path: root/mm/memory_hotplug.c
diff options
authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-12-14 17:59:33 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-15 08:53:20 -0800
commit62b61f611eb5e20f7e9f8619bfd03bdfe8af6348 (patch)
tree9f06fff7eb6530fbe90b4d998b91071133f6af25 /mm/memory_hotplug.c
parente9995ef978a7d5296fe04a9a2c5ca6e66d8bb4e5 (diff)
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets into trouble: not surprising, since we're using the ksm page lock to lock operations on its stable_node, but page migration switches the page whose lock is to be used for that. Another layer of locking would fix it, but do we need that yet? Do we actually need page migration of ksm pages? Yes, memory hotremove needs to offline sections of memory: and since we stopped allocating ksm pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE candidates for migration. But KSM is currently unconscious of NUMA issues, happily merging pages from different NUMA nodes: at present the rule must be, not to use MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of ksm pages does not make sense yet. So, to complete support for ksm swapping we need to make hotremove safe. ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages are freed before migration reaches them, stable_nodes may be left still pointing to struct pages which have been removed from the system: the stable_node needs to identify a page by pfn rather than page pointer, then it can safely prune them when MEM_OFFLINE. And make NUMA migration skip PageKsm pages where it skips PageReserved. But it's only when we reach unmap_and_move() that the page lock is taken and we can be sure that raised pagecount has prevented a PageAnon from being upgraded: so add offlining arg to migrate_pages(), to migrate ksm page when offlining (has sufficient locking) but reject it otherwise. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Izik Eidus <ieidus@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Chris Wright <chrisw@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory_hotplug.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index bc5a08138f1..67e941d7882 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -698,7 +698,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
if (list_empty(&source))
goto out;
/* this function returns # of failed pages */
- ret = migrate_pages(&source, hotremove_migrate_alloc, 0);
+ ret = migrate_pages(&source, hotremove_migrate_alloc, 0, 1);
return ret;