Messages in this thread Patch in this message | | | Subject | [PATCH 3/3] mm: strictly require elevated page refcount in isolate_lru_page() | From | Konstantin Khlebnikov <> | Date | Thu, 21 Apr 2011 17:12:42 +0400 |
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isolate_lru_page() must be called only with stable reference to the page, this is what is written in the comment above it, this is reasonable.
current isolate_lru_page() users and its page extra reference sources:
mm/huge_memory.c __collapse_huge_page_isolate() - reference from pte
mm/memcontrol.c mem_cgroup_move_parent() - get_page_unless_zero() mem_cgroup_move_charge_pte_range() - reference from pte
mm/memory-failure.c soft_offline_page() - fixed, reference from get_any_page() delete_from_lru_cache() - reference from caller or get_page_unless_zero() [seems like there bug, because __memory_failure() can call page_action() for hpages tail, but it is ok for isolate_lru_page(), tail getted and not in lru]
mm/memory_hotplug.c do_migrate_range() - fixed, get_page_unless_zero()
mm/mempolicy.c migrate_page_add() - reference from pte
mm/migrate.c do_move_page_to_node_array() - reference from follow_page()
mlock.c - various external references
mm/vmscan.c putback_lru_page() - reference from isolate_lru_page()
It seems that all isolate_lru_page() users are ready now for this restriction. So, let's replace redundant get_page_unless_zero() with get_page() and add page initial reference count check with VM_BUG_ON()
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org> --- mm/vmscan.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index f6b435c..0175f39 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1201,13 +1201,16 @@ int isolate_lru_page(struct page *page) { int ret = -EBUSY; + VM_BUG_ON(!page_count(page)); + if (PageLRU(page)) { struct zone *zone = page_zone(page); spin_lock_irq(&zone->lru_lock); - if (PageLRU(page) && get_page_unless_zero(page)) { + if (PageLRU(page)) { int lru = page_lru(page); ret = 0; + get_page(page); ClearPageLRU(page); del_page_from_lru_list(zone, page, lru);
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