linux-kernel - Re: [PATCH 2/3] mm: calculate deferred pages after skipping mirrored memory

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Date:   Wed, 25 Jul 2018 14:14:59 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        linux-mm@...ck.org, dan.j.williams@...el.com, jack@...e.cz,
        jglisse@...hat.com, jrdr.linux@...il.com, bhe@...hat.com,
        gregkh@...uxfoundation.org, vbabka@...e.cz,
        richard.weiyang@...il.com, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH 2/3] mm: calculate deferred pages after skipping mirrored
 memory

On Tue, Jul 24, 2018 at 07:55:19PM -0400, Pavel Tatashin wrote:
> update_defer_init() should be called only when struct page is about to be
> initialized. Because it counts number of initialized struct pages, but
> there we may skip struct pages if there is some mirrored memory.
> 
> So move, update_defer_init() after checking for mirrored memory.
> 
> Also, rename update_defer_init() to defer_init() and reverse the return
> boolean to emphasize that this is a boolean function, that tells that the
> reset of memmap initialization should be deferred.
> 
> Make this function self-contained: do not pass number of already
> initialized pages in this zone by using static counters.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> ---
>  mm/page_alloc.c | 40 ++++++++++++++++++++--------------------
>  1 file changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cea749b26394..86c678cec6bd 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -306,24 +306,28 @@ static inline bool __meminit early_page_uninitialised(unsigned long pfn)
>  }
>  
>  /*
> - * Returns false when the remaining initialisation should be deferred until
> + * Returns true when the remaining initialisation should be deferred until
>   * later in the boot cycle when it can be parallelised.
>   */
> -static inline bool update_defer_init(pg_data_t *pgdat,
> -				unsigned long pfn, unsigned long zone_end,
> -				unsigned long *nr_initialised)
> +static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>  {
> +	static unsigned long prev_end_pfn, nr_initialised;
> +
> +	if (prev_end_pfn != end_pfn) {
> +		prev_end_pfn = end_pfn;
> +		nr_initialised = 0;
> +	}
Hi Pavel,

What about a comment explaining that "if".
I am not the brightest one, so it took me a bit to figure out that we got that "if" there
because now that the variables are static, we need to somehow track whenever we change to
another zone.

Thanks
-- 
Oscar Salvador
SUSE L3