Somewhat happier in gcc 3.2 this way

into penguin.transmeta.com:/home/penguin/torvalds/repositories/kernel/linux

Fix compilation errors for do_fork() and print_symbol()

into penguin.transmeta.com:/home/penguin/torvalds/repositories/kernel/linux

Implements a new set of block address_space_operations which will never
attach buffer_heads to file pagecache.  These can be turned on for ext2
with the `nobh' mount option.

During write-intensive testing on a 7G machine, total buffer_head
storage remained below 0.3 megabytes.  And those buffer_heads are
against ZONE_NORMAL pagecache and will be reclaimed by ZONE_NORMAL
memory pressure.

This work is, of course, a special for the huge highmem machines.
Possibly it obsoletes the buffer_heads_over_limit stuff (which doesn't
work terribly well), but that code is simple, and will provide relief
for other filesystems.


It should be noted that the nobh_prepare_write() function and the
PageMappedToDisk() infrastructure is what is needed to solve the
problem of user data corruption when the filesystem which backs a
sparse MAP_SHARED mapping runs out of space.  We can use this code in
filemap_nopage() to ensure that all mapped pages have space allocated
on-disk.  Deliver SIGBUS on ENOSPC.

This will require a new address_space op, I expect.

This patch is a general solution to the situation where a zone is full
of pinned pages.

This can come about if:

a) Someone has allocated all of ZONE_DMA for IO buffers

b) Some application is mlocking some memory and a zone ends up full
   of mlocked pages (can happen on a 1G ia32 system)

c) All of ZONE_HIGHMEM is pinned in hugetlb pages (can happen on 1G
   machines)

We'll currently burn 10% of CPU in kswapd when this happens, although
it is quite hard to trigger.

The algorithm is:

- If page reclaim has scanned 2 * the total number of pages in the
  zone and there have been no pages freed in that zone then mark the
  zone as "all unreclaimable".

- When a zone is "all unreclaimable" page reclaim almost ignores it.
  We will perform a "light" scan at DEF_PRIORITY (typically 1/4096'th of
  the zone, or 64 pages) and then forget about the zone.

- When a batch of pages are freed into the zone, clear its "all
  unreclaimable" state and start full scanning again.  The assumption
  being that some state change has come about which will make reclaim
  successful again.

  So if a "light scan" actually frees some pages, the zone will revert to
  normal state immediately.

So we're effectively putting the zone into "low power" mode, and lightly
polling it to see if something has changed.

The code works OK, but is quite hard to test - I mainly tested it by
pinning all highmem in hugetlb pages.

Strengthen the `incremental min' logic in the page allocator.

Currently it is allowing the allocation to succeed if the zone has
free_pages >= pages_high.

This was to avoid a lockup corner case in which all the zones were at
pages_high so reclaim wasn't doing anything, but the incremental min
refused to take pages from those zones anyway.

But we want the incremental min zone protection to work.  So:

- Only allow the allocator to dip below the incremental min if he
  cannot run direct reclaim.

- Change the page reclaim code so that on the direct reclaim path,
  the caller can free pages beyond ->pages_high.  So if the incremental
  min test fails, the caller will go and free some more memory.

  Eventually, the caller will have freed enough memory for the
  incremental min test to pass against one of the zones.

The vm_writeback address_space operation was designed to provide the VM
with a "clustered writeout" capability.  It allowed the filesystem to
perform more intelligent writearound decisions when the VM was trying
to clean a particular page.

I can't say I ever saw any real benefit from this - not much writeout
actually happens on that path - quite a lot of work has gone into
minimising it actually.

The default ->vm_writeback a_op which I provided wrote back the pages
in ->dirty_pages order.  But there is one scenario in which this causes
problems - writing a single 4G file with mem=4G.  We end up with all of
ZONE_NORMAL full of dirty pages, but all writeback effort is against
highmem pages.  (Because there is about 1.5G of dirty memory total).

Net effect: the machine stalls ZONE_NORMAL allocation attempts until
the ->dirty_pages writeback advances onto ZONE_NORMAL pages.

This can be fixed most sweetly with additional radix-tree
infrastructure which will be quite complex.  Later.


So this patch dumps it all, and goes back to using writepage
against individual pages as they come off the LRU.

blk_congestion_wait() is a utility function which various callers use
to throttle themselves to the rate at which the IO system can retire
writes.

The current implementation refuses to wait if no queues are "congested"
(>75% of requests are in flight).

That doesn't work if the queue is so huge that it can hold more than
40% (dirty_ratio) of memory.  The queue simply cannot enter congestion
because the VM refuses to allow more than 40% of memory to be dirtied.
(This spin could happen with a lot of normal-sized queues too)

So this patch simply changes blk_congestion_wait() to throttle even if
there are no congested queues.  It will cause the caller to sleep until
someone puts back a write request against any queue.  (Nobody uses
blk_congestion_wait for read congestion).

The patch adds new state to backing_dev_info->state: a couple of flags
which indicate whether there are _any_ reads or writes in flight
against that queue.  This was added to prevent blk_congestion_wait()
from taking a nap when there are no writes at all in flight.

But the "are there any reads" info could be used to defer background
writeout from pdflush, to reduce read-vs-write competition.  We'll see.

Because the large request queues have made a fundamental change:
blocking in get_request_wait() has been the main form of VM throttling
for years.  But with large queues it doesn't work any more - all
throttling happens in blk_congestion_wait().

Also, change io_schedule_timeout() to propagate the schedule_timeout()
return value.  I was using that in some debug code, but it should have
been like that from day one.

From Roman Zippel.  Don't assume that physical memory starts at
physical address zero.

Patch from Stephen Tweedie

"In looking at the fix for the ext3 Orlov double-accounting bug, I
 noticed a change to the sb->s_dir_count accounting, restoring a
 missing s_dir_count++ when we allocate a new directory.

 However, I can't find anywhere in the code where we decrement this
 again on directory deletion, neither in ext2 nor in ext3, in 2.4 nor
 in 2.5."

Locking is via lock_super().

There is a warning in there to detect when block_write_full_page()
attaches buffers to a blockdev page.  This is a bad thing because that
page's blocks may then overlap blocks from a different address_space.
So I disallowed it.

But the message can be triggered when an application is mmapping a
blockdev MAP_SHARED.  Apparently INND likes to do this.

So remove the warning.