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

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Date:   Fri, 11 Sep 2020 21:56:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     "Hansen, Dave" <dave.hansen@...el.com>,
        David Hildenbrand <david@...hat.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 21:36 schrieb Luck, Tony <tony.luck@...el.com>:
> 
> 
>> 
>> It's actually really hard to map a DIMM to a physical address.
>> Interleaving can mean that one page actually spans a bunch of DIMMs.
> 
> Heh! If NUMA mode is turned off your single page may have cache lines
> from *every* DIMM in the system. Even with NUMA turned on the page
> will have cache lines from every DIMM on the socket.
> 

Thanks Dave and Tony, that‘s valuable information!

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?

> -Tony