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

From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <osalvador@suse.de>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	linux-doc@vger.kernel.org
Subject: Re: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul
Date: Mon, 7 Jun 2021 10:08:59 +0200	[thread overview]
Message-ID: <14b018b0-aa19-7d00-2861-50d0e5e2bea8@redhat.com> (raw)
In-Reply-To: <YL3QApMe/9R/xfLU@dhcp22.suse.cz>

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 The memory hot(un)plug documentation is outdated and incomplete.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