On Fri 06-01-17 09:13:23, Mike Galbraith wrote:
> radix-tree: Partially disable memcg accounting in radix_tree_node_alloc()
>
> Having no preload, which turns accounting off for non-rt kernels, trying to
> allocate coming from shmem_fault() when memcg is full sends us scurrying off
> to pagefault_out_of_memory(), with dramatic (usually terminal) consequences.
> LTP's madvise06 testcase triggers this quite well, and per gitk, the below
> was the beginning of RT memcg woes.
>
> 58e698af4c63 radix-tree: account radix_tree_node to memory cgroup
>
> Turn memcg accounting off for RT in the problematic path.
I am really wondering why this is RT specific and the non RT kernels
doesn't have any problem.
> Signed-off-by: Mike Galbraith <efault@xxxxxx>
> Cc: stable-rt@xxxxxxxxxxxxxxx # +v4.6-rt
> ---
> lib/radix-tree.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -303,6 +303,13 @@ radix_tree_node_alloc(struct radix_tree_
> if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
> struct radix_tree_preload *rtp;
>
> +#if defined(CONFIG_PREEMPT_RT_FULL) && defined(CONFIG_MEMCG)
> + /*
> + * Arriving here from shmem_fault() and meeting a full memcg
> + * will send us to pagefault_out_of_memory(), and a dead box.
> + */
> + gfp_mask &= ~__GFP_ACCOUNT;
> +#endif
> /*
> * Even if the caller has preloaded, try to allocate from the
> * cache first for the new node to get accounted to the memory
--
Michal Hocko
SUSE Labs
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