On Mon, Aug 01, 2016 at 04:13:08PM +0300, Vladimir Davydov wrote: > Radix trees may be used not only for storing page cache pages, so > unconditionally accounting radix tree nodes to the current memory cgroup > is bad: if a radix tree node is used for storing data shared among > different cgroups we risk pinning dead memory cgroups forever. So let's > only account radix tree nodes if it was explicitly requested by passing > __GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account > page cache entries, so mark mapping->page_tree so.
Is this a theoretical fix, or did you actually run into problems? I wouldn't expect any other radix tree node consumer in the kernel to come anywhere close to the page cache, so I wonder why it matters. > @@ -351,6 +351,12 @@ static int __radix_tree_preload(gfp_t gfp_mask, int nr) > struct radix_tree_node *node; > int ret = -ENOMEM; > > + /* > + * Nodes preloaded by one cgroup can be be used by another cgroup, so > + * they should never be accounted to any particular memory cgroup. > + */ > + gfp_mask &= ~__GFP_ACCOUNT; But *all* page cache radix tree nodes are allocated from inside the preload code, since the tree insertions need mapping->tree_lock. So this would effectively disable accounting of the biggest radix tree consumer in the kernel, no?
