linux-kernel - Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on

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Date:   Mon, 14 Aug 2023 09:20:11 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:     "Jiang, Dave" <dave.jiang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "aneesh.kumar@...ux.ibm.com" <aneesh.kumar@...ux.ibm.com>,
        "jmoyer@...hat.com" <jmoyer@...hat.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Bernhard Walle <bernhard.walle@....de>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory requests
 across memblocks

On 14.08.23 08:45, Huang, Ying wrote:
> "Verma, Vishal L" <vishal.l.verma@...el.com> writes:
> 
>> On Mon, 2023-07-24 at 13:54 +0800, Huang, Ying wrote:
>>> Vishal Verma <vishal.l.verma@...el.com> writes:
>>>
>>>>
>>>> @@ -2035,12 +2056,38 @@ void try_offline_node(int nid)
>>>>   }
>>>>   EXPORT_SYMBOL(try_offline_node);
>>>>
>>>> -static int __ref try_remove_memory(u64 start, u64 size)
>>>> +static void __ref __try_remove_memory(int nid, u64 start, u64 size,
>>>> +                                    struct vmem_altmap *altmap)
>>>>   {
>>>> -       struct vmem_altmap mhp_altmap = {};
>>>> -       struct vmem_altmap *altmap = NULL;
>>>> -       unsigned long nr_vmemmap_pages;
>>>> -       int rc = 0, nid = NUMA_NO_NODE;
>>>> +       /* remove memmap entry */
>>>> +       firmware_map_remove(start, start + size, "System RAM");
>>>
>>> If mhp_supports_memmap_on_memory(), we will call
>>> firmware_map_add_hotplug() for whole range.  But here we may call
>>> firmware_map_remove() for part of range.  Is it OK?
>>>
>>
>> Good point, this is a discrepancy in the add vs remove path. Can the
>> firmware memmap entries be moved up a bit in the add path, and is it
>> okay to create these for each memblock? Or should these be for the
>> whole range? I'm not familiar with the implications. (I've left it as
>> is for v3 for now, but depending on the direction I can update in a
>> future rev).
> 
> Cced more firmware map developers and maintainers.
> 
> Per my understanding, we should create one firmware memmap entry for
> each memblock.

Ideally we should create it for the whole range, ti limit the ranges. 
But it really only matters for DIMMs; for dax/kmem, we'll not create any 
firmware entries.

-- 
Cheers,

David / dhildenb