linux-kernel - Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range

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Message-ID: <YF2hZ5Q27yb6jC7w@localhost.localdomain>
Date:   Fri, 26 Mar 2021 09:55:03 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...e.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added
 memory range

On Fri, Mar 26, 2021 at 09:35:03AM +0100, Michal Hocko wrote:
> No problem there. I will not insist on my approach unless I can convince
> you that it is a better solution. It seems I have failed and I can live
> with that.

Well, I am glad we got to discuss it at least.

> > +static int memory_block_online(unsigned long start_pfn, unsigned long nr_pages,
> > +			       unsigned long nr_vmemmap_pages, int online_type,
> > +			       int nid)
> > +{
> > +	int ret;
> > +	/*
> > +	 * Despite vmemmap pages having a different lifecycle than the pages
> > +	 * they describe, initialiating and accounting vmemmap pages at the
> > +	 * online/offline stage eases things a lot.
> 
> This requires quite some explaining.

Definitely, I will expand on that and provide some context.

 
> Yes this is much better! Just a minor suggestion would be to push
> memory_block all the way to memory_block_online (it oline a memory
> block). I would also slightly prefer to provide 2 helpers that would make
> it clear that this is to reserve/cleanup the vmemamp space (defined in
> the memory_hotplug proper).

Glad to hear that!
By pushing memory_block all the way to memory_block_{online,offline}, you
mean passing the memblock struct together with nr_vmemmap_pages,
only_type and nid to memory_block_{offline,online}, and derive in there
the start_pfn and nr_pages?

Wrt. to the two helpers, I agree with you.
Actually, I would find quite disturbing to deal with zones in that code
domain.
I will add two proper helpers in memory_hotplug to deal with vmemmap.

If it comes out the way I envision, it could end up quite clean, and much
less disturbing.

Thanks Michal

-- 
Oscar Salvador
SUSE L3