Re: [PATCH 1/1] ksm: introduce ksm_max_page_sharing per page deduplication limit

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 10 Nov 2015 19:44:41 +0100 Andrea Arcangeli <aarcange@redhat.com> wrote:

> The STABLE_NODE_DUP_HEAD must be an unique valid pointer never used
> elsewhere in any stable_node->head/node to avoid a clashes with the
> stable_node->node.rb_parent_color pointer, and different from
> &migrate_nodes. So the second field of &migrate_nodes is picked and
> verified as always safe with a BUILD_BUG_ON in case the list_head
> implementation changes in the future.
> 
> ...
>
> +	/*
> +	 * We need the second aligned pointer of the migrate_nodes
> +	 * list_head to stay clear from the rb_parent_color union
> +	 * (aligned and different than any node) and also different
> +	 * from &migrate_nodes. This will verify that future list.h changes
> +	 * don't break STABLE_NODE_DUP_HEAD.
> +	 */
> +	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
> +	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);

mm/ksm.c: In function 'remove_node_from_stable_tree':
mm/ksm.c:618: error: call to '__compiletime_assert_618' declared with attribute error: BUILD_BUG_ON failed: STABLE_NODE_DUP_HEAD <= &migrate_nodes
mm/ksm.c:619: error: call to '__compiletime_assert_619' declared with attribute error: BUILD_BUG_ON failed: STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1

That's with gcc-4.4.4.

I don't have time at present to investigate so I'll switch them to
WARN_ON_ONCE for now.


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>