Re: 回复: [PATCH v3] debugobjects: install CPU hotplug callback

[Waiman Long]

On 9/9/20 9:48 PM, Zhang, Qiang wrote:
> ________________________________________
> 发件人: Waiman Long <longman@xxxxxxxxxx>
> 发送时间: 2020年9月9日 2:23
> 收件人: Zhang, Qiang; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; elver@xxxxxxxxxx
> 抄送: linux-kernel@xxxxxxxxxxxxxxx
> 主题: Re: [PATCH v3] debugobjects: install CPU hotplug callback
>
> On 9/8/20 2:27 AM, qiang.zhang@xxxxxxxxxxxxx wrote:
> > From: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> >
> > Due to CPU hotplug, it may never be online after it's offline,
> > some objects in percpu pool is never free. in order to avoid
> > this happening, install CPU hotplug callback, call this callback
> > func to free objects in percpu pool when CPU going offline.
> >
> > Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> > ---
> >    v1->v2:
> >    Modify submission information.
> >
> >    v2->v3:
> >    In CPU hotplug callback func, add clear percpu pool "obj_free" operation.
> >    capitalize 'CPU', and use shorter preprocessor sequence.
> >
> >    include/linux/cpuhotplug.h |  1 +
> >    lib/debugobjects.c         | 24 ++++++++++++++++++++++++
> >    2 files changed, 25 insertions(+)
> >
> > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> > index 3215023d4852..0c39d57e5342 100644
> > --- a/include/linux/cpuhotplug.h
> > +++ b/include/linux/cpuhotplug.h
> > @@ -36,6 +36,7 @@ enum cpuhp_state {
> >        CPUHP_X86_MCE_DEAD,
> >        CPUHP_VIRT_NET_DEAD,
> >        CPUHP_SLUB_DEAD,
> > +     CPUHP_DEBUG_OBJ_DEAD,
> >        CPUHP_MM_WRITEBACK_DEAD,
> >        CPUHP_MM_VMSTAT_DEAD,
> >        CPUHP_SOFTIRQ_DEAD,
> > diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> > index fe4557955d97..bb69a02c3e7b 100644
> > --- a/lib/debugobjects.c
> > +++ b/lib/debugobjects.c
> > @@ -19,6 +19,7 @@
> >    #include <linux/slab.h>
> >    #include <linux/hash.h>
> >    #include <linux/kmemleak.h>
> > +#include <linux/cpu.h>
> >
> >    #define ODEBUG_HASH_BITS    14
> >    #define ODEBUG_HASH_SIZE    (1 << ODEBUG_HASH_BITS)
> > @@ -433,6 +434,24 @@ static void free_object(struct debug_obj *obj)
> >        }
> >    }
> >
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +static int object_cpu_offline(unsigned int cpu)
> > +{
> > +     struct debug_percpu_free *percpu_pool;
> > +     struct hlist_node *tmp;
> > +     struct debug_obj *obj;
> > +
> > +     percpu_pool = per_cpu_ptr(&percpu_obj_pool, cpu);
> > +     hlist_for_each_entry_safe(obj, tmp, &percpu_pool->free_objs, node) {
> > +             hlist_del(&obj->node);
> > +             kmem_cache_free(obj_cache, obj);
> > +     }
> > +     percpu_pool->obj_free = 0;
> > > For pointer, it is better to use NULL for clarity.
> > > Cheers,
> > > Longman
> Do you mean "->obj_free" variable ?   this represents the number of free objects in  percpu_pool .
You are right. I got confused. Sorry for the noise.

Cheers,
Longman