[PATCH 2/4] mm/slub: Use mem_node to allocate a new slab

[Vlastimil Babka]

On 3/17/20 2:17 PM, Srikar Dronamraju wrote:
> Currently while allocating a slab for a offline node, we use its
> associated node_numa_mem to search for a partial slab. If we don't find
> a partial slab, we try allocating a slab from the offline node using
> __alloc_pages_node. However this is bound to fail.
> 
> NIP [c00000000039a300] __alloc_pages_nodemask+0x130/0x3b0
> LR [c00000000039a3c4] __alloc_pages_nodemask+0x1f4/0x3b0
> Call Trace:
> [c0000008b36837f0] [c00000000039a3b4] __alloc_pages_nodemask+0x1e4/0x3b0 (unreliable)
> [c0000008b3683870] [c0000000003d1ff8] new_slab+0x128/0xcf0
> [c0000008b3683950] [c0000000003d6060] ___slab_alloc+0x410/0x820
> [c0000008b3683a40] [c0000000003d64a4] __slab_alloc+0x34/0x60
> [c0000008b3683a70] [c0000000003d78b0] __kmalloc_node+0x110/0x490
> [c0000008b3683af0] [c000000000343a08] kvmalloc_node+0x58/0x110
> [c0000008b3683b30] [c0000000003ffd44] mem_cgroup_css_online+0x104/0x270
> [c0000008b3683b90] [c000000000234e08] online_css+0x48/0xd0
> [c0000008b3683bc0] [c00000000023dedc] cgroup_apply_control_enable+0x2ec/0x4d0
> [c0000008b3683ca0] [c0000000002416f8] cgroup_mkdir+0x228/0x5f0
> [c0000008b3683d10] [c000000000520360] kernfs_iop_mkdir+0x90/0xf0
> [c0000008b3683d50] [c00000000043e400] vfs_mkdir+0x110/0x230
> [c0000008b3683da0] [c000000000441ee0] do_mkdirat+0xb0/0x1a0
> [c0000008b3683e20] [c00000000000b278] system_call+0x5c/0x68
> 
> Mitigate this by allocating the new slab from the node_numa_mem.

Are you sure this is really needed and the other 3 patches are not enough for
the current SLUB code to work as needed? It seems you are changing the semantics
here...

> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1970,14 +1970,8 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
>  		struct kmem_cache_cpu *c)
>  {
>  	void *object;
> -	int searchnode = node;
>  
> -	if (node == NUMA_NO_NODE)
> -		searchnode = numa_mem_id();
> -	else if (!node_present_pages(node))
> -		searchnode = node_to_mem_node(node);
> -
> -	object = get_partial_node(s, get_node(s, searchnode), c, flags);
> +	object = get_partial_node(s, get_node(s, node), c, flags);
>  	if (object || node != NUMA_NO_NODE)>  		return object;
>
>       return get_any_partial(s, flags, c);

I.e. here in this if(), now node will never equal NUMA_NO_NODE (thanks to the
hunk below), thus the get_any_partial() call becomes dead code?

> @@ -2470,6 +2464,11 @@ static inline void *new_slab_objects(struct kmem_cache *s, gfp_t flags,
>  
>  	WARN_ON_ONCE(s->ctor && (flags & __GFP_ZERO));
>  
> +	if (node == NUMA_NO_NODE)
> +		node = numa_mem_id();
> +	else if (!node_present_pages(node))
> +		node = node_to_mem_node(node);
> +
>  	freelist = get_partial(s, flags, node, c);
>  
>  	if (freelist)
> @@ -2569,12 +2568,10 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>  redo:
>  
>  	if (unlikely(!node_match(page, node))) {
> -		int searchnode = node;
> -
>  		if (node != NUMA_NO_NODE && !node_present_pages(node))
> -			searchnode = node_to_mem_node(node);
> +			node = node_to_mem_node(node);
>  
> -		if (unlikely(!node_match(page, searchnode))) {
> +		if (unlikely(!node_match(page, node))) {
>  			stat(s, ALLOC_NODE_MISMATCH);
>  			deactivate_slab(s, page, c->freelist, c);
>  			goto new_slab;
>