From: Johannes Weiner hannes@cmpxchg.org Subject: mm: memcontrol: fix network errors from failing __GFP_ATOMIC charges

While upgrading from 4.16 to 5.2, we noticed these allocation errors in the log of the new kernel:

[ 8642.253395] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) [ 8642.269170] cache: tw_sock_TCPv6(960:helper-logs), object size: 232, buffer size: 240, default order: 1, min order: 0 [ 8642.293009] node 0: slabs: 5, objs: 170, free: 0

slab_out_of_memory+1 ___slab_alloc+969 __slab_alloc+14 kmem_cache_alloc+346 inet_twsk_alloc+60 tcp_time_wait+46 tcp_fin+206 tcp_data_queue+2034 tcp_rcv_state_process+784 tcp_v6_do_rcv+405 __release_sock+118 tcp_close+385 inet_release+46 __sock_release+55 sock_close+17 __fput+170 task_work_run+127 exit_to_usermode_loop+191 do_syscall_64+212 entry_SYSCALL_64_after_hwframe+68

accompanied by an increase in machines going completely radio silent under memory pressure.

One thing that changed since 4.16 is e699e2c6a654 ("net, mm: account sock objects to kmemcg"), which made these slab caches subject to cgroup memory accounting and control.

The problem with that is that cgroups, unlike the page allocator, do not maintain dedicated atomic reserves. As a cgroup's usage hovers at its limit, atomic allocations - such as done during network rx - can fail consistently for extended periods of time. The kernel is not able to operate under these conditions.

We don't want to revert the culprit patch, because it indeed tracks a potentially substantial amount of memory used by a cgroup.

We also don't want to implement dedicated atomic reserves for cgroups. There is no point in keeping a fixed margin of unused bytes in the cgroup's memory budget to accomodate a consumer that is impossible to predict - we'd be wasting memory and get into configuration headaches, not unlike what we have going with min_free_kbytes. We do this for physical mem because we have to, but cgroups are an accounting game.

Instead, account these privileged allocations to the cgroup, but let them bypass the configured limit if they have to. This way, we get the benefits of accounting the consumed memory and have it exert pressure on the rest of the cgroup, but like with the page allocator, we shift the burden of reclaimining on behalf of atomic allocations onto the regular allocations that can block.

Link: http://lkml.kernel.org/r/20191022233708.365764-1-hannes@cmpxchg.org Fixes: e699e2c6a654 ("net, mm: account sock objects to kmemcg") Signed-off-by: Johannes Weiner hannes@cmpxchg.org Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Suleiman Souhlal suleiman@google.com Cc: Michal Hocko mhocko@kernel.org Cc: stable@vger.kernel.org [4.18+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memcontrol.c | 9 +++++++++ 1 file changed, 9 insertions(+)

--- a/mm/memcontrol.c~mm-memcontrol-fix-network-errors-from-failing-__gfp_atomic-charges +++ a/mm/memcontrol.c @@ -2535,6 +2535,15 @@ retry: }

/* + * Memcg doesn't have a dedicated reserve for atomic + * allocations. But like the global atomic pool, we need to + * put the burden of reclaim on regular allocation requests + * and let these go through as privileged allocations. + */ + if (gfp_mask & __GFP_ATOMIC) + goto force; + + /* * Unlike in global OOM situations, memcg is not in a physical * memory shortage. Allow dying and OOM-killed tasks to * bypass the last charges so that they can exit quickly and _