linux-kernel - Re: [PATCH] hv: Fix unnecessary sleeping in hv_synic

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Message-ID: <55fd96a5-84f1-0b0a-c8b7-601a96f387e6@gmail.com>
Date:   Mon, 18 Dec 2017 16:58:20 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        devel@...uxdriverproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hv: Fix unnecessary sleeping in hv_synic_alloc



On 2017/12/18 16:54, Vitaly Kuznetsov wrote:
> Jia-Ju Bai <baijiaju1990@...il.com> writes:
>
>> The kzalloc function is called with GFP_ATOMIC.
>> But according to driver call graph, it is not in atomic context,
>> namely no spinlock is held nor in an interrupt handler.
>>
>> This GFP_ATOMIC is unnecessary, and replace with GFP_KERNEL.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> ---
>>   drivers/hv/hv.c |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
>> index 8267439..b0d025a 100644
>> --- a/drivers/hv/hv.c
>> +++ b/drivers/hv/hv.c
>> @@ -150,7 +150,7 @@ int hv_synic_alloc(void)
>>   	int cpu;
>>
>>   	hv_context.hv_numa_map = kzalloc(sizeof(struct cpumask) * nr_node_ids,
>> -					 GFP_ATOMIC);
>> +					 GFP_KERNEL);
>>   	if (hv_context.hv_numa_map == NULL) {
>>   		pr_err("Unable to allocate NUMA map\n");
>>   		goto err;
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> The subject line is not very accurate: GFP_KERNEL you switch too is the
> one supporting 'sleep' when there's not enough memory, not
> GFP_ATOMIC so you don't actually "Fix unnecessary sleeping". I'd suggest
> you use something like "hyper-v: use GFP_KERNEL for hv_context.hv_numa_map"
>

Thanks for you suggestion :)
Okay, I found my description is not correct, too, sorry.
I will revise it and resubmit the patch.


Thanks,
Jia-Ju Bai