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

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Message-ID: <20170427030607.GB10602@dhcp-128-65.nay.redhat.com>
Date:   Thu, 27 Apr 2017 11:06:07 +0800
From:   Dave Young <dyoung@...hat.com>
To:     xlpang@...hat.com
Cc:     Juergen Gross <jgross@...e.com>, linux-s390@...r.kernel.org,
        linux-ia64@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        kexec@...ts.infradead.org, Petr Tesarik <ptesarik@...e.cz>,
        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

[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?

Thanks