On Wed, 16 Oct 2013, Joonsoo Kim wrote:
> - * see PAGE_MAPPING_ANON below.
> - */
> + union {
> + struct address_space *mapping; /* If low bit clear, points to
> + * inode address_space, or NULL.
> + * If page mapped as anonymous
> + * memory, low bit is set, and
> + * it points to anon_vma object:
> + * see PAGE_MAPPING_ANON below.
> + */
> + void *s_mem; /* slab first object */
> + };
The overloading of mapping has caused problems in the past since slab
pages are (or are they no longer?) used for DMA to disk. At that point the
I/O subsystem may be expecting a mapping in the page struct if this field
is not NULL.
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