Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
On Fri, Jun 14, 2013 at 09:17:40AM +0800, Li Zefan wrote:
> >> static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> >> {
> >> + /*
> >> + * We need to call css_get() first, because memcg_uncharge_kmem()
> >> + * will call css_put() if it sees the memcg is dead.
> >> + */
> >> + smb_wmb();
> >>if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
> >>set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
> >
> > I do not feel strongly about that but maybe open coding this in
> > mem_cgroup_css_offline would be even better. There is only single caller
> > and there is smaller chance somebody will use the function incorrectly
> > later on.
> >
> > So I leave the decision on you because this doesn't matter much.
> >
>
> Yeah, it should go away soon. I'll post a patch after this patchset gets
> merged into -mm tree and then we can discuss there.
I don't care if it is open coded or not. If there is any strong preference
from anyone on this matter, feel free to change it.
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Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
>> static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
>> {
>> +/*
>> + * We need to call css_get() first, because memcg_uncharge_kmem()
>> + * will call css_put() if it sees the memcg is dead.
>> + */
>> +smb_wmb();
>> if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
>> set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
>
> I do not feel strongly about that but maybe open coding this in
> mem_cgroup_css_offline would be even better. There is only single caller
> and there is smaller chance somebody will use the function incorrectly
> later on.
>
> So I leave the decision on you because this doesn't matter much.
>
Yeah, it should go away soon. I'll post a patch after this patchset gets
merged into -mm tree and then we can discuss there.
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Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
On Thu, Jun 13, 2013 at 05:12:55PM +0800, Li Zefan wrote: > Sorry for updating the patchset so late. > > I've made some changes for the memory barrier thing, and I agree with > Michal that there can be improvement but can be a separate patch. > > If this version is ok for everyone, I'll send the whole patchset out > to Andrew. Can you please post an updated patch as reply to the original patch? It's a bit difficult to follow things. > = > > Use css_get/put instead of mem_cgroup_get/put. > > We can't do a simple replacement, because here mem_cgroup_put() > is called during mem_cgroup_css_free(), while mem_cgroup_css_free() > won't be called until css refcnt goes down to 0. > > Instead we increment css refcnt in mem_cgroup_css_offline(), and > then check if there's still kmem charges. If not, css refcnt will > be decremented immediately, otherwise the refcnt won't be decremented > when kmem charges goes down to 0. > > v3: > - changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(), > and added comment. > > v2: > - added wmb() in kmem_cgroup_css_offline(), pointed out by Michal > - revised comments as suggested by Michal > - fixed to check if kmem is activated in kmem_cgroup_css_offline() > > Signed-off-by: Li Zefan > Acked-by: Michal Hocko > Acked-by: KAMEZAWA Hiroyuki Reviewed-by: Tejun Heo But let's please remove the barrier dancing. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
[Fix Glauber's new address]
On Thu 13-06-13 17:53:19, Michal Hocko wrote:
> On Thu 13-06-13 17:12:55, Li Zefan wrote:
> > Sorry for updating the patchset so late.
> >
> > I've made some changes for the memory barrier thing, and I agree with
> > Michal that there can be improvement but can be a separate patch.
> >
> > If this version is ok for everyone, I'll send the whole patchset out
> > to Andrew.
> >
> > =
> >
> > Use css_get/put instead of mem_cgroup_get/put.
> >
> > We can't do a simple replacement, because here mem_cgroup_put()
> > is called during mem_cgroup_css_free(), while mem_cgroup_css_free()
> > won't be called until css refcnt goes down to 0.
> >
> > Instead we increment css refcnt in mem_cgroup_css_offline(), and
> > then check if there's still kmem charges. If not, css refcnt will
> > be decremented immediately,
>
> > otherwise the refcnt won't be decremented when kmem charges goes down
> > to 0.
>
> This is a bit confusing. What about "otherwise the css refcount will be
> released after the last kmem allocation is uncharged."
>
> >
> > v3:
> > - changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(),
> > and added comment.
> >
> > v2:
> > - added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
> > - revised comments as suggested by Michal
> > - fixed to check if kmem is activated in kmem_cgroup_css_offline()
> >
> > Signed-off-by: Li Zefan
> > Acked-by: Michal Hocko
> > Acked-by: KAMEZAWA Hiroyuki
> > ---
> > mm/memcontrol.c | 70
> > -
> > 1 file changed, 45 insertions(+), 25 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 466c595..76dcd0e 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -416,6 +416,11 @@ static void memcg_kmem_clear_activated(struct
> > mem_cgroup *memcg)
> >
> > static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> > {
> > + /*
> > +* We need to call css_get() first, because memcg_uncharge_kmem()
> > +* will call css_put() if it sees the memcg is dead.
> > +*/
> > + smb_wmb();
> > if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
> > set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
>
> I do not feel strongly about that but maybe open coding this in
> mem_cgroup_css_offline would be even better. There is only single caller
> and there is smaller chance somebody will use the function incorrectly
> later on.
>
> So I leave the decision on you because this doesn't matter much.
>
> [...]
> --
> Michal Hocko
> SUSE Labs
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majord...@vger.kernel.org
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--
Michal Hocko
SUSE Labs
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Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
On Thu 13-06-13 17:12:55, Li Zefan wrote:
> Sorry for updating the patchset so late.
>
> I've made some changes for the memory barrier thing, and I agree with
> Michal that there can be improvement but can be a separate patch.
>
> If this version is ok for everyone, I'll send the whole patchset out
> to Andrew.
>
> =
>
> Use css_get/put instead of mem_cgroup_get/put.
>
> We can't do a simple replacement, because here mem_cgroup_put()
> is called during mem_cgroup_css_free(), while mem_cgroup_css_free()
> won't be called until css refcnt goes down to 0.
>
> Instead we increment css refcnt in mem_cgroup_css_offline(), and
> then check if there's still kmem charges. If not, css refcnt will
> be decremented immediately,
> otherwise the refcnt won't be decremented when kmem charges goes down
> to 0.
This is a bit confusing. What about "otherwise the css refcount will be
released after the last kmem allocation is uncharged."
>
> v3:
> - changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(),
> and added comment.
>
> v2:
> - added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
> - revised comments as suggested by Michal
> - fixed to check if kmem is activated in kmem_cgroup_css_offline()
>
> Signed-off-by: Li Zefan
> Acked-by: Michal Hocko
> Acked-by: KAMEZAWA Hiroyuki
> ---
> mm/memcontrol.c | 70
> -
> 1 file changed, 45 insertions(+), 25 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 466c595..76dcd0e 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -416,6 +416,11 @@ static void memcg_kmem_clear_activated(struct mem_cgroup
> *memcg)
>
> static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> {
> + /*
> + * We need to call css_get() first, because memcg_uncharge_kmem()
> + * will call css_put() if it sees the memcg is dead.
> + */
> + smb_wmb();
> if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
> set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
I do not feel strongly about that but maybe open coding this in
mem_cgroup_css_offline would be even better. There is only single caller
and there is smaller chance somebody will use the function incorrectly
later on.
So I leave the decision on you because this doesn't matter much.
[...]
--
Michal Hocko
SUSE Labs
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[PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem
Sorry for updating the patchset so late.
I've made some changes for the memory barrier thing, and I agree with
Michal that there can be improvement but can be a separate patch.
If this version is ok for everyone, I'll send the whole patchset out
to Andrew.
=
Use css_get/put instead of mem_cgroup_get/put.
We can't do a simple replacement, because here mem_cgroup_put()
is called during mem_cgroup_css_free(), while mem_cgroup_css_free()
won't be called until css refcnt goes down to 0.
Instead we increment css refcnt in mem_cgroup_css_offline(), and
then check if there's still kmem charges. If not, css refcnt will
be decremented immediately, otherwise the refcnt won't be decremented
when kmem charges goes down to 0.
v3:
- changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(),
and added comment.
v2:
- added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
- revised comments as suggested by Michal
- fixed to check if kmem is activated in kmem_cgroup_css_offline()
Signed-off-by: Li Zefan
Acked-by: Michal Hocko
Acked-by: KAMEZAWA Hiroyuki
---
mm/memcontrol.c | 70 -
1 file changed, 45 insertions(+), 25 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 466c595..76dcd0e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -416,6 +416,11 @@ static void memcg_kmem_clear_activated(struct mem_cgroup
*memcg)
static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
{
+ /*
+* We need to call css_get() first, because memcg_uncharge_kmem()
+* will call css_put() if it sees the memcg is dead.
+*/
+ smb_wmb();
if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
}
@@ -3060,8 +3065,16 @@ static void memcg_uncharge_kmem(struct mem_cgroup
*memcg, u64 size)
if (res_counter_uncharge(&memcg->kmem, size))
return;
+ /*
+* Releases a reference taken in kmem_cgroup_css_offline in case
+* this last uncharge is racing with the offlining code or it is
+* outliving the memcg existence.
+*
+* The memory barrier imposed by test&clear is paired with the
+* explicit one in memcg_kmem_mark_dead().
+*/
if (memcg_kmem_test_and_clear_dead(memcg))
- mem_cgroup_put(memcg);
+ css_put(&memcg->css);
}
void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
@@ -5165,14 +5178,6 @@ static int memcg_update_kmem_limit(struct cgroup *cont,
u64 val)
* starts accounting before all call sites are patched
*/
memcg_kmem_set_active(memcg);
-
- /*
-* kmem charges can outlive the cgroup. In the case of slab
-* pages, for instance, a page contain objects from various
-* processes, so it is unfeasible to migrate them away. We
-* need to reference count the memcg because of that.
-*/
- mem_cgroup_get(memcg);
} else
ret = res_counter_set_limit(&memcg->kmem, val);
out:
@@ -5205,12 +5210,10 @@ static int memcg_propagate_kmem(struct mem_cgroup
*memcg)
goto out;
/*
-* destroy(), called if we fail, will issue static_key_slow_inc() and
-* mem_cgroup_put() if kmem is enabled. We have to either call them
-* unconditionally, or clear the KMEM_ACTIVE flag. I personally find
-* this more consistent, since it always leads to the same destroy path
+* __mem_cgroup_free() will issue static_key_slow_dec() because this
+* memcg is active already. If the later initialization fails then the
+* cgroup core triggers the cleanup so we do not have to do it here.
*/
- mem_cgroup_get(memcg);
static_key_slow_inc(&memcg_kmem_enabled_key);
mutex_lock(&set_limit_mutex);
@@ -5893,23 +5896,38 @@ static int memcg_init_kmem(struct mem_cgroup *memcg,
struct cgroup_subsys *ss)
return mem_cgroup_sockets_init(memcg, ss);
}
-static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
+static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
- mem_cgroup_sockets_destroy(memcg);
+ if (!memcg_kmem_is_active(memcg))
+ return;
+
+ /*
+* kmem charges can outlive the cgroup. In the case of slab
+* pages, for instance, a page contain objects from various
+* processes. As we prevent from taking a reference for every
+* such allocation we have to be careful when doing uncharge
+* (see memcg_uncharge_kmem) and here during offlining.
+*
+* The idea is that that only the _last_ uncharge which sees
+* the dead memcg will drop the last reference. An additional
+* reference is taken here befor
