linux-kernel - Re: [RFC] mm/hotplug: Make get_nid_for_pfn() work with HAVE_ARCH_PFN

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Message-ID: <20190326122522.GO28406@dhcp22.suse.cz>
Date:   Tue, 26 Mar 2019 13:25:22 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        logang@...tatee.com, osalvador@...e.de, hannes@...xchg.org,
        akpm@...ux-foundation.org, richard.weiyang@...il.com,
        rientjes@...gle.com, zi.yan@...rutgers.edu
Subject: Re: [RFC] mm/hotplug: Make get_nid_for_pfn() work with
 HAVE_ARCH_PFN_VALID

On Tue 26-03-19 17:33:19, Anshuman Khandual wrote:
[...]
> I could get it working with the following re-order of memblock_[free|remove] and
> arch_remove_memory(). I did not observe any other adverse side affect because of
> this change. Does it look okay ?

Memblock should only work with physical memory ranges without touching
struct pages so this should be safe. But you should double check of
course.

> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1863,11 +1863,11 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
>  
>         /* remove memmap entry */
>         firmware_map_remove(start, start + size, "System RAM");
> +       arch_remove_memory(nid, start, size, NULL);
> +
>         memblock_free(start, size);
>         memblock_remove(start, size);
>  
> -       arch_remove_memory(nid, start, size, NULL);
> -
>         try_offline_node(nid);
>  
>         mem_hotplug_done();

-- 
Michal Hocko
SUSE Labs