linux-kernel - Re: [PATCH 3/3] mm: use vmem_altmap code without CONFIG_ZONE

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Date:   Mon, 20 Nov 2023 10:01:13 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: use vmem_altmap code without CONFIG_ZONE_DEVICE

On 20.11.23 08:23, Sumanth Korikkar wrote:
> vmem_altmap_free() and vmem_altmap_offset() could be utlized without
> CONFIG_ZONE_DEVICE enabled. For example,
> mm/memory_hotplug.c:__add_pages() relies on that.  The altmap is no
> longer restricted to ZONE_DEVICE handling, but instead depends on
> CONFIG_SPARSEMEM_VMEMMAP.
> 
> When CONFIG_SPARSEMEM_VMEMMAP is disabled, these functions are defined
> as inline stubs, ensuring compatibility with configurations that do not
> use sparsemem vmemmap. Without it, lkp reported the following:
> 
> ld: arch/x86/mm/init_64.o: in function `remove_pagetable':
> init_64.c:(.meminit.text+0xfc7): undefined reference to
> `vmem_altmap_free'
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202311180545.VeyRXEDq-lkp@intel.com/
> Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---


[...]

>   
> +unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
> +{
> +	/* number of pfns from base where pfn_to_page() is valid */
> +	if (altmap)
> +		return altmap->reserve + altmap->free;
> +	return 0;
> +}
> +
> +void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns)
> +{
> +	altmap->alloc -= nr_pfns;
> +}

What speaks against just moving them to the header instead? They surely 
are tiny ...

-- 
Cheers,

David / dhildenb