From 100cc2b84c27c7b9189858922a62a22378523673 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 26 Jun 2014 10:42:39 +1000 Subject: [PATCH] mm: memcontrol: rewrite uncharge API fix 2 It's not entirely clear whether do_swap_account or PCG_MEMSW is the authoritative answer to whether a page is swap-accounted or not. This currently leads to the following memsw counter underflow when swap accounting is disabled: [ 2.753355] WARNING: CPU: 0 PID: 1 at kernel/res_counter.c:28 res_counter_uncharge_locked+0x48/0x74() [ 2.753355] CPU: 0 PID: 1 Comm: init Not tainted 3.16.0-rc1-00238-gddc5bfe #1 [ 2.753355] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 2.753355] 0000000000000000 ffff880012073c50 ffffffff81a23b9d ffff880012073c88 [ 2.753355] ffffffff810bc765 ffffffff8111fac8 0000000000001000 ffff88001200fa50 [ 2.753355] 0000000000000001 ffff88001200fa01 ffff880012073c98 ffffffff810bc84b [ 2.753355] Call Trace: [ 2.753355] [] dump_stack+0x19/0x1b [ 2.753355] [] warn_slowpath_common+0x73/0x8c [ 2.753355] [] ? res_counter_uncharge_locked+0x48/0x74 [ 2.753355] [] warn_slowpath_null+0x1a/0x1c [ 2.753355] [] res_counter_uncharge_locked+0x48/0x74 [ 2.753355] [] res_counter_uncharge_until+0x4e/0xa9 [ 2.753355] [] res_counter_uncharge+0x13/0x15 [ 2.753355] [] mem_cgroup_uncharge_end+0x73/0x8d [ 2.753355] [] release_pages+0x1f2/0x20d [ 2.753355] [] tlb_flush_mmu_free+0x28/0x43 [ 2.753355] [] tlb_flush_mmu+0x20/0x23 [ 2.753355] [] tlb_finish_mmu+0x14/0x39 [ 2.753355] [] unmap_region+0xcd/0xdf [ 2.753355] [] ? vma_gap_callbacks_propagate+0x18/0x33 [ 2.753355] [] do_munmap+0x252/0x2e0 [ 2.753355] [] vm_munmap+0x44/0x5c [ 2.753355] [] SyS_munmap+0x23/0x29 [ 2.753355] [] system_call_fastpath+0x16/0x1b [ 2.753355] ---[ end trace cfeb07101f6fbdfb ]--- Don't set PCG_MEMSW when swap accounting is disabled, so that uncharging only has to look at this per-page flag. mem_cgroup_swapout() could also fully rely on this flag, but as it can bail out before even looking up the page_cgroup, check do_swap_account as a performance optimization and only sanity test for PCG_MEMSW. Signed-off-by: Johannes Weiner Reported-by: Fengguang Wu Cc: Michal Hocko Tested-by: Jet Chen Signed-off-by: Andrew Morton --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 3e04ef4a223c..81cf1933119d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2740,7 +2740,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg, * have the page locked */ pc->mem_cgroup = memcg; - pc->flags = PCG_USED | PCG_MEM | PCG_MEMSW; + pc->flags = PCG_USED | PCG_MEM | (do_swap_account ? PCG_MEMSW : 0); if (lrucare) { if (was_on_lru) { @@ -6649,7 +6649,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage, return; VM_BUG_ON_PAGE(!(pc->flags & PCG_MEM), oldpage); - VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), oldpage); + VM_BUG_ON_PAGE(do_swap_account && !(pc->flags & PCG_MEMSW), oldpage); pc->flags &= ~(PCG_MEM | PCG_MEMSW); if (PageTransHuge(oldpage)) { -- 2.39.5