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

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Message-ID: <YL3QApMe/9R/xfLU@dhcp22.suse.cz>
Date:   Mon, 7 Jun 2021 09:51:30 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.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

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 The memory hot(un)plug documentation is outdated and incomplete.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

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Muchun Song <songmuchun@...edance.com>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: linux-doc@...r.kernel.org
> Signed-off-by: David Hildenbrand <david@...hat.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks a lot David!
-- 
Michal Hocko
SUSE Labs