_unless_zero(&pool->kref)); > > > > Do we no longer care about this WARN? IIUC, this is to catch someone > > still holding a reference to the pool at release time, which sounds > > like a bug. I think we can simulate the similar behavior with: > > Ok, I thought it has already been put to 0 when we're here, so any tryget > will fail. But keeping this WARN_ON() is also fine to me, will keep it. Yup - it should fail, if the code is not buggy. But that's a pretty big if :) Jokes aside, we can remove it if folks think the benefit is not worth the cost/overhead. However, I'm a bit hesitant to remove checks in zswap, especially given how buggy it has been (some of which are refcnt bugs as well, IIRC).
On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou <zhouchengming@bytedance.com> wrote: > > 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. > > Testing kernel build in tmpfs with memory.max=2GB > (zswap shrinker and writeback enabled with one 50GB swapfile). > > mm-unstable zswap-global-lru > real 63.20 63.12 > user 1061.75 1062.95 > sys 268.74 264.44 Are these numbers from a single run or the average of multiple runs? It just seems that the improvement is small, and percpu refcnt is slightly less intuitive (and uses a bit more memory), so let's make sure there is a real performance gain first. It would also be useful to mention how many threads/CPUs are being used here.
On 2024/2/13 02:53, Nhat Pham wrote: > On Mon, Feb 12, 2024 at 5:29 AM Chengming Zhou > <zhouchengming@bytedance.com> wrote: >> >> On 2024/2/12 05:21, Nhat Pham wrote: >>> On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou >>> <zhouchengming@bytedance.com> wrote: >>>> >>>> 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. >>>> >>>> Testing kernel build in tmpfs with memory.max=2GB >>>> (zswap shrinker and writeback enabled with one 50GB swapfile). >>>> >>>> mm-unstable zswap-global-lru >>>> real 63.20 63.12 >>>> user 1061.75 1062.95 >>>> sys 268.74 264.44 >>>> >>>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> >>>> --- >>>> mm/zswap.c | 30 +++++++++++++++++++++--------- >>>> 1 file changed, 21 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/mm/zswap.c b/mm/zswap.c >>>> index 7668db8c10e3..afb31904fb08 100644 >>>> --- a/mm/zswap.c >>>> +++ b/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; >>>> @@ -303,6 +303,7 @@ 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) >>>> { >>>> @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) >>>> /* 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); >>>> @@ -435,8 +441,8 @@ static void __zswap_pool_release(struct work_struct *work) >>>> >>>> synchronize_rcu(); >>>> >>>> - /* nobody should have been able to get a kref... */ >>>> - WARN_ON(kref_get_unless_zero(&pool->kref)); >>> >>> Do we no longer care about this WARN? IIUC, this is to catch someone >>> still holding a reference to the pool at release time, which sounds >>> like a bug. I think we can simulate the similar behavior with: >> >> Ok, I thought it has already been put to 0 when we're here, so any tryget >> will fail. But keeping this WARN_ON() is also fine to me, will keep it. > > Yup - it should fail, if the code is not buggy. But that's a pretty big if :) > > Jokes aside, we can remove it if folks think the benefit is not worth > the cost/overhead. However, I'm a bit hesitant to remove checks in > zswap, especially given how buggy it has been (some of which are > refcnt bugs as well, IIRC). Yes, agree. It looks clearer to keep it, which should be no cost at all. Thanks!
On 2024/2/13 06:42, Yosry Ahmed wrote: > On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou > <zhouchengming@bytedance.com> wrote: >> >> 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. >> >> Testing kernel build in tmpfs with memory.max=2GB >> (zswap shrinker and writeback enabled with one 50GB swapfile). >> >> mm-unstable zswap-global-lru >> real 63.20 63.12 >> user 1061.75 1062.95 >> sys 268.74 264.44 > > Are these numbers from a single run or the average of multiple runs? The average of 5 runs. And I just checked/compared each run result, the improvement is stable. So yes, it should be a real performance gain. > It just seems that the improvement is small, and percpu refcnt is > slightly less intuitive (and uses a bit more memory), so let's make > sure there is a real performance gain first. Right, 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. > > It would also be useful to mention how many threads/CPUs are being used here. My bad, the testing uses 32 threads on a 128 CPUs x86-64 machine. Thanks.
On Tue, Feb 13, 2024 at 10:31:16PM +0800, Chengming Zhou wrote: > On 2024/2/13 06:42, Yosry Ahmed wrote: > > On Sun, Feb 11, 2024 at 5:58 AM Chengming Zhou > > <zhouchengming@bytedance.com> wrote: > >> > >> 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. > >> > >> Testing kernel build in tmpfs with memory.max=2GB > >> (zswap shrinker and writeback enabled with one 50GB swapfile). > >> > >> mm-unstable zswap-global-lru > >> real 63.20 63.12 > >> user 1061.75 1062.95 > >> sys 268.74 264.44 > > > > Are these numbers from a single run or the average of multiple runs? > > The average of 5 runs. And I just checked/compared each run result, > the improvement is stable. So yes, it should be a real performance gain. > > > It just seems that the improvement is small, and percpu refcnt is > > slightly less intuitive (and uses a bit more memory), so let's make > > sure there is a real performance gain first. > > Right, 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. > > > > > It would also be useful to mention how many threads/CPUs are being used here. > > My bad, the testing uses 32 threads on a 128 CPUs x86-64 machine. Thanks for the clarification. Please include such details in the commit message.
diff --git a/mm/zswap.c b/mm/zswap.c index 7668db8c10e3..afb31904fb08 100644 --- a/mm/zswap.c +++ b/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; @@ -303,6 +303,7 @@ 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) { @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) /* 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); @@ -435,8 +441,8 @@ static void __zswap_pool_release(struct work_struct *work) 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... */ + percpu_ref_exit(&pool->ref); /* pool is now off zswap_pools list and has no references. */ zswap_pool_destroy(pool); @@ -444,11 +450,11 @@ static void __zswap_pool_release(struct work_struct *work) 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); @@ -467,12 +473,12 @@ static int __must_check zswap_pool_get(struct zswap_pool *pool) 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) @@ -602,6 +608,12 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, if (!pool) pool = zswap_pool_create(type, compressor); + else { + /* Resurrect percpu_ref 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); @@ -640,7 +652,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, * or the new pool we failed to add */ if (put_pool) - zswap_pool_put(put_pool); + percpu_ref_kill(&put_pool->ref); return ret; }
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. Testing kernel build in tmpfs with memory.max=2GB (zswap shrinker and writeback enabled with one 50GB swapfile). mm-unstable zswap-global-lru real 63.20 63.12 user 1061.75 1062.95 sys 268.74 264.44 Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> --- mm/zswap.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-)