linux-kernel - Re: [PATCH] kexec/powerpc: fix exporting memory limit

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Date:   Fri, 11 Mar 2022 16:26:14 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nikita Yushchenko <nyushchenko@....rtsoft.ru>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     yadviga@....rtsoft.ru, lugovskoy@....rtsoft.ru,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Paul Mackerras <paulus@...ba.org>,
        Anton Blanchard <anton@...ba.org>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] kexec/powerpc: fix exporting memory limit



Le 07/03/2014 à 05:38, Nikita Yushchenko a écrit :
>> On Thu, 2014-03-06 at 18:24 +0400, Nikita Yushchenko wrote:
>>> When preparing dump-capturing kernel, kexec userspace tool needs to
>>> know actual amount of memory used by the running kernel. This may
>>> differ from extire available DRAM for a couple of reasons. To address
>>> this issue, kdump kernel support code injects several attributes into
>>> device tree that are later captured by userspace kexec tool via /proc
>>> interface.
>>>
>>> One such attrubute is 'chosen/linux,memory_limit' that is used to pass
>>> memory limit of the running kernel.
>>>
>>> This was initialized using kernel's 'memory_limit' variable, that is
>>> set by early init code based on mem= kernel parameter and other
>>> reasons.
>>>
>>> But there are cases when memory_limit variable does not contain proper
>>> information. One such case is when !CONFIG_HIGHMEM kernel runs on
>>> system with memory large enough not to fit into lowmem.
>>
>> Why doesn't the !CONFIG_HIGHMEM code update memory_limit to reflect
>> reality.
> 
> I guess because memory_limit is used for ... well, memory limit, set by
> mem=. And for the rest memblock is used (and it *is* updated).
> 
> And code elsewhere does use memblock, see e.g. numa_enforce_memory_limit()
> in arch/powerpc/mm/numa.c
> 
> In MMU init (MMU_init() in arch/powerpc/mm/init_32.c -which is the point
> where final memory configuration is set) memblock, not memory_limit, is
> both used and updated.


We still have this patch as "New" in patchwork.

I don't know if it is relevant but directory structure has changed so if 
still needed this patch needs rebase.

Christophe