Re: page flags ?

[Andrew Morton <akpm@osdl.org>]

Andy Whitcroft <apw@shadowen.org> wrote:
>
>  > How many bits are spare now?  ZONETABLE_PGSHIFT hurts my brain.
> 
>  The short answer is that on 32 bit architectures there are 24 bits
>  allocated to general page flags, page-flags.h indicates that 21 are
>  currently assigned so assuming it is accurate there are currently 3 bits
>  free.

Yipes, I didn't realise we were that close.

We can reclaim PG_highmem, use page_zone(page)->highmem

We can probably reclaim PG_slab

We can conceivably reclaim PG_swapcache, although that stuff got ugly.

Would dearly love to nuke PG_reserved, but everybody's scared of that ;)

PG_uncached is currently ia64-only and could conceivably be moved to bit
32, except there are rumours that arm might want to use it someday.

It's a bit irritating that swsusp uses two flags.

I don't see any other low-hanging fruit there.
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