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Subject: Re: [PATCH v4 1/3] kexec: Move vmcoreinfo out of the kernel's .bss
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To: Dave Young <dyoung@redhat.com>, xlpang@redhat.com
Cc: Juergen Gross <jgross@suse.com>, linux-s390@vger.kernel.org,
        linux-ia64@vger.kernel.org, Baoquan He <bhe@redhat.com>,
        Petr Tesarik <ptesarik@suse.cz>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, Eric Biederman <ebiederm@xmission.com>,
        Hari Bathini <hbathini@linux.vnet.ibm.com>, akpm@linux-foundation.org,
        Michael Holzheu <holzheu@linux.vnet.ibm.com>
From: Xunlei Pang <xpang@redhat.com>
Message-ID: <59018AD6.5030403@redhat.com>
Date: Thu, 27 Apr 2017 14:08:22 +0800
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On 04/27/2017 at 01:44 PM, Dave Young wrote:
> Hi Xunlei,
>
> On 04/27/17 at 01:25pm, Xunlei Pang wrote:
>> On 04/27/2017 at 11:06 AM, Dave Young wrote:
>>> [snip]
>>>>>>>  
>>>>>>>  static int __init crash_save_vmcoreinfo_init(void)
>>>>>>>  {
>>>>>>> +	/* One page should be enough for VMCOREINFO_BYTES under all archs */
>>>>>> Can we add a comment in the VMCOREINFO_BYTES header file about the one
>>>>>> page assumption?
>>>>>>
>>>>>> Or just define the VMCOREINFO_BYTES as PAGE_SIZE instead of 4096
>>>>> Yes, I considered this before, but VMCOREINFO_BYTES is also used by VMCOREINFO_NOTE_SIZE
>>>>> definition which is exported to sysfs, also some platform has larger page size(64KB), so
>>>>> I didn't touch this 4096 value.
>>>>>
>>>>> I think I should use kmalloc() to allocate both of them, then move this comment to Patch3 
>>>>> kimage_crash_copy_vmcoreinfo().
>>>> But on the other hand, using a separate page for them seems safer compared with
>>>> using frequently-used slab, what's your opinion?
>>> I feel current page based way is better.
>>>
>>> For 64k page the vmcore note size will increase it seems fine. Do you
>>> have concern in mind?
>> Since tools are supposed to acquire vmcoreinfo note size from sysfs, it should be safe to do so,
>> except that there is some waste in memory for larger PAGE_SIZE.
> Either way is fine to me, I think it is up to your implementation, if
> choose page alloc then modify the macro with PAGE_SIZE looks better.

OK, I will use PAGE_SIZE then, thanks for your comments.

>
> Thanks
> Dave
>
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