linux-kernel - Re: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul

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Date:   Mon, 7 Jun 2021 10:08:59 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Muchun Song <songmuchun@...edance.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Jonathan Corbet <corbet@....net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul

On 07.06.21 09:51, Michal Hocko wrote:
> [Sorry this somehow slipped through cracks]
> 
> On Tue 25-05-21 12:26:04, David Hildenbrand wrote:
>> The memory hot(un)plug documentation is outdated and incomplete. Most of
>> the content dates back to 2007, so it's time for a major overhaul.
>>
>> Let's rewrite, reorganize and update most parts of the documentation. In
>> addition to memory hot(un)plug, also add some details regarding
>> ZONE_MOVABLE, with memory hotunplug being one of its main consumers.
>>
>> The style of the document is also properly fixed that e.g., "restview"
>> renders it cleanly now.
>>
>> In the future, we might add some more details about virt users like
>> virtio-mem, the XEN balloon, the Hyper-V balloon and ppc64 dlpar.
> 
> I haven't really checked the diff but rather looked at the final
> outcome. I have to say I like it a lot. Some places are going a bit too
> technical for an admin-guide but they are in minority (e.g. locking or
> altmap reference). If somebody feels strong then this could get into its
> own file but I wouldn't lose sleep over that.

I just realized that "Locking Internals" is still a duplicate with 
core-api/memory-hotplug.rst

I thought this (merge issue) was fixed long ago. I'll just remove it 
from this file, making sure core-api/memory-hotplug.rst is up-to-date

> 
> I would make one thing slightly more explicit though
> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> index c95f5c2b30dd..5b462aba89cc 100644
> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> @@ -568,6 +568,10 @@ Even with ZONE_MOVABLE, there are some corner cases where offlining a memory
>   Further, when running into out of memory situations while migrating pages, or
>   when still encountering permanently unmovable pages within ZONE_MOVABLE
>   (-> BUG), memory offlining will keep retrying until it eventually succeeds.
> +The offlining context can be terminated by a fatal signal. A timeout based
> +offlining can be easily implemented by
> +
> +        % timeout $TIMEOUT offline_block | failure_handling
>   
>   Locking Internals
>   =================
> 
> 
> In the future I would find some examples of a failure cases we have seen
> so far. E.g. offlining failure with dump_page example.


Thanks, I'll pick up your change and see if I can get rid of some 
low-level stuff. I'll address Mike's review shortly and resend.

-- 
Thanks,

David / dhildenb