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

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Date:   Fri, 11 Sep 2020 22:49:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        "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 ?



> Am 11.09.2020 um 22:09 schrieb Luck, Tony <tony.luck@...el.com>:
> 
> 
>> 
>> 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.
> 

Thanks a lot - so I‘m really spoiled by hot(un)plug capabilities in virtualized environments :D

> -Tony