From: Vladimir Davydov <[email protected]> commit 1f47b61fb4077936465dcde872a4e5cc4fe708da upstream.
An offline memory cgroup might have anonymous memory or shmem left charged to it and no swap. Since only swap entries pin the id of an offline cgroup, such a cgroup will have no id and so an attempt to swapout its anon/shmem will not store memory cgroup info in the swap cgroup map. As a result, memcg->swap or memcg->memsw will never get uncharged from it and any of its ascendants. Fix this by always charging swapout to the first ancestor cgroup that hasn't released its id yet. [[email protected]: add comment to mem_cgroup_swapout] [[email protected]: use WARN_ON_ONCE() in mem_cgroup_id_get_online()] Link: http://lkml.kernel.org/r/20160803123445.GJ13263@esperanza Fixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after many small jobs") Link: http://lkml.kernel.org/r/5336daa5c9a32e776067773d9da655d2dc126491.1470219853.git.vdavy...@virtuozzo.com Signed-off-by: Vladimir Davydov <[email protected]> Acked-by: Johannes Weiner <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: <[email protected]> [3.19+] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Michal Hocko <[email protected]> --- mm/memcontrol.c | 37 +++++++++++++++++++++++++++++++++---- 1 file changed, 33 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2c11422f0519..f5c74c8fcfcb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4141,6 +4141,24 @@ static void mem_cgroup_id_get(struct mem_cgroup *memcg) atomic_inc(&memcg->id.ref); } +static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) +{ + while (!atomic_inc_not_zero(&memcg->id.ref)) { + /* + * The root cgroup cannot be destroyed, so it's refcount must + * always be >= 1. + */ + if (WARN_ON_ONCE(memcg == root_mem_cgroup)) { + VM_BUG_ON(1); + break; + } + memcg = parent_mem_cgroup(memcg); + if (!memcg) + memcg = root_mem_cgroup; + } + return memcg; +} + static void mem_cgroup_id_put(struct mem_cgroup *memcg) { if (atomic_dec_and_test(&memcg->id.ref)) { @@ -5721,7 +5739,7 @@ subsys_initcall(mem_cgroup_init); */ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) { - struct mem_cgroup *memcg; + struct mem_cgroup *memcg, *swap_memcg; unsigned short oldid; VM_BUG_ON_PAGE(PageLRU(page), page); @@ -5736,16 +5754,27 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) if (!memcg) return; - mem_cgroup_id_get(memcg); - oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg)); + /* + * In case the memcg owning these pages has been offlined and doesn't + * have an ID allocated to it anymore, charge the closest online + * ancestor for the swap instead and transfer the memory+swap charge. + */ + swap_memcg = mem_cgroup_id_get_online(memcg); + oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg)); VM_BUG_ON_PAGE(oldid, page); - mem_cgroup_swap_statistics(memcg, true); + mem_cgroup_swap_statistics(swap_memcg, true); page->mem_cgroup = NULL; if (!mem_cgroup_is_root(memcg)) page_counter_uncharge(&memcg->memory, 1); + if (memcg != swap_memcg) { + if (!mem_cgroup_is_root(swap_memcg)) + page_counter_charge(&swap_memcg->memsw, 1); + page_counter_uncharge(&memcg->memsw, 1); + } + /* * Interrupts should be disabled here because the caller holds the * mapping->tree_lock lock which is taken with interrupts-off. It is -- 2.8.1
