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Message-ID: <0ea4728a-8601-bf75-1921-bcde0818aac3@redhat.com>
Date:   Fri, 16 Jun 2023 09:46:59 +0200
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Subject: Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the
 memmap_on_memory param
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To:     Vishal Verma <vishal.l.verma@intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>
Cc:     linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, nvdimm@lists.linux.dev,
        linux-cxl@vger.kernel.org, Huang Ying <ying.huang@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
References: <20230613-vv-kmem_memmap-v1-0-f6de9c6af2c6@intel.com>
 <20230613-vv-kmem_memmap-v1-1-f6de9c6af2c6@intel.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230613-vv-kmem_memmap-v1-1-f6de9c6af2c6@intel.com>
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On 16.06.23 00:00, Vishal Verma wrote:
> For memory hotplug to consider MHP_MEMMAP_ON_MEMORY behavior, the
> 'memmap_on_memory' module parameter was a hard requirement.
> 
> In preparation for the dax/kmem driver to use memmap_on_memory
> semantics, arrange for the module parameter check to be bypassed via the
> appropriate mhp_flag.
> 
> Recall that the kmem driver could contribute huge amounts of hotplugged
> memory originating from special purposes devices such as CXL memory
> expanders. In some cases memmap_on_memory may be the /only/ way this new
> memory can be hotplugged. Hence it makes sense for kmem to have a way to
> force memmap_on_memory without depending on a module param, if all the
> other conditions for it are met.

Just let the admin configure it. After all, an admin is involved in 
configuring the dax/kmem device to begin with. If add_memory() fails you 
could give a useful hint to the admin.

-- 
Cheers,

David / dhildenb