linux-kernel - Re: [PATCH] mm/memory_hotplug: Drop 'reason' argument from check_pfn

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Message-ID: <Yo3n8Zagb68zuMqa@localhost.localdomain>
Date:   Wed, 25 May 2022 10:25:21 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memory_hotplug: Drop 'reason' argument from
 check_pfn_span()

On Wed, May 25, 2022 at 09:09:09AM +0530, Anshuman Khandual wrote:
> In check_pfn_span(), a 'reason' string is being used to recreate the caller
> function name, while printing the warning message. It is really unnecessary
> as the warning message could just be printed inside the caller depending on
> the return code. Currentlyy there are just two callers for check_pfn_span()
                   Currently
> i.e  __add_pages() and __remove_pages(). Let's clean this up.
> 
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>

One could argue if this is really a cleanup.
I kind of agree that the "reason" thingy is a bit shaky, but instead of having a
single place where we call WARN(), we now do have two.

> ---
>  mm/memory_hotplug.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 416b38ca8def..9b3d7295ef93 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -220,8 +220,7 @@ static void release_memory_resource(struct resource *res)
>  	kfree(res);
>  }
>  
> -static int check_pfn_span(unsigned long pfn, unsigned long nr_pages,
> -		const char *reason)
> +static int check_pfn_span(unsigned long pfn, unsigned long nr_pages)
>  {
>  	/*
>  	 * Disallow all operations smaller than a sub-section and only
> @@ -238,12 +237,8 @@ static int check_pfn_span(unsigned long pfn, unsigned long nr_pages,
>  		min_align = PAGES_PER_SUBSECTION;
>  	else
>  		min_align = PAGES_PER_SECTION;
> -	if (!IS_ALIGNED(pfn, min_align)
> -			|| !IS_ALIGNED(nr_pages, min_align)) {
> -		WARN(1, "Misaligned __%s_pages start: %#lx end: #%lx\n",
> -				reason, pfn, pfn + nr_pages - 1);
> +	if (!IS_ALIGNED(pfn, min_align) || !IS_ALIGNED(nr_pages, min_align))
>  		return -EINVAL;
> -	}
>  	return 0;
>  }
>  
> @@ -320,9 +315,11 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
>  		altmap->alloc = 0;
>  	}
>  
> -	err = check_pfn_span(pfn, nr_pages, "add");
> -	if (err)
> +	err = check_pfn_span(pfn, nr_pages);
> +	if (err) {
> +		WARN(1, "Misaligned %s start: %#lx end: #%lx\n", __func__, pfn, pfn + nr_pages - 1);
>  		return err;
> +	}

If you want to further clean this up, I would just do 

 if (check_pfn_span()) {
         WARN(....)
         return -EINVAL;
 }

here as we do in __remove_pages(). check_pfn_span() can either return 0 or -EINVAL,
so I think it is fine.


-- 
Oscar Salvador
SUSE Labs