linux-kernel - Re: [RFC 12/15] xarray: Implement migration function for objects

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Message-ID: <20190312001602.GB25059@tower.DHCP.thefacebook.com>
Date:   Tue, 12 Mar 2019 00:16:07 +0000
From:   Roman Gushchin <guro@...com>
To:     "Tobin C. Harding" <tobin@...nel.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...helsinki.fi>,
        Matthew Wilcox <willy@...radead.org>,
        Tycho Andersen <tycho@...ho.ws>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 12/15] xarray: Implement migration function for objects

On Fri, Mar 08, 2019 at 03:14:23PM +1100, Tobin C. Harding wrote:
> Implement functions to migrate objects. This is based on
> initial code by Matthew Wilcox and was modified to work with
> slab object migration.
> 
> Co-developed-by: Christoph Lameter <cl@...ux.com>
> Signed-off-by: Tobin C. Harding <tobin@...nel.org>
> ---
>  lib/radix-tree.c | 13 +++++++++++++
>  lib/xarray.c     | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 14d51548bea6..9412c2853726 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -1613,6 +1613,17 @@ static int radix_tree_cpu_dead(unsigned int cpu)
>  	return 0;
>  }
>  
> +extern void xa_object_migrate(void *tree_node, int numa_node);
> +
> +static void radix_tree_migrate(struct kmem_cache *s, void **objects, int nr,
> +			       int node, void *private)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr; i++)
> +		xa_object_migrate(objects[i], node);
> +}
> +
>  void __init radix_tree_init(void)
>  {
>  	int ret;
> @@ -1627,4 +1638,6 @@ void __init radix_tree_init(void)
>  	ret = cpuhp_setup_state_nocalls(CPUHP_RADIX_DEAD, "lib/radix:dead",
>  					NULL, radix_tree_cpu_dead);
>  	WARN_ON(ret < 0);
> +	kmem_cache_setup_mobility(radix_tree_node_cachep, NULL,
> +				  radix_tree_migrate);
>  }
> diff --git a/lib/xarray.c b/lib/xarray.c
> index 81c3171ddde9..4f6f17c87769 100644
> --- a/lib/xarray.c
> +++ b/lib/xarray.c
> @@ -1950,6 +1950,50 @@ void xa_destroy(struct xarray *xa)
>  }
>  EXPORT_SYMBOL(xa_destroy);
>  
> +void xa_object_migrate(struct xa_node *node, int numa_node)
> +{
> +	struct xarray *xa = READ_ONCE(node->array);
> +	void __rcu **slot;
> +	struct xa_node *new_node;
> +	int i;
> +
> +	/* Freed or not yet in tree then skip */
> +	if (!xa || xa == XA_FREE_MARK)
> +		return;

XA_FREE_MARK is equal to 0, so the second check is redundant.

#define XA_MARK_0		((__force xa_mark_t)0U)
#define XA_MARK_1		((__force xa_mark_t)1U)
#define XA_MARK_2		((__force xa_mark_t)2U)
#define XA_PRESENT		((__force xa_mark_t)8U)
#define XA_MARK_MAX		XA_MARK_2
#define XA_FREE_MARK		XA_MARK_0

xa_node_free() sets node->array to XA_RCU_FREE, so maybe it's
what you need. I'm not sure however, Matthew should know better.

> +
> +	new_node = kmem_cache_alloc_node(radix_tree_node_cachep,
> +					 GFP_KERNEL, numa_node);

We need to check here if the allocation was successful.

Thanks!