linux-kernel - Re: [Bug fix PATCH v4] Reusing a resource structure allocated by bootmem

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Date:	Fri, 19 Apr 2013 08:33:13 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	<akpm@...ux-foundation.org>, <linuxram@...ibm.com>,
	<rientjes@...gle.com>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [Bug fix PATCH v4] Reusing a resource structure allocated by
 bootmem

Hi Toshi,

2013/04/18 23:23, Toshi Kani wrote:
> On Thu, 2013-04-18 at 17:36 +0900, Yasuaki Ishimatsu wrote:
>> When hot removing memory presented at boot time, following messages are shown:
>   :
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index 4aef886..637e8d2 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -21,6 +21,7 @@
>>   #include <linux/seq_file.h>
>>   #include <linux/device.h>
>>   #include <linux/pfn.h>
>> +#include <linux/mm.h>
>>   #include <asm/io.h>
>>
>>
>> @@ -50,6 +51,16 @@ struct resource_constraint {
>>
>>   static DEFINE_RWLOCK(resource_lock);
>>
>> +/*
>> + * For memory hotplug, there is no way to free resource entries allocated
>> + * by boot mem after the system is up. So for reusing the resource entry
>> + * we need to remember the resource.
>> + */
>> +struct resource bootmem_resource = {
>> +	.sibling = NULL,
>> +};
>

> This should be a pointer of struct resource and declared as static, such
> as:
>
> static struct resource *bootmem_resource_free;

O.K. I'll update it.

>
>> +static DEFINE_SPINLOCK(bootmem_resource_lock);
>> +
>>   static void *r_next(struct seq_file *m, void *v, loff_t *pos)
>>   {
>>   	struct resource *p = v;
>> @@ -151,6 +162,39 @@ __initcall(ioresources_init);
>>
>>   #endif /* CONFIG_PROC_FS */
>>
>> +static void free_resource(struct resource *res)
>> +{
>> +	if (!res)
>> +		return;
>> +
>> +	if (PageSlab(virt_to_head_page(res))) {
>> +		spin_lock(&bootmem_resource_lock);
>> +		res->sibling = bootmem_resource.sibling;
>> +		bootmem_resource.sibling = res;
>> +		spin_unlock(&bootmem_resource_lock);
>> +	} else {
>> +		kfree(res);
>> +	}
>> +}
>

> I second with Johannes.

I'll update it.

>
>> +static struct resource *get_resource(gfp_t flags)
>> +{
>> +	struct resource *res = NULL;
>> +
>> +	spin_lock(&bootmem_resource_lock);
>> +	if (bootmem_resource.sibling) {
>> +		res = bootmem_resource.sibling;
>> +		bootmem_resource.sibling = res->sibling;
>> +		memset(res, 0, sizeof(struct resource));
>> +	}
>> +	spin_unlock(&bootmem_resource_lock);
>

> I prefer to keep memset() outside of the spin lock.
>
> spin_lock(&bootmem_resource_lock);
> if (..) {
> 	:
> 	spin_unlock(&bootmem_resource_lock);
> 	memset(res, 0, sizeof(struct resource));
> } else {
> 	spin_unlock(&bootmem_resource_lock);
> 	res = kzalloc(sizeof(struct resource), flags);
> }

Hmm. It is a little ugly. How about it?

spin_lock(&bootmem_resource_lock);
if (bootmem_resource.sibling) {
	res = bootmem_resource.sibling;
	bootmem_resource.sibling = res->sibling;
}
spin_unlock(&bootmem_resource_lock);

if (res)
	memset(res, 0, sizeof(struct resource));
else	
	res = kzalloc(sizeof(struct resource), flags);

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> -Toshi
>
>> +
>> +
>> +	return res;
>> +}
>> +
>
>


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