Hi, I verified the log files and see no prior oom killer invocation. Unfortunately the machine has been rebooted since. Next time it happens, I will also look in dmesg.
Thanks, David Arendt Michal Hocko – Wed., 14. December 2016 11:31 > Btw. the stall should be preceded by the OOM killer invocation. Could > you share the OOM report please. I am asking because such an OOM killer > would be clearly pre-mature as per your meminfo. I am trying to change > that code and seeing your numbers might help me. > > Thanks! > > On Wed 14-12-16 11:17:43, Michal Hocko wrote: > > On Tue 13-12-16 18:11:01, David Arendt wrote: > > > Hi, > > > > > > I receive the following page allocation stall while copying lots of > > > large files from one btrfs hdd to another. > > > > > > Dec 13 13:04:29 server kernel: kworker/u16:8: page allocation stalls for > > > 12260ms, order:0, mode:0x2400840(GFP_NOFS|__GFP_NOFAIL) > > > Dec 13 13:04:29 server kernel: CPU: 0 PID: 24959 Comm: kworker/u16:8 > > > Tainted: P O 4.9.0 #1 > > [...] > > > Dec 13 13:04:29 server kernel: Call Trace: > > > Dec 13 13:04:29 server kernel: [<ffffffff813f3a59>] ? > > > dump_stack+0x46/0x5d > > > Dec 13 13:04:29 server kernel: [<ffffffff81114fc1>] ? > > > warn_alloc+0x111/0x130 > > > Dec 13 13:04:33 server kernel: [<ffffffff81115c38>] ? > > > __alloc_pages_nodemask+0xbe8/0xd30 > > > Dec 13 13:04:33 server kernel: [<ffffffff8110de74>] ? > > > pagecache_get_page+0xe4/0x230 > > > Dec 13 13:04:33 server kernel: [<ffffffff81323a8b>] ? > > > alloc_extent_buffer+0x10b/0x400 > > > Dec 13 13:04:33 server kernel: [<ffffffff812ef8c5>] ? > > > btrfs_alloc_tree_block+0x125/0x560 > > > > OK, so this is > > find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL) > > > > The main question is whether this really needs to be NOFS request... > > > > > Dec 13 13:04:33 server kernel: [<ffffffff8132442f>] ? > > > read_extent_buffer_pages+0x21f/0x280 > > > Dec 13 13:04:33 server kernel: [<ffffffff812d81f1>] ? > > > __btrfs_cow_block+0x141/0x580 > > > Dec 13 13:04:33 server kernel: [<ffffffff812d87b0>] ? > > > btrfs_cow_block+0x100/0x150 > > > Dec 13 13:04:33 server kernel: [<ffffffff812dc1d9>] ? > > > btrfs_search_slot+0x1e9/0x9c0 > > > Dec 13 13:04:33 server kernel: [<ffffffff8131ead2>] ? > > > __set_extent_bit+0x512/0x550 > > > Dec 13 13:04:33 server kernel: [<ffffffff812e1ab5>] ? > > > lookup_inline_extent_backref+0xf5/0x5e0 > > > Dec 13 13:04:34 server kernel: [<ffffffff8131f0a4>] ? > > > set_extent_bit+0x24/0x30 > > > Dec 13 13:04:34 server kernel: [<ffffffff812e4334>] ? > > > update_block_group.isra.34+0x114/0x380 > > > Dec 13 13:04:34 server kernel: [<ffffffff812e4694>] ? > > > __btrfs_free_extent.isra.35+0xf4/0xd20 > > > Dec 13 13:04:34 server kernel: [<ffffffff8134d561>] ? > > > btrfs_merge_delayed_refs+0x61/0x5d0 > > > Dec 13 13:04:34 server kernel: [<ffffffff812e8bd2>] ? > > > __btrfs_run_delayed_refs+0x902/0x10a0 > > > Dec 13 13:04:34 server kernel: [<ffffffff812ec0f0>] ? > > > btrfs_run_delayed_refs+0x90/0x2a0 > > > Dec 13 13:04:34 server kernel: [<ffffffff812ec384>] ? > > > delayed_ref_async_start+0x84/0xa0 > > > > What would cause the reclaim recursion? > > > > > Dec 13 13:04:34 server kernel: Mem-Info: > > > Dec 13 13:04:34 server kernel: active_anon:20 inactive_anon:34 > > > isolated_anon:0\x0a active_file:7370032 inactive_file:450105 > > > isolated_file:320\x0a unevictable:0 dirty:522748 writeback:189 > > > unstable:0\x0a slab_reclaimable:178255 slab_unreclaimable:124617\x0a > > > mapped:4236 shmem:0 pagetables:1163 bounce:0\x0a free:38224 free_pcp:241 > > > free_cma:0 > > > > This speaks for itself. There is a lot of dirty data, basically no > > anonymous memory and GFP_NOFS cannot do much to reclaim obviously. This > > is either a configuraion bug as somebody noted down the thread (setting > > the dirty_ratio) or suboptimality of the btrfs code which might request > > NOFS even though it is not strictly necessary. This would be more for > > btrfs developers. > > -- > > Michal Hocko > > SUSE Labs > > -- > Michal Hocko > SUSE Labs
