[Devel] [PATCH RHEL7] Removed warning from kmalloc in function alloc_rootdomain

[Denis V. Lunev]

On 7/3/20 7:19 PM, Denis V. Lunev wrote:
> On 7/3/20 7:12 PM, Valeriy Vdovin wrote:
>> 'alloc_rootdomain' is used during cpu hotplug actions when cpu's are
>> removed or added. So it's relatively rare occasion. The size of
>> allocated structure 'struct root_domain' is ~22k, which is a warnable
>> order 3. Because this structure is related to sched domain the code
>> accessing it is considered of high priority due to execution in
>> scheduling codepaths, so we should not fallback to virtualized page
>> continuity in this allocation and suppress order warning instead.
>>
>> Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
>> ---
>>  kernel/sched/core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 3fe0d62..8d14614 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -7141,7 +7141,7 @@ static struct root_domain *alloc_rootdomain(void)
>>  {
>>  	struct root_domain *rd;
>>  
>> -	rd = kmalloc(sizeof(*rd), GFP_KERNEL);
>> +	rd = kmalloc(sizeof(*rd), GFP_KERNEL | __GFP_ORDER_NOWARN);
>>  	if (!rd)
>>  		return NULL;
>>  
> NACK
>
> kvmalloc looks to me MUCH better. This item is no
> used in HW operations thus we could use virtually
> contiguous allocations.
>
> iris ~/src/git/linux-vz7 $ git diff
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3fe0d62cc51c..d1c489574284 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7051,7 +7051,7 @@ static void free_rootdomain(struct rcu_head *rcu)
>         free_cpumask_var(rd->rto_mask);
>         free_cpumask_var(rd->online);
>         free_cpumask_var(rd->span);
> -       kfree(rd);
> +       kvfree(rd);
>  }
>  
>  static void rq_attach_root(struct rq *rq, struct root_domain *rd)
> @@ -7141,12 +7141,12 @@ static struct root_domain *alloc_rootdomain(void)
>  {
>         struct root_domain *rd;
>  
> -       rd = kmalloc(sizeof(*rd), GFP_KERNEL);
> +       rd = kvmalloc(sizeof(*rd), GFP_KERNEL);
>         if (!rd)
>                 return NULL;
>  
>         if (init_rootdomain(rd) != 0) {
> -               kfree(rd);
> +               kvfree(rd);
>                 return NULL;
>         }
>  
> iris ~/src/git/linux-vz7 $
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commit 4dac0b638310d2e92f6e19958b73d4c97c9734bb
Author: Peter Zijlstra <peterz at infradead.org>
Date:   Wed May 14 16:04:26 2014 +0200

    sched/cpupri: Replace NR_CPUS arrays
   
    Tejun reported that his resume was failing due to order-3 allocations
    from sched_domain building.
   
    Replace the NR_CPUS arrays in there with a dynamically allocated
    array.
   
    Reported-by: Tejun Heo <tj at kernel.org>
    Signed-off-by: Peter Zijlstra <peterz at infradead.org>
    Cc: Johannes Weiner <hannes at cmpxchg.org>
    Cc: Steven Rostedt <rostedt at goodmis.org>
    Cc: Linus Torvalds <torvalds at linux-foundation.org>
    Link:
http://lkml.kernel.org/n/tip-7cysnkw1gik45r864t1nkudh@git.kernel.org
    Signed-off-by: Ingo Molnar <mingo at kernel.org>