One weakness which was introduced when the buffer LRU went away was
that GFP_NOFS allocations became equivalent to GFP_NOIO.  Because all
writeback goes via writepage/writepages, which requires entry into the
filesystem.

However now that swapout no longer calls bmap(), we can honour
GFP_NOFS's intent for swapcache pages.  So if the allocation request
specifies __GFP_IO and !__GFP_FS, we can wait on swapcache pages and we
can perform swapcache writeout.

This should strengthen the VM somewhat.

The set_page_buffers() and clear_page_buffers() macros are each used in
only one place.  Fold them into their callers.

highmem.h includes bio.h, so just about every compilation unit in the
kernel gets to process bio.h.

The patch moves the BIO-related functions out of highmem.h and into
bio-related headers.  The nested include is removed and all files which
need to include bio.h now do so.

alloc_bufer_head() does not need the additional argument - GFP_NOFS is
always correct.

Clean up ext3's journal_try_to_free_buffers().  Now that the
releasepage() a_op is non-blocking and need not perform I/O, this
function becomes much simpler.

bio_copy is doing

	vfrom = kmap_atomic(bv->bv_page, KM_BIO_IRQ);
	vto = kmap_atomic(bbv->bv_page, KM_BIO_IRQ);

which, if I understand atomic kmaps, is incorrect.  Both source and
dest will get the same pte.

The patch creates a separate atomic kmap member for the destination and
source of this copy.

Fix the loop driver for loop-on-blockdev setups.

When presented with a multipage BIO, loop_make_request overindexes the
first page and corrupts kernel memory.  Fix it to walk the individual
pages.

BTW, I suspect the IV handling in loop may be incorrect for multipage
BIOs.  Should we not be recalculating the IV for each page in the BIOs,
or incrementing the offset by the size of the preceding pages, or such?

This patch changes the swap I/O handling.  The objectives are:

- Remove swap special-casing
- Stop using buffer_heads -> direct-to-BIO
- Make S_ISREG swapfiles more robust.

I've spent quite some time with swap.  The first patches converted swap to
use block_read/write_full_page().  These were discarded because they are
still using buffer_heads, and a reasonable amount of otherwise unnecessary
infrastructure had to be added to the swap code just to make it look like a
regular fs.  So this code just has a custom direct-to-BIO path for swap,
which seems to be the most comfortable approach.

A significant thing here is the introduction of "swap extents".  A swap
extent is a simple data structure which maps a range of swap pages onto a
range of disk sectors.  It is simply:

	struct swap_extent {
		struct list_head list;
		pgoff_t start_page;
		pgoff_t nr_pages;
		sector_t start_block;
	};

At swapon time (for an S_ISREG swapfile), each block in the file is bmapped()
and the block numbers are parsed to generate the device's swap extent list.
This extent list is quite compact - a 512 megabyte swapfile generates about
130 nodes in the list.  That's about 4 kbytes of storage.  The conversion
from filesystem blocksize blocks into PAGE_SIZE blocks is performed at swapon
time.

At swapon time (for an S_ISBLK swapfile), we install a single swap extent
which describes the entire device.

The advantages of the swap extents are:

1: We never have to run bmap() (ie: read from disk) at swapout time.  So
   S_ISREG swapfiles are now just as robust as S_ISBLK swapfiles.

2: All the differences between S_ISBLK swapfiles and S_ISREG swapfiles are
   handled at swapon time.  During normal operation, we just don't care.
   Both types of swapfiles are handled the same way.

3: The extent lists always operate in PAGE_SIZE units.  So the problems of
   going from fs blocksize to PAGE_SIZE are handled at swapon time and normal
   operating code doesn't need to care.

4: Because we don't have to fiddle with different blocksizes, we can go
   direct-to-BIO for swap_readpage() and swap_writepage().  This introduces
   the kernel-wide invariant "anonymous pages never have buffers attached",
   which cleans some things up nicely.  All those block_flushpage() calls in
   the swap code simply go away.

5: The kernel no longer has to allocate both buffer_heads and BIOs to
   perform swapout.  Just a BIO.

6: It permits us to perform swapcache writeout and throttling for
   GFP_NOFS allocations (a later patch).

(Well, there is one sort of anon page which can have buffers: the pages which
are cast adrift in truncate_complete_page() because do_invalidatepage()
failed.  But these pages are never added to swapcache, and nobody except the
VM LRU has to deal with them).

The swapfile parser in setup_swap_extents() will attempt to extract the
largest possible number of PAGE_SIZE-sized and PAGE_SIZE-aligned chunks of
disk from the S_ISREG swapfile.  Any stray blocks (due to file
discontiguities) are simply discarded - we never swap to those.

If an S_ISREG swapfile is found to have any unmapped blocks (file holes) then
the swapon attempt will fail.

The extent list can be quite large (hundreds of nodes for a gigabyte S_ISREG
swapfile).  It needs to be consulted once for each page within
swap_readpage() and swap_writepage().  Hence there is a risk that we could
blow significant amounts of CPU walking that list.  However I have
implemented a "where we found the last block" cache, which is used as the
starting point for the next search.  Empirical testing indicates that this is
wildly effective - the average length of the list walk in map_swap_page() is
0.3 iterations per page, with a 130-element list.

It _could_ be that some workloads do start suffering long walks in that code,
and perhaps a tree would be needed there.  But I doubt that, and if this is
happening then it means that we're seeking all over the disk for swap I/O,
and the list walk is the least of our problems.

rw_swap_page_nolock() now takes a page*, not a kernel virtual address.  It
has been renamed to rw_swap_page_sync() and it takes care of locking and
unlocking the page itself.  Which is all a much better interface.

Support for type 0 swap has been removed.  Current versions of mkwap(8) seem
to never produce v0 swap unless you explicitly ask for it, so I doubt if this
will affect anyone.  If you _do_ have a type 0 swapfile, swapon will fail and
the message

	version 0 swap is no longer supported. Use mkswap -v1 /dev/sdb3

is printed.  We can remove that code for real later on.  Really, all that
swapfile header parsing should be pushed out to userspace.

This code always uses single-page BIOs for swapin and swapout.  I have an
additional patch which converts swap to use mpage_writepages(), so we swap
out in 16-page BIOs.  It works fine, but I don't intend to submit that.
There just doesn't seem to be any significant advantage to it.

I can't see anything in sys_swapon()/sys_swapoff() which needs the
lock_kernel() calls, so I deleted them.

If you ftruncate an S_ISREG swapfile to a shorter size while it is in use,
subsequent swapout will destroy the filesystem.  It was always thus, but it
is much, much easier to do now.  Not really a kernel problem, but swapon(8)
should not be allowing the kernel to use swapfiles which are modifiable by
unprivileged users.

Convert swap pages so that they are PageWriteback and !PageLocked while
under writeout, like all other block-backed pages.  (Network
filesystems aren't doing this yet - their pages are still locked while
under writeout)

buffer_insert_list() is showing up on Anton's graphs.  It'll be via
ext2's mark_buffer_dirty_inode() against indirect blocks.  If the
buffer is already on an inode queue, we know that it is on the correct
inode's queue so we don't need to re-add it.

The request queue was increased from 256 slots to 512 in 2.5.20.  The
throughput of `dbench 128' on Randy's 384 megabyte machine fell 40%.

We do need to understand why that happened, and what we can learn from
it.  But in the meanwhile I'd suggest that we go back to 256 slots so
that this known problem doesn't impact people's evaluation and tuning
of 2.5 performance.

mark_buffer_dirty() is showing up on Anton's graphs.  Avoiding the
buslocked RMW if the buffer is already dirty should fix that up.

- If grab_cache_page_nowait() is to be called while holding a lock on
  a different page, it must perform memory allocations with GFP_NOFS.
  Otherwise it could come back onto the locked page (if it's dirty) and
  deadlock.

  Also tidy this function up a bit - the checks in there were overly
  paranoid.

- In a few of places, look to see if we can avoid a buslocked cycle
  and dirtying of a cacheline.

Remove unneeded do_update_atime(), and convert update_atime() to C.

Stephen and Neil Brown recently worked this out.  It's a
rare situation which only affects data=journal mode.

Fix problem in data=journal mode where writeback could be left pending on a
journaled, deleted disk block.  If that block then gets reallocated, we can
end up with an alias in which the old data can be written back to disk over
the new.  Thanks to Neil Brown for spotting this and coming up with the
initial fix.

Adds five sysctls for tuning the writeback behaviour:

	dirty_async_ratio
	dirty_background_ratio
	dirty_sync_ratio
	dirty_expire_centisecs
	dirty_writeback_centisecs

these are described in Documentation/filesystems/proc.txt  They are
basically the tradiditional knobs which we've always had...

We are accreting a ton of obsolete sysctl numbers under /proc/sys/vm/.
I didn't recycle these - just mark them unused and remove the obsolete
documentation.

Ironically enough, both were written by me.

Fixed thus.

Add change_page_attr to change page attributes for the kernel linear map.

Fix AGP driver to use change_page_attr for the AGP buffer.

Clean up AGP driver a bit (only tested on i386/VIA+AMD)

Change ioremap_nocache to use change_page_attr to avoid mappings with
conflicting caching attributes.

This exports the pci_bus_type symbol to modules, needed by (at least)
the recent changes in pcmcia/cardbus.c.

This was done by inspection, is it OK Anton?  It's very simple:

into home.transmeta.com:/home/torvalds/v2.5/linux

This patch removes the concept of "logical" CPU numbers, in
preparation for CPU hotplugging.

Summary: 2.5.17 broke initrd on x86. Fix below.

Why: Kai's patch in 2.5.17 to move x86-specific options from
Makefile to arch/i386/boot/Makefile unfortunately lost the fact
that the orginal "#export RAMDISK = -DRAMDISK=512" statement
was commented out. (I suspect a typo.) RAMDISK is obsolete since
1.3.something, and uncommenting it has "interesting" effects
since the ram_size field has a very different meaning now.

The patch below reverts the statement to its pre-2.5.17 state.
Perhaps it should be removed altogether?

into home.transmeta.com:/home/torvalds/v2.5/linux

This patch splits fput into fput and __fput.  __fput is needed by aio to
construct a mechanism for performing a deferred fput during io
completion, which typically occurs during interrupt context.

This adds support for wait queue function callbacks, which are used by
aio to build async read / write operations on top of existing wait
queues at points that would normally block a process.

This patch switches SCSI from a bottom half to a tasklet.  It's been
reviewed, tested & approved by Andrew Morton, James Bottomley & Doug
Gilbert.

I took a quick look at why 2.5.21 hung at boot detecting partitions,
because a 2.5.22 did the exact same thing on my test box today... The
tcq locking is completely screwed now, and as I said before the weekend
I think the entire locking is just getting worse now.

Anyways, this patch at least attempts to make tcq follow the channel
lock usage to make it work for me.

Attached patch brings over the sane bits from 2.4-ac: i.e. if Linus
merges this and Alan merges your patch minus my complaints, the two
trees will be in sync...