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Subject: Re: [PATCH] mm, memory_hotplug: update pcp lists everytime onlining a
 memory block
To:     Charan Teja Reddy <charante@codeaurora.org>,
        akpm@linux-foundation.org, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, vinmenon@codeaurora.org
References: <1596372896-15336-1-git-send-email-charante@codeaurora.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <b9502c00-521c-5b13-9c31-fd2da12bff6c@suse.cz>
Date:   Mon, 3 Aug 2020 15:55:21 +0200
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On 8/2/20 2:54 PM, Charan Teja Reddy wrote:
> When onlining a first memory block in a zone, pcp lists are not updated
> thus pcp struct will have the default setting of ->high = 0,->batch = 1.
> This means till the second memory block in a zone(if it have) is onlined
> the pcp lists of this zone will not contain any pages because pcp's
> ->count is always greater than ->high thus free_pcppages_bulk() is
> called to free batch size(=1) pages every time system wants to add a
> page to the pcp list through free_unref_page(). To put this in a word,
> system is not using benefits offered by the pcp lists when there is a
> single onlineable memory block in a zone. Correct this by always
> updating the pcp lists when memory block is onlined.
> 
> Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>

Makes sense to me.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/memory_hotplug.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index dcdf327..7f62d69 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -854,8 +854,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	node_states_set_node(nid, &arg);
>  	if (need_zonelists_rebuild)
>  		build_all_zonelists(NULL);
> -	else
> -		zone_pcp_update(zone);
> +	zone_pcp_update(zone);
>  
>  	init_per_zone_wmark_min();
>  
>