linux-kernel - Re: [PATCH 1/4] mm: pass set_count and set_reserved to __init_single

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Date:   Mon, 25 Sep 2023 11:23:03 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com, muchun.song@...ux.dev, glider@...gle.com,
        elver@...gle.com, dvyukov@...gle.com, osalvador@...e.de,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH 1/4] mm: pass set_count and set_reserved to
 __init_single_page


On 2023/9/22 16:08, Mike Rapoport wrote:
> On Fri, Sep 22, 2023 at 09:48:59AM +0200, David Hildenbrand wrote:
>> On 22.09.23 09:47, Matthew Wilcox wrote:
>>> On Fri, Sep 22, 2023 at 03:09:20PM +0800, Yajun Deng wrote:
>>>> -		__init_single_page(page, pfn, zone, nid);
>>>> +		__init_single_page(page, pfn, zone, nid, true, false);
>>> So Linus has just had a big rant about not doing bool flags to
>>> functions.  And in particular _multiple_ bool flags to functions.
>>>
>>> ie this should be:
>>>
>>> #define INIT_PAGE_COUNT		(1 << 0)
>>> #define INIT_PAGE_RESERVED	(1 << 1)
>>>
>>> 		__init_single_page(page, pfn, zone, nid, INIT_PAGE_COUNT);
>>>
>>> or something similar.
>>>
>>> I have no judgement on the merits of this patch so far.  Do you have
>>> performance numbers for each of these patches?  Some of them seem quite
>>> unlikely to actually help, at least on a machine which is constrained
>>> by cacheline fetches.
>> The last patch contains
>>
>> before:
>> node 0 deferred pages initialised in 78ms
>>
>> after:
>> node 0 deferred pages initialised in 72ms
>>
>> Not earth-shattering :D Maybe with much bigger machines relevant?
> Patch 3 contains
>
> The following data was tested on an x86 machine with 190GB of RAM.
>
> before:
> free_low_memory_core_early()    342ms
>
> after:
> free_low_memory_core_early()    286ms
>
> Which is more impressive, but still I'm not convinced that it's worth the
> added complexity and potential subtle bugs.
>
I will send v2.  It will be simpler and safer.
>> -- 
>> Cheers,
>>
>> David / dhildenb
>>