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

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Date:   Mon, 14 Aug 2023 14:45:11 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     "Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:     "david@...hat.com" <david@...hat.com>,
        "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

"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.

--
Best Regards,
Huang, Ying