linux-kernel - Re: [PATCH v3 12/21] vmcore: allocate per-cpu crash

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Date:	Tue, 19 Mar 2013 15:12:10 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	vgoyal@...hat.com, cpw@....com, kumagai-atsushi@....nes.nec.co.jp,
	lisa.mitchell@...com, heiko.carstens@...ibm.com,
	akpm@...ux-foundation.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, zhangyanfei@...fujitsu.com
Subject: Re: [PATCH v3 12/21] vmcore: allocate per-cpu crash_notes objects on page-size boundary

HATAYAMA Daisuke <d.hatayama@...fujitsu.com> writes:

> To satisfy mmap()'s page-size boundary requirement, allocate per-cpu
> crash_notes objects on page-size boundary.
>
> /proc/vmcore on the 2nd kernel checks if each note objects is
> allocated on page-size boundary. If there's some object not satisfying
> the page-size boundary requirement, /proc/vmcore doesn't provide
> mmap() interface.

On second look this requirement does not exist.  These all get copyied
into the unifed PT_NOTE segment so this patch is pointless and wrong.

I see no evidence of any need to change anything in the first kernel,
and this noticably increases the amount of memory used in the first
kernel and in the second kernel for no gain.

Eric

>
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
> ---
>
>  kernel/kexec.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index bddd3d7..d1f365e 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -1234,7 +1234,8 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
>  static int __init crash_notes_memory_init(void)
>  {
>  	/* Allocate memory for saving cpu registers. */
> -	crash_notes = alloc_percpu(note_buf_t);
> +	crash_notes = __alloc_percpu(roundup(sizeof(note_buf_t), PAGE_SIZE),
> +				     PAGE_SIZE);
>  	if (!crash_notes) {
>  		printk("Kexec: Memory allocation for saving cpu register"
>  		" states failed\n");
--
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