Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH v2 0/1] memory_hotplug: fix the panic when memory end is not
@ 2018-11-05 15:04 Mikhail Zaslonko
  2018-11-05 15:04 ` [PATCH v2 1/1] memory_hotplug: fix the panic when memory end is not on the section boundary Mikhail Zaslonko
  2018-11-05 18:35 ` [PATCH v2 0/1] memory_hotplug: fix the panic when memory end is not Michal Hocko
  0 siblings, 2 replies; 4+ messages in thread
From: Mikhail Zaslonko @ 2018-11-05 15:04 UTC (permalink / raw)
  To: akpm
  Cc: linux-kernel, linux-mm, mhocko, Pavel.Tatashin, schwidefsky,
	heiko.carstens, gerald.schaefer, zaslonko

This patch refers to the older thread:
https://marc.info/?t=153658306400001&r=1&w=2

I have tried to take the approaches suggested in the discussion like
simply ignoring unaligned memory to section memory much earlier or
initializing struct pages beyond the "end" but both had issues.

First I tried to ignore unaligned memory early by adjusting memory_end
value. But the thing is that kernel mem parameter parsing and memory_end
calculation take place in the architecture code and adjusting it afterwards
in common code might be too late in my view. Also with this approach we
might lose the memory up to the entire section(256Mb on s390) just because
of unfortunate alignment.

Another approach was to fix memmap_init() and initialize struct pages
beyond the end. Since struct pages are allocated section-wise we can try to
round the size parameter passed to the memmap_init() function up to the
section boundary thus forcing the mapping initialization for the entire
section. But then it leads to another VM_BUG_ON panic due to
zone_spans_pfn() sanity check triggered for the first page of each page
block from set_pageblock_migratetype() function:
 page dumped because: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn))
      Call Trace:
      ([<00000000003013f8>] set_pfnblock_flags_mask+0xe8/0x140)
       [<00000000003014aa>] set_pageblock_migratetype+0x5a/0x70
       [<0000000000bef706>] memmap_init_zone+0x25e/0x2e0
       [<00000000010fc3d8>] free_area_init_node+0x530/0x558
       [<00000000010fcf02>] free_area_init_nodes+0x81a/0x8f0
       [<00000000010e7fdc>] paging_init+0x124/0x130
       [<00000000010e4dfa>] setup_arch+0xbf2/0xcc8
       [<00000000010de9e6>] start_kernel+0x7e/0x588
       [<000000000010007c>] startup_continue+0x7c/0x300
      Last Breaking-Event-Address:
       [<00000000003013f8>] set_pfnblock_flags_mask+0xe8/0x1401
We might ignore this check for the struct pages beyond the "end" but I'm not
sure about further implications.
For now I suggest to stay with my original proposal fixing specific
functions for memory hotplug sysfs handlers.

Changes v1 -> v2:
* Expanded commit message to show both failing scenarious.
* Use 'pfn + i' instead of 'pfn' for zone_spans_pfn() check within
test_pages_in_a_zone() function thus taking CONFIG_HOLES_IN_ZONE into
consideration.

Mikhail Zaslonko (1):
  memory_hotplug: fix the panic when memory end is not on the section
    boundary

 mm/memory_hotplug.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

-- 
2.16.4

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, back to index

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-05 15:04 [PATCH v2 0/1] memory_hotplug: fix the panic when memory end is not Mikhail Zaslonko
2018-11-05 15:04 ` [PATCH v2 1/1] memory_hotplug: fix the panic when memory end is not on the section boundary Mikhail Zaslonko
2019-06-14 21:56   ` Sasha Levin
2018-11-05 18:35 ` [PATCH v2 0/1] memory_hotplug: fix the panic when memory end is not Michal Hocko

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org linux-mm@archiver.kernel.org
	public-inbox-index linux-mm


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox