[Devel] Re: [PATCH v2 07/11] mm: Allocate kernel pages to the right memcg

[Glauber Costa]

On 08/10/2012 09:36 PM, Greg Thelen wrote:
> On Thu, Aug 09 2012, Glauber Costa wrote:
> 
>> When a process tries to allocate a page with the __GFP_KMEMCG flag, the
>> page allocator will call the corresponding memcg functions to validate
>> the allocation. Tasks in the root memcg can always proceed.
>>
>> To avoid adding markers to the page - and a kmem flag that would
>> necessarily follow, as much as doing page_cgroup lookups for no reason,
>> whoever is marking its allocations with __GFP_KMEMCG flag is responsible
>> for telling the page allocator that this is such an allocation at
>> free_pages() time. This is done by the invocation of
>> __free_accounted_pages() and free_accounted_pages().
>>
>> Signed-off-by: Glauber Costa <glommer at parallels.com>
>> CC: Christoph Lameter <cl at linux.com>
>> CC: Pekka Enberg <penberg at cs.helsinki.fi>
>> CC: Michal Hocko <mhocko at suse.cz>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
>> CC: Johannes Weiner <hannes at cmpxchg.org>
>> CC: Suleiman Souhlal <suleiman at google.com>
>> ---
>>  include/linux/gfp.h |  3 +++
>>  mm/page_alloc.c     | 38 ++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 41 insertions(+)
>>
>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>> index d8eae4d..029570f 100644
>> --- a/include/linux/gfp.h
>> +++ b/include/linux/gfp.h
>> @@ -370,6 +370,9 @@ extern void free_pages(unsigned long addr, unsigned int order);
>>  extern void free_hot_cold_page(struct page *page, int cold);
>>  extern void free_hot_cold_page_list(struct list_head *list, int cold);
>>  
>> +extern void __free_accounted_pages(struct page *page, unsigned int order);
>> +extern void free_accounted_pages(unsigned long addr, unsigned int order);
>> +
>>  #define __free_page(page) __free_pages((page), 0)
>>  #define free_page(addr) free_pages((addr), 0)
>>  
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index b956cec..da341dc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2532,6 +2532,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>>  	struct page *page = NULL;
>>  	int migratetype = allocflags_to_migratetype(gfp_mask);
>>  	unsigned int cpuset_mems_cookie;
>> +	void *handle = NULL;
>>  
>>  	gfp_mask &= gfp_allowed_mask;
>>  
>> @@ -2543,6 +2544,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>>  		return NULL;
>>  
>>  	/*
>> +	 * Will only have any effect when __GFP_KMEMCG is set.
>> +	 * This is verified in the (always inline) callee
>> +	 */
>> +	if (!memcg_kmem_new_page(gfp_mask, &handle, order))
>> +		return NULL;
>> +
>> +	/*
>>  	 * Check the zones suitable for the gfp_mask contain at least one
>>  	 * valid zone. It's possible to have an empty zonelist as a result
>>  	 * of GFP_THISNODE and a memoryless node
>> @@ -2583,6 +2591,8 @@ out:
>>  	if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
>>  		goto retry_cpuset;
>>  
>> +	memcg_kmem_commit_page(page, handle, order);
>> +
>>  	return page;
>>  }
>>  EXPORT_SYMBOL(__alloc_pages_nodemask);
>> @@ -2635,6 +2645,34 @@ void free_pages(unsigned long addr, unsigned int order)
>>  
>>  EXPORT_SYMBOL(free_pages);
>>  
>> +/*
>> + * __free_accounted_pages and free_accounted_pages will free pages allocated
>> + * with __GFP_KMEMCG.
>> + *
>> + * Those pages are accounted to a particular memcg, embedded in the
>> + * corresponding page_cgroup. To avoid adding a hit in the allocator to search
>> + * for that information only to find out that it is NULL for users who have no
>> + * interest in that whatsoever, we provide these functions.
>> + *
>> + * The caller knows better which flags it relies on.
>> + */
>> +void __free_accounted_pages(struct page *page, unsigned int order)
>> +{
>> +	memcg_kmem_free_page(page, order);
>> +	__free_pages(page, order);
>> +}
>> +EXPORT_SYMBOL(__free_accounted_pages);
>> +
>> +void free_accounted_pages(unsigned long addr, unsigned int order)
>> +{
>> +	if (addr != 0) {
>> +		VM_BUG_ON(!virt_addr_valid((void *)addr));
>> +		memcg_kmem_free_page(virt_to_page((void *)addr), order);
>> +		__free_pages(virt_to_page((void *)addr), order);
> 
> Nit.  Is there any reason not to replace the above two lines with:
> 		__free_accounted_pages(virt_to_page((void *)addr), order);
> 
Not any particular reason. If people prefer it this way, I can do that
with no problems.