linux-kernel - Re: [PATCH v4 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section

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Message-ID: <590180AF.3030202@redhat.com>
Date:   Thu, 27 Apr 2017 13:25:03 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Dave Young <dyoung@...hat.com>, xlpang@...hat.com
Cc:     Juergen Gross <jgross@...e.com>, linux-s390@...r.kernel.org,
        linux-ia64@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        Petr Tesarik <ptesarik@...e.cz>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        akpm@...ux-foundation.org,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 1/3] kexec: Move vmcoreinfo out of the kernel's .bss
 section

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.

Regards,
Xunlei