linux-kernel - Re: [PATCH 1/2] mm: Replace nr_node_ids for loop with for_each

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Message-ID: <55F6C637.6080807@linux.vnet.ibm.com>
Date:	Mon, 14 Sep 2015 18:35:59 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
CC:	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	anton@...ba.org, akpm@...ux-foundation.org,
	nacc@...ux.vnet.ibm.com, gkurz@...ux.vnet.ibm.com,
	zhong@...ux.vnet.ibm.com, grant.likely@...aro.org,
	nikunj@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH  1/2] mm: Replace nr_node_ids for loop with for_each_node
 in list lru

On 09/14/2015 05:34 PM, Vladimir Davydov wrote:
> On Mon, Sep 14, 2015 at 05:09:31PM +0530, Raghavendra K T wrote:
>> On 09/14/2015 02:30 PM, Vladimir Davydov wrote:
>>> On Wed, Sep 09, 2015 at 12:01:46AM +0530, Raghavendra K T wrote:
>>>> The functions used in the patch are in slowpath, which gets called
>>>> whenever alloc_super is called during mounts.
>>>>
>>>> Though this should not make difference for the architectures with
>>>> sequential numa node ids, for the powerpc which can potentially have
>>>> sparse node ids (for e.g., 4 node system having numa ids, 0,1,16,17
>>>> is common), this patch saves some unnecessary allocations for
>>>> non existing numa nodes.
>>>>
>>>> Even without that saving, perhaps patch makes code more readable.
>>>
>>> Do I understand correctly that node 0 must always be in
>>> node_possible_map? I ask, because we currently test
>>> lru->node[0].memcg_lrus to determine if the list is memcg aware.
>>>
>>
>> Yes, node 0 is always there. So it should not be a problem.
>
> I think it should be mentioned in the comment to list_lru_memcg_aware
> then.
>

Something like this: ?
static inline bool list_lru_memcg_aware(struct list_lru *lru)
{
         /*
          * This needs node 0 to be always present, even
          * in the systems supporting sparse numa ids.
          */
         return !!lru->node[0].memcg_lrus;
}


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