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Message-ID: <20230622143753.00000282@Huawei.com>
Date: Thu, 22 Jun 2023 14:37:53 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: David Hildenbrand <david@...hat.com>
CC: Vishal Verma <vishal.l.verma@...el.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <lenb@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Oscar Salvador <osalvador@...e.de>,
"Dan Williams" <dan.j.williams@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>, <nvdimm@...ts.linux.dev>,
<linux-cxl@...r.kernel.org>, Huang Ying <ying.huang@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the
memmap_on_memory param
On Fri, 16 Jun 2023 09:46:59 +0200
David Hildenbrand <david@...hat.com> wrote:
> 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.
>
Agreed. If it were just the default then fine, but making it the only option
limits admin choices.
Jonathan
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