From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-s390@vger.kernel.org, Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Philipp Rudo <prudo@linux.ibm.com>,
Kirill Smelkov <kirr@nexedi.com>,
Alexander Egorenkov <egorenar@linux.vnet.ibm.com>
Subject: Re: [PATCH RFC 1/2] s390/zcore: traverse resources instead of memblocks
Date: Wed, 10 Jun 2020 13:45:23 +0200 [thread overview]
Message-ID: <20200610114523.GA5943@osiris> (raw)
In-Reply-To: <20200417150151.17239-2-david@redhat.com>
On Fri, Apr 17, 2020 at 05:01:50PM +0200, David Hildenbrand wrote:
> The zcore memmap basically contains the first level of all system RAM from
> /proc/iomem. We want to disable CONFIG_ARCH_KEEP_MEMBLOCK (e.g., to not
> create memblocks for hotplugged/standby memory and save space), switch to
> traversing system ram resources instead. During early boot, we create
> resources for all early memblocks (including the crash kernel area). When
> adding standby memory, we currently create both, memblocks and resources.
>
> Note: As we don't have memory hotplug after boot (standby memory is added
> via sclp during boot), we don't have to worry about races.
>
> I am only able to test under KVM (where I hacked up zcore to still
> create the memmap file)
>
> root@vm0:~# cat /proc/iomem
> 00000000-2fffffff : System RAM
> 10424000-10ec6fff : Kernel code
> 10ec7000-1139a0e3 : Kernel data
> 1177a000-11850fff : Kernel bss
> 30000000-3fffffff : Crash kernel
>
> Result without this patch:
> root@vm0:~# cat /sys/kernel/debug/zcore/memmap
> 0000000000000000 0000000040000000
>
> Result with this patch:
> root@vm0:~# cat /sys/kernel/debug/zcore/memmap
> 0000000000000000 0000000030000000 0000000030000000 0000000010000000
>
> The difference is due to memblocks getting merged, resources (currently)
> not. So we might have some more entries, but they describe the same
> memory map.
>
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Cc: Philipp Rudo <prudo@linux.ibm.com>
> Cc: Kirill Smelkov <kirr@nexedi.com>
> Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/s390/char/zcore.c | 61 ++++++++++++++++++++++++++++++---------
> 1 file changed, 48 insertions(+), 13 deletions(-)
I'm having a hard time to find any code that ever made use of this
file. After all this was only meant for our zfcp dumper, but as far as
I can tell there was never code out there that read the memmap file.
So the pragmatic approach would be to just change its contents, or a
more progressive variant would be to remove the file completely.
But maybe I'm entirely wrong...
I'm leaving this up to Philipp and Alexander :)
next prev parent reply other threads:[~2020-06-10 11:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 15:01 [PATCH RFC 0/2] s390/mm: don't set ARCH_KEEP_MEMBLOCK David Hildenbrand
2020-04-17 15:01 ` [PATCH RFC 1/2] s390/zcore: traverse resources instead of memblocks David Hildenbrand
2020-06-10 11:45 ` Heiko Carstens [this message]
2020-06-19 12:47 ` Philipp Rudo
2020-06-19 12:49 ` David Hildenbrand
2020-04-17 15:01 ` [PATCH RFC 2/2] s390/mm: don't set ARCH_KEEP_MEMBLOCK David Hildenbrand
2020-06-26 16:32 ` Heiko Carstens
2020-06-29 12:44 ` Heiko Carstens
2020-06-29 13:02 ` David Hildenbrand
2020-04-29 14:55 ` [PATCH RFC 0/2] " David Hildenbrand
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