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

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Date:   Fri, 22 Sep 2023 11:08:31 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Yajun Deng <yajun.deng@...ux.dev>, 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 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.

> -- 
> Cheers,
> 
> David / dhildenb
> 

-- 
Sincerely yours,
Mike.