linux-kernel - Re: [RFC PATCH v2 09/14] xarray: Implement migration function for objects

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Message-ID: <20190403172326.GJ22763@bombadil.infradead.org>
Date:   Wed, 3 Apr 2019 10:23:26 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     "Tobin C. Harding" <tobin@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Alexander Viro <viro@....linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Pekka Enberg <penberg@...helsinki.fi>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Christopher Lameter <cl@...ux.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Waiman Long <longman@...hat.com>,
        Tycho Andersen <tycho@...ho.ws>, Theodore Ts'o <tytso@....edu>,
        Andi Kleen <ak@...ux.intel.com>,
        David Chinner <david@...morbit.com>,
        Nick Piggin <npiggin@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 09/14] xarray: Implement migration function for
 objects

On Wed, Apr 03, 2019 at 03:21:22PM +1100, Tobin C. Harding wrote:
> +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_RCU_FREE)
> +		return;
> +
> +	new_node = kmem_cache_alloc_node(radix_tree_node_cachep,
> +					 GFP_KERNEL, numa_node);
> +	if (!new_node)
> +		return;
> +
> +	xa_lock_irq(xa);
> +
> +	/* Check again..... */
> +	if (xa != node->array || !list_empty(&node->private_list)) {
> +		node = new_node;
> +		goto unlock;
> +	}
> +
> +	memcpy(new_node, node, sizeof(struct xa_node));
> +
> +	/* Move pointers to new node */
> +	INIT_LIST_HEAD(&new_node->private_list);

Surely we can do something more clever, like ...

	if (xa != node->array) {
...
	if (list_empty(&node->private_list))
		INIT_LIST_HEAD(&new_node->private_list);
	else
		list_replace(&node->private_list, &new_node->private_list);


BTW, the raidx tree nodes / xa_nodes share the same slab cache; we need
to finish converting all radix tree & IDR users to the XArray before
this series can go in.