On Mon, Aug 07, 2017 at 02:26:21PM +0300, Igor Stoppa wrote:

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

quoted

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

[...]

quoted

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?

Note that vmalloc() is not the only thing that use vmalloc address
space. There is also vmap() and i know one set of drivers that use
vmap() and also use the mapping field of struct page namely GPU
drivers.

So like i said previously i would store a flag inside vm_struct to
know if page you are looking at are pmalloc or not. Again do you
need to store something per page ? Would storing it per vm_struct
not be enough ?

Cheers,
J?r?me
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