From: "Oliver O'Halloran" <oohall@gmail.com>
To: Leonardo Bras <leonardo@linux.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Thomas Gleixner <tglx@linutronix.de>,
Nathan Fontenot <nfont@linux.vnet.ibm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Allison Randal <allison@lohutok.net>,
Bharata B Rao <bharata@linux.ibm.com>,
Claudio Carvalho <cclaudio@linux.ibm.com>,
Hari Bathini <hbathini@linux.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/1] powerpc/kernel: Enables memory hot-remove after reboot on pseries guests
Date: Fri, 3 Apr 2020 09:46:44 +1100 [thread overview]
Message-ID: <CAOSf1CEihBDDRny5S_7TA5Cqbdgsh6zN=kdq83OSgaLbRphtrg@mail.gmail.com> (raw)
In-Reply-To: <20200402195156.626430-1-leonardo@linux.ibm.com>
On Fri, Apr 3, 2020 at 6:55 AM Leonardo Bras <leonardo@linux.ibm.com> wrote:
>
> While providing guests, it's desirable to resize it's memory on demand.
>
> By now, it's possible to do so by creating a guest with a small base
> memory, hot-plugging all the rest, and using 'movable_node' kernel
> command-line parameter, which puts all hot-plugged memory in
> ZONE_MOVABLE, allowing it to be removed whenever needed.
>
> But there is an issue regarding guest reboot:
> If memory is hot-plugged, and then the guest is rebooted, all hot-plugged
> memory goes to ZONE_NORMAL, which offers no guaranteed hot-removal.
> It usually prevents this memory to be hot-removed from the guest.
>
> It's possible to use device-tree information to fix that behavior, as
> it stores flags for LMB ranges on ibm,dynamic-memory-vN.
> It involves marking each memblock with the correct flags as hotpluggable
> memory, which mm/memblock.c puts in ZONE_MOVABLE during boot if
> 'movable_node' is passed.
I don't really understand why the flag is needed at all. According to
PAPR any memory provided by dynamic reconfiguration can be hot-removed
so why aren't we treating all DR memory as hot removable? The only
memory guaranteed to be there 100% of the time is what's in the
/memory@0 node since that's supposed to cover the real mode area.
next prev parent reply other threads:[~2020-04-02 22:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-02 19:51 [PATCH v3 1/1] powerpc/kernel: Enables memory hot-remove after reboot on pseries guests Leonardo Bras
2020-04-02 22:46 ` Oliver O'Halloran [this message]
2020-04-02 23:06 ` Leonardo Bras
2020-04-02 23:31 ` Oliver O'Halloran
2020-04-02 23:41 ` Leonardo Bras
2020-04-03 14:38 ` Bharata B Rao
2020-04-06 15:41 ` Leonardo Bras
2020-04-07 4:00 ` Bharata B Rao
2020-04-07 16:32 ` Leonardo Bras
2020-06-09 5:29 ` Michael Ellerman
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