Re: [PATCH] mm, slab: Extend slab/shrink to shrink all the memcg caches

peter enderborg
2019-07-22T12:56:58Z

On 7/2/19 8:37 PM, Waiman Long wrote:
> Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink
> file to shrink the slab by flushing all the per-cpu slabs and free
> slabs in partial lists. This applies only to the root caches, though.
>
> Extends this capability by shrinking all the child memcg caches and
> the root cache when a value of '2' is written to the shrink sysfs file.
>
> On a 4-socket 112-core 224-thread x86-64 system after a parallel kernel
> build, the the amount of memory occupied by slabs before shrinking
> slabs were:
>
> # grep task_struct /proc/slabinfo
> task_struct 7114 7296 7744 4 8 : tunables 0 0
> 0 : slabdata 1824 1824 0
> # grep "^S[lRU]" /proc/meminfo
> Slab: 1310444 kB
> SReclaimable: 377604 kB
> SUnreclaim: 932840 kB
>
> After shrinking slabs:
>
> # grep "^S[lRU]" /proc/meminfo
> Slab: 695652 kB
> SReclaimable: 322796 kB
> SUnreclaim: 372856 kB
> # grep task_struct /proc/slabinfo
> task_struct 2262 2572 7744 4 8 : tunables 0 0
> 0 : slabdata 643 643 0

What is the time between this measurement points? Should not the shrinked memory show up as reclaimable?

> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> Documentation/ABI/testing/sysfs-kernel-slab | 10 +++--
> mm/slab.h | 1 +
> mm/slab_common.c | 43 +++++++++++++++++++++
> mm/slub.c | 2 +
> 4 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab
> index 29601d93a1c2..2a3d0fc4b4ac 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-slab
> +++ b/Documentation/ABI/testing/sysfs-kernel-slab
> @@ -429,10 +429,12 @@ KernelVersion: 2.6.22
> Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
> Christoph Lameter <cl@linux-foundation.org>
> Description:
> - The shrink file is written when memory should be reclaimed from
> - a cache. Empty partial slabs are freed and the partial list is
> - sorted so the slabs with the fewest available objects are used
> - first.
> + A value of '1' is written to the shrink file when memory should
> + be reclaimed from a cache. Empty partial slabs are freed and
> + the partial list is sorted so the slabs with the fewest
> + available objects are used first. When a value of '2' is
> + written, all the corresponding child memory cgroup caches
> + should be shrunk as well. All other values are invalid.
>
> What: /sys/kernel/slab/cache/slab_size
> Date: May 2007
> diff --git a/mm/slab.h b/mm/slab.h
> index 3b22931bb557..a16b2c7ff4dd 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -174,6 +174,7 @@ int __kmem_cache_shrink(struct kmem_cache *);
> void __kmemcg_cache_deactivate(struct kmem_cache *s);
> void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s);
> void slab_kmem_cache_release(struct kmem_cache *);
> +int kmem_cache_shrink_all(struct kmem_cache *s);
>
> struct seq_file;
> struct file;
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 464faaa9fd81..493697ba1da5 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -981,6 +981,49 @@ int kmem_cache_shrink(struct kmem_cache *cachep)
> }
> EXPORT_SYMBOL(kmem_cache_shrink);
>
> +/**
> + * kmem_cache_shrink_all - shrink a cache and all its memcg children
> + * @s: The root cache to shrink.
> + *
> + * Return: 0 if successful, -EINVAL if not a root cache
> + */
> +int kmem_cache_shrink_all(struct kmem_cache *s)
> +{
> + struct kmem_cache *c;
> +
> + if (!IS_ENABLED(CONFIG_MEMCG_KMEM)) {
> + kmem_cache_shrink(s);
> + return 0;
> + }
> + if (!is_root_cache(s))
> + return -EINVAL;
> +
> + /*
> + * The caller should have a reference to the root cache and so
> + * we don't need to take the slab_mutex. We have to take the
> + * slab_mutex, however, to iterate the memcg caches.
> + */
> + get_online_cpus();
> + get_online_mems();
> + kasan_cache_shrink(s);
> + __kmem_cache_shrink(s);
> +
> + mutex_lock(&slab_mutex);
> + for_each_memcg_cache(c, s) {
> + /*
> + * Don't need to shrink deactivated memcg caches.
> + */
> + if (s->flags & SLAB_DEACTIVATED)
> + continue;
> + kasan_cache_shrink(c);
> + __kmem_cache_shrink(c);
> + }
> + mutex_unlock(&slab_mutex);
> + put_online_mems();
> + put_online_cpus();
> + return 0;
> +}
> +
> bool slab_is_available(void)
> {
> return slab_state >= UP;
> diff --git a/mm/slub.c b/mm/slub.c
> index a384228ff6d3..5d7b0004c51f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5298,6 +5298,8 @@ static ssize_t shrink_store(struct kmem_cache *s,
> {
> if (buf[0] == '1')
> kmem_cache_shrink(s);
> + else if (buf[0] == '2')
> + kmem_cache_shrink_all(s);
> else
> return -EINVAL;
> return length;