Subject: Re: [PATCH v4 3/8] foundations of per-cgroup memory pressure controlling.

From: Glauber Costa <[email-masked]>
Date: Tue, 4 Oct 2011 10:32:06 +0400

On 10/04/2011 04:57 AM, KAMEZAWA Hiroyuki wrote:
> On Mon,  3 Oct 2011 14:18:38 +0400
> Glauber Costa<[email-masked]>  wrote:
>
>> This patch converts struct sock fields memory_pressure,
>> memory_allocated, sockets_allocated, and sysctl_mem (now prot_mem)
>> to function pointers, receiving a struct mem_cgroup parameter.
>>
>> enter_memory_pressure is kept the same, since all its callers
>> have socket a context, and the kmem_cgroup can be derived from
>> the socket itself.
>>
>> To keep things working, the patch convert all users of those fields
>> to use acessor functions.
>>
>> In my benchmarks I didn't see a significant performance difference
>> with this patch applied compared to a baseline (around 1 % diff, thus
>> inside error margin).
>>
>> Signed-off-by: Glauber Costa<[email-masked]>
>> CC: David S. Miller<[email-masked]>
>> CC: Hiroyouki Kamezawa<[email-masked]>
>> CC: Eric W. Biederman<[email-masked]>
>
> A nitpick.
>
>
>>   #ifdef CONFIG_INET
>>   struct sock;
>> +struct proto;
>>   #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>>   void sock_update_memcg(struct sock *sk);
>>   void sock_release_memcg(struct sock *sk);
>> -
>> +void memcg_sock_mem_alloc(struct mem_cgroup *mem, struct proto *prot,
>> +			  int amt, int *parent_failure);
>> +void memcg_sock_mem_free(struct mem_cgroup *mem, struct proto *prot, int amt);
>> +void memcg_sockets_allocated_dec(struct mem_cgroup *mem, struct proto *prot);
>> +void memcg_sockets_allocated_inc(struct mem_cgroup *mem, struct proto *prot);
>>   #else
>> +/* memcontrol includes sockets.h, that includes memcontrol.h ... */
>> +static inline void memcg_sock_mem_alloc(struct mem_cgroup *mem,
>> +					struct proto *prot, int amt,
>> +					int *parent_failure)
>> +{
>> +}
>
> In these days, at naming memory cgroup pointers, we use "memcg" instead of
> "mem". So, could you use "memcg" for represeinting memory cgroup ?
>
>
>> +
>> +void memcg_sock_mem_alloc(struct mem_cgroup *mem, struct proto *prot,
>> +			  int amt, int *parent_failure)
>> +{
>> +	mem = parent_mem_cgroup(mem);
>> +	for (; mem != NULL; mem = parent_mem_cgroup(mem)) {
>> +		long alloc;
>> +		long *prot_mem = prot->prot_mem(mem);
>> +		/*
>> +		 * Large nestings are not the common case, and stopping in the
>> +		 * middle would be complicated enough, that we bill it all the
>> +		 * way through the root, and if needed, unbill everything later
>> +		 */
>> +		alloc = atomic_long_add_return(amt,
>> +					       prot->memory_allocated(mem));
>> +		*parent_failure |= (alloc>  prot_mem[2]);
>> +	}
>> +}
>> +EXPORT_SYMBOL(memcg_sock_mem_alloc);
>
> Hmm. why not using res_counter ? for reusing 'unbill' code ?
>
Well,

res_counters are slightly more expensive than needed here, since we need 
to clear interrupts and hold a spinlock. No particular reason besides it.

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