Alex, Vlasimil, Michal, thanks for your responses!
On Fri, Dec 02, 2016 at 10:19:33AM +0100, Michal Hocko wrote:
> Thanks for CCing me Vlastimil
>
> On Fri 02-12-16 09:44:23, Vlastimil Babka wrote:
> > On 12/01/2016 02:16 AM, Anatoly Stepanov wrote:
> > > As memcg array size can be up to:
> > > sizeof(struct memcg_cache_array) + kmemcg_id * sizeof(void *);
> > >
> > > where kmemcg_id can be up to MEMCG_CACHES_MAX_SIZE.
> > >
> > > When a memcg instance count is large enough it can lead
> > > to high order allocations up to order 7.
>
> This is definitely not nice and worth fixing! I am just wondering
> whether this is something you have encountered in the real life. Having
> thousands of memcgs sounds quite crazy^Wscary to me. I am not at all
> sure we are prepared for that and some controllers would have real
> issues with it AFAIR.
In our company we use custom-made lightweight container technology, the thing is
we can have up to several thousands of them on a server.
So those high-order allocations were observed on a real production workload.
> > > The same story with memcg_lrus allocations.
> > > So let's work this around by utilizing vmalloc fallback path.
> > >
> > > Signed-off-by: Anatoly Stepanov <astepanov@xxxxxxxxxxxxxx>
> > > ---
> > > include/linux/memcontrol.h | 16 ++++++++++++++++
> > > mm/list_lru.c | 14 +++++++-------
> > > mm/slab_common.c | 21 ++++++++++++++-------
> > > 3 files changed, 37 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > > index 61d20c1..a281622 100644
> > > --- a/include/linux/memcontrol.h
> > > +++ b/include/linux/memcontrol.h
> > > @@ -29,6 +29,9 @@
> > > #include <linux/mmzone.h>
> > > #include <linux/writeback.h>
> > > #include <linux/page-flags.h>
> > > +#include <linux/vmalloc.h>
> > > +#include <linux/slab.h>
> > > +#include <linux/mm.h>
> > >
> > > struct mem_cgroup;
> > > struct page;
> > > @@ -878,4 +881,17 @@ static inline void memcg_kmem_update_page_stat(struct page *page,
> > > }
> > > #endif /* CONFIG_MEMCG && !CONFIG_SLOB */
> > >
> > > +static inline void memcg_free(const void *ptr)
> > > +{
> > > + is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
> > > +}
> > > +
> > > +static inline void *memcg_alloc(size_t size)
> > > +{
> > > + if (likely(size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)))
>
> you are mixing two different units here...
>
> > > + return kzalloc(size, GFP_KERNEL|__GFP_NORETRY);
> > > +
> > > + return vzalloc(size);
> >
> > That's not how I imagine a "fallback" to work. You should be trying
> > kzalloc() and if that fails, call vzalloc(), not distinguish it by costly
> > order check. Also IIRC __GFP_NORETRY can easily fail even for non-costly
> > orders.
>
> Completely agreed! This should be done simply by
> gfp_t gfp_mask = GFP_KERNEL;
> void *ret;
>
> /*
> * Do not invoke OOM killer for larger requests as we can fall
> * back to the vmalloc
> */
> if (size > PAGE_SIZE)
> gfp_mask |= __GFP_NORETRY | __GFP_NOWARN;
I think we should check against PAGE_ALLOC_COSTLY_ORDER anyway,
as there's no big need to allocate large contiguous chunks here, at the same time someone
in the kernel might really need them.
>
> ret = kzalloc(size, gfp_mask);
> if (ret)
> return ret;
> return vzalloc(size);
>
> I also do not like memcg_alloc helper name. It suggests we are
> allocating a memcg while it is used for cache arrays and slab LRUS.
> Anyway this pattern is quite widespread in the kernel so I would simply
> suggest adding kvmalloc function instead.
Agreed, it would be nice to have a generic call.
I would suggest an impl. like this:
void *kvmalloc(size_t size)
{
gfp_t gfp_mask = GFP_KERNEL;
void *ret;
if (size > PAGE_SIZE)
gfp_mask |= __GFP_NORETRY | __GFP_NOWARN;
if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
ret = kzalloc(size, gfp_mask);
if (ret)
return ret;
}
return vzalloc(size);
}
> >
> > > +}
> > > +
> > > #endif /* _LINUX_MEMCONTROL_H */
> > > diff --git a/mm/list_lru.c b/mm/list_lru.c
> > > index 234676e..8f49339 100644
> > > --- a/mm/list_lru.c
> > > +++ b/mm/list_lru.c
> > > @@ -327,12 +327,12 @@ static int memcg_init_list_lru_node(struct list_lru_node *nlru)
> > > {
> > > int size = memcg_nr_cache_ids;
> > >
> > > - nlru->memcg_lrus = kmalloc(size * sizeof(void *), GFP_KERNEL);
> > > - if (!nlru->memcg_lrus)
> > > + nlru->memcg_lrus = memcg_alloc(size * sizeof(void *));
> > > + if (nlru->memcg_lrus == NULL)
> > > return -ENOMEM;
> > >
> > > if (__memcg_init_list_lru_node(nlru->memcg_lrus, 0, size)) {
> > > - kfree(nlru->memcg_lrus);
> > > + memcg_free(nlru->memcg_lrus);
> > > return -ENOMEM;
> > > }
> > >
> > > @@ -342,7 +342,7 @@ static int memcg_init_list_lru_node(struct list_lru_node *nlru)
> > > static void memcg_destroy_list_lru_node(struct list_lru_node *nlru)
> > > {
> > > __memcg_destroy_list_lru_node(nlru->memcg_lrus, 0, memcg_nr_cache_ids);
> > > - kfree(nlru->memcg_lrus);
> > > + memcg_free(nlru->memcg_lrus);
> > > }
> > >
> > > static int memcg_update_list_lru_node(struct list_lru_node *nlru,
> > > @@ -353,12 +353,12 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
> > > BUG_ON(old_size > new_size);
> > >
> > > old = nlru->memcg_lrus;
> > > - new = kmalloc(new_size * sizeof(void *), GFP_KERNEL);
> > > + new = memcg_alloc(new_size * sizeof(void *));
> > > if (!new)
> > > return -ENOMEM;
> > >
> > > if (__memcg_init_list_lru_node(new, old_size, new_size)) {
> > > - kfree(new);
> > > + memcg_free(new);
> > > return -ENOMEM;
> > > }
> > >
> > > @@ -375,7 +375,7 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
> > > nlru->memcg_lrus = new;
> > > spin_unlock_irq(&nlru->lock);
> > >
> > > - kfree(old);
> > > + memcg_free(old);
> > > return 0;
> > > }
> > >
> > > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > > index 329b038..19f8cb5 100644
> > > --- a/mm/slab_common.c
> > > +++ b/mm/slab_common.c
> > > @@ -157,9 +157,8 @@ static int init_memcg_params(struct kmem_cache *s,
> > > if (!memcg_nr_cache_ids)
> > > return 0;
> > >
> > > - arr = kzalloc(sizeof(struct memcg_cache_array) +
> > > - memcg_nr_cache_ids * sizeof(void *),
> > > - GFP_KERNEL);
> > > + arr = memcg_alloc(sizeof(struct memcg_cache_array) +
> > > + memcg_nr_cache_ids * sizeof(void *));
> > > if (!arr)
> > > return -ENOMEM;
> > >
> > > @@ -170,7 +169,15 @@ static int init_memcg_params(struct kmem_cache *s,
> > > static void destroy_memcg_params(struct kmem_cache *s)
> > > {
> > > if (is_root_cache(s))
> > > - kfree(rcu_access_pointer(s->memcg_params.memcg_caches));
> > > + memcg_free(rcu_access_pointer(s->memcg_params.memcg_caches));
> > > +}
> > > +
> > > +static void memcg_rcu_free(struct rcu_head *rcu)
> > > +{
> > > + struct memcg_cache_array *arr;
> > > +
> > > + arr = container_of(rcu, struct memcg_cache_array, rcu);
> > > + memcg_free(arr);
> > > }
> > >
> > > static int update_memcg_params(struct kmem_cache *s, int new_array_size)
> > > @@ -180,8 +187,8 @@ static int update_memcg_params(struct kmem_cache *s, int new_array_size)
> > > if (!is_root_cache(s))
> > > return 0;
> > >
> > > - new = kzalloc(sizeof(struct memcg_cache_array) +
> > > - new_array_size * sizeof(void *), GFP_KERNEL);
> > > + new = memcg_alloc(sizeof(struct memcg_cache_array) +
> > > + new_array_size * sizeof(void *));
> > > if (!new)
> > > return -ENOMEM;
> > >
> > > @@ -193,7 +200,7 @@ static int update_memcg_params(struct kmem_cache *s, int new_array_size)
> > >
> > > rcu_assign_pointer(s->memcg_params.memcg_caches, new);
> > > if (old)
> > > - kfree_rcu(old, rcu);
> > > + call_rcu(&old->rcu, memcg_rcu_free);
> > > return 0;
> > > }
> > >
> > >
>
> --
> Michal Hocko
> SUSE Labs
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