Re: [PATCH 2/2] mm: Create non-atomic version of SetPageReserved for init use

[Pasha Tatashin <Pavel.Tatashin@microsoft.com>]

On 9/5/18 4:18 PM, Alexander Duyck wrote:
> On Tue, Sep 4, 2018 at 11:24 PM Michal Hocko <mhocko@kernel.org> wrote:
>>
>> On Tue 04-09-18 11:33:45, Alexander Duyck wrote:
>>> From: Alexander Duyck <alexander.h.duyck@intel.com>
>>>
>>> It doesn't make much sense to use the atomic SetPageReserved at init time
>>> when we are using memset to clear the memory and manipulating the page
>>> flags via simple "&=" and "|=" operations in __init_single_page.
>>>
>>> This patch adds a non-atomic version __SetPageReserved that can be used
>>> during page init and shows about a 10% improvement in initialization times
>>> on the systems I have available for testing.
>>
>> I agree with Dave about a comment is due. I am also quite surprised that
>> this leads to such a large improvement. Could you be more specific about
>> your test and machines you were testing on?
> 
> So my test case has been just initializing 4 3TB blocks of persistent
> memory with a few trace_printk values added to track total time in
> move_pfn_range_to_zone.
> 
> What I have been seeing is that the time needed for the call drops on
> average from 35-36 seconds down to around 31-32.

Just curious why is there variance? During boot time is usually pretty
consistent, as there is only one thread and system is in pretty much the
same state.

A dmesg output in the commit log would be helpful.

Thank you,
Pavel

> 
>> Other than that the patch makes sense to me.
>>
>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>>
>> With the above addressed, feel free to add
>> Acked-by: Michal Hocko <mhocko@suse.com>
>>
>> Thanks!
> 
> As far as adding a comment are we just talking about why it is
> reserved, or do we need a description of the __SetPageReserved versus
> SetPageReserved. For now I was looking at adding a comment like:
> @@ -5517,8 +5517,13 @@ void __meminit memmap_init_zone(unsigned long
> size, int nid, unsigned long zone,
>  not_early:
>                 page = pfn_to_page(pfn);
>                 __init_single_page(page, pfn, zone, nid);
> +
> +               /*
> +                * Mark page reserved as it will need to wait for onlining
> +                * phase for it to be fully associated with a zone.
> +                */
>                 if (context == MEMMAP_HOTPLUG)
> -                       SetPageReserved(page);
> +                       __SetPageReserved(page);
> 
>                 /*
>                  * Mark the block movable so that blocks are reserved for
> 
> Any thoughts on this?
> 
> Thanks.
> 
> - Alex
>