linux-kernel - Re: [PATCH 4/6] kexec: improve the readability of crash_shrink

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Date:   Wed, 31 May 2023 15:48:30 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/6] kexec: improve the readability of
 crash_shrink_memory()

On 05/27/23 at 08:34pm, Zhen Lei wrote:
> The major adjustments are:
> 1. end = start + new_size.
>    The 'end' here is not an accurate representation, because it is not the
>    new end of crashk_res, but the start of ram_res, difference 1. So
>    eliminate it and replace it with ram_res->start.
> 2. Use 'ram_res->start' and 'ram_res->end' as arguments to
>    crash_free_reserved_phys_range() to indicate that the memory covered by
>    'ram_res' is released from the crashk. And keep it close to
>    insert_resource().
> 3. Replace 'if (start == end)' with 'if (!new_size)', clear indication that
>    all crashk memory will be shrunken.
> 
> No functional change.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>

LGTM,

Acked-by: Baoquan He <bhe@...hat.com>

> ---
>  kernel/kexec_core.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index bcc86a250ab3bf9..69fe92141b0b62d 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1108,7 +1108,6 @@ ssize_t crash_get_memory_size(void)
>  int crash_shrink_memory(unsigned long new_size)
>  {
>  	int ret = 0;
> -	unsigned long start, end;
>  	unsigned long old_size;
>  	struct resource *ram_res;
>  
> @@ -1119,9 +1118,7 @@ int crash_shrink_memory(unsigned long new_size)
>  		ret = -ENOENT;
>  		goto unlock;
>  	}
> -	start = crashk_res.start;
> -	end = crashk_res.end;
> -	old_size = (end == 0) ? 0 : end - start + 1;
> +	old_size = !crashk_res.end ? 0 : resource_size(&crashk_res);
>  	new_size = roundup(new_size, KEXEC_CRASH_MEM_ALIGN);
>  	if (new_size >= old_size) {
>  		ret = (new_size == old_size) ? 0 : -EINVAL;
> @@ -1134,22 +1131,20 @@ int crash_shrink_memory(unsigned long new_size)
>  		goto unlock;
>  	}
>  
> -	end = start + new_size;
> -	crash_free_reserved_phys_range(end, crashk_res.end);
> -
> -	ram_res->start = end;
> +	ram_res->start = crashk_res.start + new_size;
>  	ram_res->end = crashk_res.end;
>  	ram_res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
>  	ram_res->name = "System RAM";
>  
> -	if (start == end) {
> +	if (!new_size) {
>  		release_resource(&crashk_res);
>  		crashk_res.start = 0;
>  		crashk_res.end = 0;
>  	} else {
> -		crashk_res.end = end - 1;
> +		crashk_res.end = ram_res->start - 1;
>  	}
>  
> +	crash_free_reserved_phys_range(ram_res->start, ram_res->end);
>  	insert_resource(&iomem_resource, ram_res);
>  
>  unlock:
> -- 
> 2.25.1
>