On 04/08/17 11:12, Michal Hocko wrote:

On Fri 04-08-17 11:02:46, Igor Stoppa wrote:

[...]

quoted

struct page {
  /* First double word block */
  unsigned long flags;		/* Atomic flags, some possibly
				 * updated asynchronously */
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.
					 */
...
}

mapping seems to be used exclusively in 2 ways, based on the value of
its lower bit.

Not really. The above applies to LRU pages. Please note that Slab pages
use s_mem and huge pages use compound_mapcount. If vmalloc pages are
using none of those already you can add a new field there.

Yes, both from reading the code and some experimentation, it seems that
vmalloc is not using either field.

I'll add a vm_area field as you advised.

Is this something I could send as standalone patch?

--
thank you, igor

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