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From: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
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	Catalin Marinas <catalin.marinas@arm.com>,
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	Masahiro Yamada <yamada.masahiro@socionext.com>,
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	Wei Yang <richard.weiyang@gmail.com>, Qian Cai <cai@lca.pw>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Logan Gunthorpe <logang@deltatee.com>,
	Ira Weiny <ira.weiny@intel.com>
Subject: Re: [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining memory
Date: Sat, 30 Nov 2019 15:21:59 -0800
Message-ID: <20191130152159.258fa331542fc693e24723eb@linux-foundation.org> (raw)
In-Reply-To: <f75caf18-ff5f-8a29-7069-8ce783389644@redhat.com>

On Sun, 27 Oct 2019 23:45:52 +0100 David Hildenbrand <david@redhat.com> wrote:

> I think I just found an issue with try_offline_node(). 
> try_offline_node() is pretty much broken already (touches garbage 
> memmaps and will not considers mixed NIDs within sections), however, 
> relies on the node span to look for memory sections to probe. So it 
> seems to rely on the nodes getting shrunk when removing memory, not when 
> offlining.
> 
> As we shrink the node span when offlining now and not when removing, 
> this can go wrong once we offline the last memory block of the node and 
> offline the last CPU. We could still have memory around that we could 
> re-online, however, the node would already be offline. Unlikely, but 
> possible.
> 
> Note that the same is also broken without this patch in case memory is 
> never onlined. The "pfn_to_nid(pfn) != nid" can easily succeed on the 
> garbage memmap, resulting in  no memory being detected as belonging to 
> the node. Also, resize_pgdat_range() is called when onlining memory, not 
> when adding it. :/ Oh this is so broken :)
> 
> The right fix is probably to walk over all memory blocks that could 
> exist and test if they belong to the nid (if offline, check the 
> block->nid, if online check all pageblocks). A fix we can then move in 
> front of this patch.
> 
> Will look into this this week.

And this series shows almost no sign of having been reviewed.  I'll hold
it over for 5.6.



  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-06  8:56 [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages() David Hildenbrand
2019-10-06 19:58   ` Damian Tometzki
2019-10-06 20:13     ` David Hildenbrand
2019-10-14  9:05   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 02/10] mm/memmap_init: Update variable name in memmap_init_zone David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 03/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_pgdat_span() David Hildenbrand
2019-10-14  9:31   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span() David Hildenbrand
2019-10-14  9:32   ` David Hildenbrand
2019-10-14 19:17     ` Andrew Morton
2019-11-19 14:16       ` David Hildenbrand
2019-11-19 20:44         ` Andrew Morton
2019-10-06  8:56 ` [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining memory David Hildenbrand
2019-10-14  9:39   ` David Hildenbrand
2019-10-14 19:16     ` Andrew Morton
2019-10-27 22:45   ` David Hildenbrand
2019-11-30 23:21     ` Andrew Morton [this message]
2019-11-30 23:43       ` David Hildenbrand
2019-12-18 17:08       ` David Hildenbrand
2019-12-18 20:16         ` Andrew Morton
2019-12-03 15:10   ` Oscar Salvador
2019-12-03 15:27     ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone() David Hildenbrand
2019-10-16 14:01   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span() David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 09/10] mm/memory_hotplug: Drop local variables " David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages() David Hildenbrand
2019-12-02  9:09 ` [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-12-03 13:36   ` Oscar Salvador

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