linux-kernel - RE: Ways to deprecate /sys/devices/system/memory/memoryX/phys

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Date:   Fri, 11 Sep 2020 20:09:47 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     David Hildenbrand <david@...hat.com>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jan Höppner <hoeppner@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Ways to deprecate /sys/devices/system/memory/memoryX/phys_device
 ?

> How would it behave after hotplugging a single DIMM  - I assume a single page will only be mapped to that DIMM (otherwise a lot of stuff would habe to be moved around. Would the mapping change after a reboot - especially can a DIMM that could get hotunplugged before suddenly no longer be hotunplugged individually?


We don't currently have any platforms that would allow hot adding at the DIMM level.
The Brickland generation of E7 Xeon servers (Ivybridge, Haswell, Broadwell) allowed
for hot plugging a riser card that contained up to 12 DIMMs.

If you did add memory it would have to appear at the top of the system physical
address space. No interleave (unless you added more than one DIMM in a single
operation).  After a reboot the system would likely shuffle things around to and
interleave.

-Tony