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

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Date:   Wed, 09 Jan 2019 11:28:52 +0530
From:   Arun KS <arunks@...eaurora.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        arunks.linux@...il.com, akpm@...ux-foundation.org, 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 2019-01-08 23:43, Michal Hocko wrote:
> On Tue 08-01-19 09:56:09, Alexander Duyck wrote:
>> On Fri, 2019-01-04 at 10:31 +0530, Arun KS wrote:
> [...]
>> >  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);
>> 
>> Shouldn't this be a "+=" instead of an "="? It seems like you are 
>> going
>> to lose your count otherwise.
> 
> You are right of course. I should have noticed during the review.
> Thanks!

I think we don't need to. The caller function is setting onlined_pages = 
0 before calling online_pages_range().
And there are no other reference to online_pages_range other than from 
online_pages().

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memory_hotplug.c?h=v5.0-rc1#n845

int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int 
online_type)
{
         unsigned long flags;
         unsigned long onlined_pages = 0;

Regards,
Arun