linux-kernel - Re: [PATCH 0/8] implement "memmap on memory" feature on s390

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Message-ID: <57762a6b-24c1-44a7-b1f3-4e73fe3b963d@redhat.com>
Date:   Fri, 17 Nov 2023 16:37:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sumanth Korikkar <sumanthk@...ux.ibm.com>
Cc:     linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/8] implement "memmap on memory" feature on s390

On 17.11.23 14:56, Sumanth Korikkar wrote:
> On Fri, Nov 17, 2023 at 12:08:31AM +0100, David Hildenbrand wrote:
>> On 14.11.23 19:02, Sumanth Korikkar wrote:
>>> Hi All,
>>>
>>> The patch series implements "memmap on memory" feature on s390 and
>>> provides the necessary fixes for it.
>>
>> Thinking about this, one thing that makes s390x different from all the other
>> architectures in this series is the altmap handling.
>>
>> I'm curious, why is that even required?
>>
>> A memmep that is not marked as online in the section should not be touched
>> by anybody (except memory onlining code :) ). And if we do, it's usually a
>> BUG because that memmap might contain garbage/be poisoned or completely
>> stale, so we might want to track that down and fix it in any case.
>>
>> So what speaks against just leaving add_memory() populate the memmap from
>> the altmap? Then, also the page tables for the memmap are already in place
>> when onlining memory.
>>
> 
> we do have page_init_poison() in sparse_add_section() which should be
> handled later then. not in add_pages()

Was that all, or did you stumble over other things?

-- 
Cheers,

David / dhildenb