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

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Message-ID: <5175D37D.2070100@jp.fujitsu.com>
Date:	Tue, 23 Apr 2013 09:19:09 +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

2013/04/19 23:30, Toshi Kani wrote:
> On Fri, 2013-04-19 at 17:09 +0900, Yasuaki Ishimatsu wrote:
>> Hi Toshi,
>>
>> 2013/04/19 8:33, Yasuaki Ishimatsu wrote:
>>> 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.
>>
>> Oh, I missed "should be pointer of struct resource" part.
>> Please teach me your detailed idea. If this is defined as pointer,
>> how do we initialize this and manage bootmem resources?
>>
>> I'm thinking it but have no idea.
>

> Sure.  It's quite simple.  Since only bootmem_resource.sibling is used,
> it can be replaced with a pointer, such as bootmem_resource_free.  This
> avoids allocating a struct resource table as this code is supposed to
> save memory.
>
> So, first, declare the pointer below, which is initialized to NULL as
> BSS (checkpatch.pl complains if you set it to NULL explicitly).
>
>    static struct resource *bootmem_resource_free;
>
> Then, in free_resource(), this pointer replaces bootmem_resource.sibling
> as follows.
>
>    res->sibling = bootmem_resource_free;
>    bootmem_resource_free = res;
>
> Similarly, in get_resource().
>
>    if (bootmem_resource_free) {
>        res = bootmem_resource_free;
>        bootmem_resource_free = res->sibling;
>    }

Thank you for your detail explanation. I clearly understood your idea.
I'll update your comment and post a updated patch.

Thanks,
Yasuaki Ishimatsu

>
>
> Thanks,
> -Toshi
>


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