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Subject[RFC] memory hotremove patch take 2 [00/10]


I rebased and debugged Kame-san's memory hot-remove patches.
This work is not finished yet. (Some pages keep un-removable status)
But, I would like to show current progress of it, because it has
been a long time since previous post, and some bugs are fixed.

If you have concern, please check this. Any comments are welcome.



These patches are for memory hot-remove.

How to use
- kernelcore=xx[GMK] must be specified at boottime option to create
- After bootup, execute following.
# echo "offline" > /sys/devices/system/memory/memoryX/status

Change log from previous version.
- Rebase to 2.6.21-mm1.
- Old original ZONE_MOVABLE code is removed. Mel-san's ZONE_REMOVABLE
for anti-fragmentation is used.
- Fix wrong return code check of isolate_lru_page()
- Page is isolated ASAP, which was source of page migration when
memory-hotremove. In old code, it uses just put_page(),
and we expected that migrated source page is catched in
__free_one_page() as isolated page. But, it is spooled in
per_cpu_page and used soon for next destination page of migration.
This was cause of eternal loop in offline_pages().
- There is a page which is not mapped but added to swapcache in
swap-in code. It was cause of panic in try_to_unmap(). fixed it.
- end_pfn is rounded up at memmap_init. If there is a small hole on
end of section. These page is not initialized.

- There are some pages which are un-removable page on memory stress
condition. (These pages are set PG_swapcache or PG_mappedtodisk
without connecting to lru.)
- Should make i386/x86-64/powerpc interface code. But not yet
(really sorry :-( ).
- If bootmem parameter or efi's memory map is stored by efi, memory
can't be removed even if it is in removable zone.
- node hotplug support. (this may needs some amount of patches.)
- test under heavy work load and more careful race check.
- Fix where we should allocate migration target page from.
- Hmmmm.... And so on.

[1] counters patch -- per-zone counter for ZONE_MOVABLE

==page isolation==
[2] page isolation patch ..... basic defintions of page isolation.
[3] drain_all_zone_pages patch ..... drain all cpus' pcp pages.
[4] isolate freed page patch ..... isolate pages in free_area[]

==memory unplug==
offline a section of pages. isolate specified section and migrate
content of used pages to out of section. (Because free pages in a
section is isolated, it never be returned by alloc_pages())
This patch doesn't care where we should allocate migration new pages from.
[5] memory unplug core patch --- maybe need more work.
[6] interface patch --- "offline" interface support

==migration nocontext==
Fix race condition of page migration without process context
(not taking mm->sem). This patch delayes kmem_cache_free() of
anon_vma until migration ends.
[7] migration nocontext patch --- support page migration without
acquiring mm->sem. need careful debug...

==other fixes==
[8] round up end_pfn at memmap_init
[9] page isolation ASAP when memory-hotremove case.
[10] fix swapping-in page panic.

Yasunori Goto

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