linux-kernel - Re: [Resend][Bug fix PATCH v5] Reusing a resource structure allocated by bootmem

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Date:	Fri, 26 Apr 2013 10:57:38 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<hannes@...xchg.org>, <toshi.kani@...com>, <linuxram@...ibm.com>,
	<rientjes@...gle.com>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [Resend][Bug fix PATCH v5] Reusing a resource structure allocated
 by bootmem

2013/04/25 5:37, Andrew Morton wrote:
> On Wed, 24 Apr 2013 08:50:21 +0900 Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com> wrote:
>
>> When hot removing memory presented at boot time, following messages are shown:
>>
>> [  296.867031] ------------[ cut here ]------------
>> [  296.922273] kernel BUG at mm/slub.c:3409!
>>
>> ...
>>
>> The reason why the messages are shown is to release a resource structure,
>> allocated by bootmem, by kfree(). So when we release a resource structure,
>> we should check whether it is allocated by bootmem or not.
>>
>> But even if we know a resource structure is allocated by bootmem, we cannot
>> release it since SLxB cannot treat it. So for reusing a resource structure,
>> this patch remembers it by using bootmem_resource as follows:
>>
>> When releasing a resource structure by free_resource(), free_resource() checks
>> whether the resource structure is allocated by bootmem or not. If it is
>> allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
>> not allocated by bootmem, free_resource() release it by kfree().
>>
>> And when getting a new resource structure by get_resource(), get_resource()
>> checks whether bootmem_resource has released resource structures or not. If
>> there is a released resource structure, get_resource() returns it. If there is
>> not a releaed resource structure, get_resource() returns new resource structure
>> allocated by kzalloc().
>>
>> ...
>>
>
> Looks good to me.
>
>> --- 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 +51,14 @@ 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.
>> + */
>> +static struct resource *bootmem_resource_free;
>> +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 +160,40 @@ __initcall(ioresources_init);
>>
>>   #endif /* CONFIG_PROC_FS */
>>
>> +static void free_resource(struct resource *res)
>> +{
>> +	if (!res)
>> +		return;
>> +
>> +	if (!PageSlab(virt_to_head_page(res))) {
>
> Did you consider using a bit in resource.flags?  There appear to be
> four free ones left.  The VM trickery will work OK I guess, but isn't
> very "nice".
>
>> +		spin_lock(&bootmem_resource_lock);
>> +		res->sibling = bootmem_resource_free;
>> +		bootmem_resource_free = res;
>> +		spin_unlock(&bootmem_resource_lock);
>> +	} else {
>> +		kfree(res);
>> +	}
>> +}
>> +
>> +static struct resource *get_resource(gfp_t flags)
>> +{
>> +	struct resource *res = NULL;
>> +
>> +	spin_lock(&bootmem_resource_lock);
>> +	if (bootmem_resource_free) {
>> +		res = bootmem_resource_free;
>> +		bootmem_resource_free = res->sibling;
>> +	}
>> +	spin_unlock(&bootmem_resource_lock);
>> +
>> +	if (res)
>> +		memset(res, 0, sizeof(struct resource));
>> +	else
>> +		res = kzalloc(sizeof(struct resource), flags);
>> +
>> +	return res;
>> +}
>

> I think I'll rename this to alloc_resource().  In Linux "get" often
> (but not always) means "take a reference on".  So "get" pairs with
> "put" and "alloc" pairs with "free".

I forgot to answer it.
I think so too. And I have no objection about your update patch.

Thanks,
Yasuaki Ishimatsu

>
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