[Devel] Re: [PATCH 4/8] RSS container core

[Pavel Emelianov]

Andrew Morton wrote:
>> +#else
>> +static inline int container_rss_prepare(struct page *pg,
>> +		struct vm_area_struct *vma, struct page_container **pc)
>> +{
>> +	*pc = NULL; /* to make gcc happy */
> 
> eh?  What is gcc's problem here?

When this line is missed and CONFIG_RSS_COUNTER is n the following
warnings are produced:

  CC      mm/memory.o
mm/memory.c: In function ‘__do_fault’:
mm/memory.c:2472: warning: ‘pcont’ is used uninitialized in this function
mm/memory.c: In function ‘do_wp_page’:
mm/memory.c:1788: warning: ‘pcont’ is used uninitialized in this function
mm/memory.c: In function ‘__handle_mm_fault’:
mm/memory.c:2317: warning: ‘pcont’ is used uninitialized in this function
mm/memory.c:2253: warning: ‘pcont’ is used uninitialized in this function

>> +	return 0;
>> +}
>>
>> ...
>>
>> +static int rss_populate(struct container_subsys *ss,
>> +		struct container *cont)
>> +{
>> +	int rc;
>> +
>> +	if ((rc = container_add_file(cont, &rss_usage)) < 0)
>> +		return rc;
>> +	if ((rc = container_add_file(cont, &rss_failcnt)) < 0)
>> +		return rc;
>> +	if ((rc = container_add_file(cont, &rss_limit)) < 0)
>> +		return rc;
>> +	if ((rc = container_add_file(cont, &rss_reclaimed)) < 0)
>> +		return rc;
> 
> If we fail partway through here, do the thus-far-created fiels get cleaned up?

Yes. As far as I see from Paul's code when one of the files is failed to
be created the whole container is cleaned up.

>> +	return 0;
>> +}
>> +
>> +struct container_subsys rss_subsys = {
>> +	.name = "rss",
>> +	.subsys_id = rss_subsys_id,
>> +	.create = rss_create,
>> +	.destroy = rss_destroy,
>> +	.populate = rss_populate,
>> +	.attach = rss_move_task,
>> +	.early_init = 1,
>> +};
> 
> Did this need kernel-wide scope?

Yes. In include/linux/countainer_subsys.h we declared the SUBSYS(rss) 
that is expanded into "extern struct container_subsys rss_subsys;" in the
kernel/container.c file. Further the pointer to it is injected into the array
of subsystems (static struct container_subsys *subsys[]; at the top of the file).