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

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Date:	Tue, 19 Mar 2013 14:06:39 -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.

Does this actually help?  My memory is that /proc/vmcore did some magic
behind the scenes to combine these multiple note sections into a single
note section.

Certainly someone has to combine them together to make a valid elf
executable.

At the same time I don't see any harm in rounding up to a page size
here, but I don't see the point either.

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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