[PATCH] updated version of radix-tree pagecache

[Christoph Hellwig <hch@caldera.de>]

I've just uploaded an updated version of Momchil Velikov's patch for a
scalable pagecache using radix trees.  The patch can be found at:

	ftp://ftp.kernel.org/pub/linux/kernel/people/hch/patches/v2.4/2.4.17/linux-2.4.17-ratpagecache.patch.gz

	ftp://ftp.kernel.org/pub/linux/kernel/people/hch/patches/v2.4/2.4.17/linux-2.4.17-ratpagecache.patch.bz2

It contains a number of fixed and improvements by Momchil and me.

The basic advantage over the old version (besides the fixes :)) is that
the radix tree implementation is now independand of struct page /
struct address_space and thus can easily be used in other code.



=== Changelog ===


Momchil Velikov:

  - It was possible to return a PG_locked page to the buddy
    allocator with a subsequent oops, if the call to rat_insert in
    __add_to_page_cache failed.  Thus the functions is changed as to
    avoid modifying the pages before rat_insert was
    successful. Somewhat paranoid, I changed add_page_cache_locked
    too.
  - shmem_writepage was causing an infinite looping deadlock, when a
    couple of processes was yielding for kswapd, _including kswapd
    itself_.
  - Initialized swapper_space. On some architectures the spinlock is
    initilized to 0 on some to 1, who knows maybe there are/will be
    others. I have no idea why this didn't break the test on OSDL's
    4- and 8-way boxes.

Me:

  - moved rat.c from mm/ to lib/.
  - new structure: rat_root containing root-node, height and gfp_mask.
  - changed rat_* arguments to struct rat_root * and void *.
  - change struct page * arguments to void *.
  - moved all declarations in rat.h that are not public to rat.c
  - replaced  page_cache_init() by ratcache_init() in rat.c.
  - rat_node slab handling moved to rat.c
  - in swap_state.c removed 0/NULL initializers that aren't needed.
  - replaced __find_get_page/__find_lock_page with non-prefixed versions.
  - added kdoc-style comments to rat.c.
  - fixed up whitespaces in function declarations to math Linux style.