linux-kernel - Re: [RFC 3/5] mm, page_alloc(): remove setup

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Message-ID: <2c38b1f8-4e60-39f8-66c7-c0bbdb9df3cc@suse.cz>
Date:   Fri, 18 Sep 2020 11:37:47 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC 3/5] mm, page_alloc(): remove setup_pageset()

On 9/10/20 11:23 AM, Oscar Salvador wrote:
> On Mon, Sep 07, 2020 at 06:36:26PM +0200, Vlastimil Babka wrote:
>> We initialize boot-time pagesets with setup_pageset(), which sets high and
>> batch values that effectively disable pcplists.
>> 
>> We can remove this wrapper if we just set these values for all pagesets in
>> pageset_init(). Non-boot pagesets then subsequently update them to specific
>> values.
>> 
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Reviewed-by: Oscar Salvador <osalvador@...e.de>

Thanks!

> Just one question below:
> 
>> -static void setup_pageset(struct per_cpu_pageset *p)
>> -{
>> -	pageset_init(p);
>> -	pageset_update(&p->pcp, 0, 1);
>> +	/*
>> +	 * Set batch and high values safe for a boot pageset. Proper pageset's
>> +	 * initialization will update them.
>> +	 */
>> +	pcp->high = 0;
>> +	pcp->batch  = 1;
> 
> pageset_update was manipulating these values with barriers in between.
> I guess we do not care here because we are not really updating but
> initializing them, right?

Sure. We just initialized all the list heads, so there can be no concurrent
access at this point. But I'll mention it in the comment.