linux-kernel - Re: [PATCH v7] mm/page_alloc.c: memory_hotplug: free pages as higher order

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Message-ID: <51ebe46608c1b502bb7985498f29302d@codeaurora.org>
Date:   Thu, 10 Jan 2019 10:36:43 +0530
From:   Arun KS <arunks@...eaurora.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        arunks.linux@...il.com, vbabka@...e.cz, osalvador@...e.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        getarunks@...il.com
Subject: Re: [PATCH v7] mm/page_alloc.c: memory_hotplug: free pages as higher
 order

On 2019-01-10 00:26, Andrew Morton wrote:
> On Wed, 09 Jan 2019 16:36:36 +0530 Arun KS <arunks@...eaurora.org> 
> wrote:
> 
>> On 2019-01-09 16:27, Michal Hocko wrote:
>> > On Wed 09-01-19 16:12:48, Arun KS wrote:
>> > [...]
>> >> It will be called once per online of a section and the arg value is
>> >> always
>> >> set to 0 while entering online_pages_range.
>> >
>> > You rare right that this will be the case in the most simple scenario.
>> > But the point is that the callback can be called several times from
>> > walk_system_ram_range and then your current code wouldn't work
>> > properly.
>> 
>> Thanks. Will use +=
> 
> The v8 patch
> https://lore.kernel.org/lkml/1547032395-24582-1-git-send-email-arunks@codeaurora.org/T/#u
> 
> (which you apparently sent 7 minutes after typing the above) still has
> 
>  static int online_pages_range(unsigned long start_pfn, unsigned long 
> nr_pages,
>  			void *arg)
>  {
> -	unsigned long i;
>  	unsigned long onlined_pages = *(unsigned long *)arg;
> -	struct page *page;
> 
>  	if (PageReserved(pfn_to_page(start_pfn)))
> -		for (i = 0; i < nr_pages; i++) {
> -			page = pfn_to_page(start_pfn + i);
> -			(*online_page_callback)(page);
> -			onlined_pages++;
> -		}
> +		onlined_pages = online_pages_blocks(start_pfn, nr_pages);
> 
> 
> Even then the code makes no sense.
> 
> static int online_pages_range(unsigned long start_pfn, unsigned long 
> nr_pages,
> 			void *arg)
> {
> 	unsigned long onlined_pages = *(unsigned long *)arg;
> 
> 	if (PageReserved(pfn_to_page(start_pfn)))
> 		onlined_pages += online_pages_blocks(start_pfn, nr_pages);
> 
> 	online_mem_sections(start_pfn, start_pfn + nr_pages);
> 
> 	*(unsigned long *)arg += onlined_pages;
> 	return 0;
> }
> 
> Either the final assignment should be
> 
> 	*(unsigned long *)arg = onlined_pages;
> 
> or the initialization should be
> 
> 	unsigned long onlined_pages = 0;
> 
> 
> 
> This is becoming a tad tiresome and I'd prefer not to have to check up
> on such things.  Can we please get this right?

Sorry about that. Will fix it.

Regards,
Arun