From: Andrea Arcangeli <andrea@suse.de>

We need a barrier before checking for kthread_should_stop in do_stop.

From: Davide Libenzi <davidel@xmailserver.org>

When I split evenpoll_release() in an inline fast path plus an
eventpoll_release_file() slow path, I forgot to change comments.

From: Romain Francoise <romain@orebokech.com>

arch/sparc64/mm/hugetlbpage.c does not include linux/module.h so
EXPORT_SYMBOL prints out warnings, and since sparc64 Makefiles have
-Werror, the build fails.

From: Olof Johansson <olof@austin.ibm.com>

As discussed on the ppc64 list yesterday and today:

On some ppc64 systems, Open Firmware will give memory device nodes that are
only 16MB in size, instead of the 256MB that our NUMA code currently
expects (see MEMORY_INCREMENT in mmzone.h).

Just changing the defines from 256MB to 16MB makes the table blow up from
32KB to 512KB, so this patch also makes it dynamically allocated based on
actual memory size.  Since all this is done before (well, during) bootmem
init so we need to use lmb_alloc().

Finally, there's no need to use a full int for node ID. Current max is 16
nodes, so a signed char still leaves plenty of room to grow.

From: Ingo Molnar <mingo@elte.hu>

Dave reported that /proc/*/status sometimes shows 101% as LoadAVG, which
makes no sense.

the reason of the bug is slightly incorrect scaling of the load_avg value. 
The patch below fixes this.

From: Arjan van de Ven <arjanv@redhat.com>

Below is a patch to enable 4Kb stacks for x86. The goal of this is to

1) Reduce footprint per thread so that systems can run many more threads
   (for the java people)

2) Reduce the pressure on the VM for order > 0 allocations. We see real life
   workloads (granted with 2.4 but the fundamental fragmentation issue isn't
   solved in 2.6 and isn't solvable in theory) where this can be a problem.
   In addition order > 0 allocations can make the VM "stutter" and give more
   latency due to having to do much much more work trying to defragment

The first 2 bits of the patch actually affect compiler options in a generic
way: I propose to disable the -funit-at-a-time feature from gcc.  With this
enabled (and it's default with -O2), gcc will very agressively inline
functions, which is nice and all for userspace, but for the kernel this makes
us suffer a gcc deficiency more: gcc is extremely bad at sharing stackslots,
for example a situation like this:

if (some_condition)
	function_A();
else
	function_B();

with -funit-at-a-time, both function_A() and _B() might get inlined, however
the stack usage of both functions of the parent function grows the stack
usage of both functions COMBINED instead of the maximum of the two.  Even
with the normal 8Kb stacks this is a danger since we see some functions grow
3Kb to 4Kb of stack use this way.  With 4Kb stacks, 4Kb of stack usage growth
obviously is deadly ;-( but even with 8Kb stacks it's pure lottery.
Disabling -funit-at-a-time also exposes another thing in the -mm tree; the
attribute always_inline is considered harmful by gcc folks in that when gcc
makes a decision to NOT inline a function marked this way, it throws an
error.  Disabling -funit-at-a-time disables some of the agressive inlining
(eg of large functions that come later in the .c file) so this would make
your tree not compile.

The 4k stackness of the kernel is included in modversions, so people don't
load 4k-stack modules into 8k-stack kernels.

At present 4k stacks are selectable in config.  When the feature has settled
in we should remove the 8k option.  This will break the nvidia modules.  But
Fedora uses 4k stacks so a new nvidia driver is expected soon.

drivers/acpi/events/evmisc.c: In function `acpi_ev_queue_notify_request':
drivers/acpi/events/evmisc.c:143: warning: too many arguments for format

The filempa_nopage() logic will go into a tight loop if
do_page_cache_readahead() doesn't actually start I/O against the target page.
This can happen if the disk is read-congested, or if the filesystem doesn't
want to read that part of the file for some reason.

We will accidentally break out of the loop because

	 (ra->mmap_miss > ra->mmap_hit + MMAP_LOTSAMISS)

will eventually become true.

Fix that up.

Remove the hardwired pagefault readaround distance in filemap_nopage() and
use the per-file readahead setting.

The main reason for this is in fact laptop-mode.  If you want to prevent the
disk from spinning up then you want all of your application's pages to be
pulled into memory in one hit.  Otherwise the disk will spin up each time you
use a new part of whatever application(s) you are running.

From: Bart Samwel <bart@samwel.tk>

Add support for the value "0" to ext3's "commit" option.  When this value
is given, ext3 substitutes it by the default commit interval.  Introduce a
constant JBD_DEFAULT_MAX_COMMIT_AGE for this.

From: Bart Samwel <bart@samwel.tk>

Adds /proc/sys/vm/laptop-mode: a special knob which says "this is a laptop".
In this mode the kernel will attempt to avoid spinning disks up.

Algorithm: the idea is to hold dirty data in memory for a long time, but to
flush everything which has been accumulated if the disk happens to spin up
for other reasons.

- Whenever a disk request completes (read or write), schedule a timer a few
  seconds hence.  If the timer was already pending, reset it to a few seconds
  hence.

- When the timer expires, write back the whole world.  We use
  sync_filesystems() for this because it will force ext3 journal commits as
  well.

- In balance_dirty_pages(), kick off background writeback when we hit the
  high threshold (dirty_ratio), not when we hit the low threshold.  This has
  the effect of causing "lumpy" writeback which is something I spent a year
  fixing, but in laptop mode, it is desirable.

- In try_to_free_pages(), only kick pdflush if the VM is getting into
  distress: we want to keep scanning for clean pages, deferring writeback.

- In page reclaim, avoid writing back the odd random dirty page off the
  LRU: only start I/O if the scanning is working harder.

The effect is to perform a sync() a few seconds after all I/O has ceased.

The value which was written into /proc/sys/vm/laptop-mode determines, in
seconds, the delay between the final I/O and the flush.

Additionally, the patch adds tools which help answer the question "why the
heck does my disk spin up all the time?".  The user may set
/proc/sys/vm/block_dump to a non-zero value and the kernel will print out
information which will identify the process which is performing disk reads or
which is dirtying pagecache.

The user should probably disable syslogd before setting block-dump.

This is always equal to constant zero.

From: Hugh Dickins <hugh@veritas.com>

rmap's try_to_unmap_one comments on find_vma failure, that a page may
temporarily be absent from a vma during mremap: no longer, though it is still
possible for this find_vma to fail, while unmap_vmas drops page_table_lock
(but that is no problem for file truncation).

From: Hugh Dickins <hugh@veritas.com>

mremap's move_vma should think ahead to lessen the chance of failure during
its rewind on failure: running out of memory always possible, but it's silly
for it to embark when it's near the map_count limit.

From: Hugh Dickins <hugh@veritas.com>

Subtle point from Rajesh Venkatasubramanian: when mremap's move_vma fails and
so rewinds, before moving the file-based ptes back, we must move new_vma
before old vma in the i_mmap or i_mmap_shared list, so that when racing
against vmtruncate we cannot propagate pages to be truncated back from
new_vma into the just cleaned old_vma.

From: Hugh Dickins <hugh@veritas.com>

Partial rewrite of mremap's move_vma.  Rajesh Venkatasubramanian has pointed
out that vmtruncate could miss ptes, leaving orphaned pages, because move_vma
only made the new vma visible after filling it.  We see no good reason for
that, and time to make move_vma more robust.

Removed all its vma merging decisions, leave them to mmap.c's vma_merge, with
copy_vma added.  Removed duplicated is_mergeable_vma test from vma_merge, and
duplicated validate_mm from insert_vm_struct.

move_vma move from old to new then unmap old; but on error move back from new
to old and unmap new.  Don't unwind within move_page_tables, let move_vma
call it explicitly to unwind, with the right source vma.  Get the
VM_ACCOUNTing right even when the final do_munmap fails.

From: Hugh Dickins <hugh@veritas.com>

Clean up mremap move's copy_one_pte:

- get_one_pte_map_nested already weeded out the pte_none case,
  now don't even call copy_one_pte if it has nothing to do.

- check pfn_valid before passing page to page_remove_rmap.

From: Hugh Dickins <hugh@veritas.com>

First of six patches against 2.6.5-rc3, cleaning up mremap's move_vma, and
fixing truncation orphan issues raised by Rajesh Venkatasubramanian. 
Originally done as part of the anonymous objrmap work on mremap move, but
useful fixes now extracted for mainline.  The mremap changes need some
exposure in the -mm tree first, but the first (fork one-liner) is safe enough
to go straight into 2.6.5.



From: Rajesh Venkatasubramanian.  Despite the comment that child vma should
be inserted just after parent vma, 2.5.6 did exactly the reverse: thus a
racing vmtruncate may free the child's ptes, then advance to the parent, and
meanwhile copy_page_range has propagated more ptes from the parent to the
child, leaving file pages still mapped after truncation.

The compound page logic is a little fragile - it relies on additional
metadata in the pageframes which some other kernel code likes to stomp on
(xfs was doing this).

Also, because we're treating all higher-order pages as compound pages it is
no longer possible to free individual lower-order pages from the middle of
higher-order pages.  At least one ARM driver insists on doing this.

We only really need the compound page logic for higher-order pages which can
be mapped into user pagetables and placed under direct-io.  This covers
hugetlb pages and, conceivably, soundcard DMA buffers which were allcoated
with a higher-order allocation but which weren't marked PageReserved.

The patch arranges for the hugetlb implications to allocate their pages with
compound page metadata, and all other higher-order allocations go back to the
old way.

(Andrea supplied the GFP_LEVEL_MASK fix)

Rework the code layout a bit.  No logic change.

From: Jens Axboe <axboe@suse.de>

Takashi did some nice latency testing of the current kernel (with -mm
writeback changes), and the biggest offender in general core is
mpage_writepages().

The radix-tree walk for writeback has a couple of problems:

a) It always scans a file from its first dirty page, so if someone
   is repeatedly dirtying the front part of a file, pages near the end
   may be starved of writeout.  (Well, not completely: the `kupdate'
   function will write an entire file once the file's dirty timestamp
   has expired).  

b) When the disk queues are huge (10000 requests), there can be a
   very large number of locked pages.  Scanning past these in writeback
   consumes quite some CPU time.

So in each address_space we record the index at which the last batch of
writeout terminated and start the next batch of writeback from that
point.

If pdflush hits a locked-and-clean buffer in __block_write_full_page() it
will just pass over the buffer.  Typically the buffer is an ext3 data=ordered
buffer which is being written by kjournald, but a similar thing can happen
with blockdev buffers and ll_rw_block().

This is bad because the buffer is still under I/O and a subsequent fsync's
fdatawait() needs to know about it.

It is not practical to tag the page for writeback - only the submitter of the
I/O can do that, because the submitter has control of the end_io handler.

So instead, redirty the page so a subsequent fsync's fdatawrite() will wait on
the underway I/O.

There is a risk that pdflush::background_writeout() will lock up, repeatedly
trying and failing to write the same page.  This is prevented by ensuring
that background_writeout() always throttles when it made no progress.

fdatasync can fail to wait on some pages due to a race.

If some task (eg pdflush) is flushing the same mapping it can remove a page's
dirty tag but not then mark that page as being under writeback, because
pdflush hit a locked buffer in __block_write_full_page().  This will happen
because kjournald is writing the buffer.  In this situation
__block_write_full_page() will redirty the page so that fsync notices it, but
there is a window where the page eludes the radix tree dirty page walk.

Consequently a concurrent fsync will fail to notice the page when walking the
radix tree's dirty pages.

The approach taken by this patch is to leave the page marked as dirty in the
radix tree while ->writepage is working out what to do with it.  This ensures
that a concurrent write-for-sync will successfully locate the page and will
then block in lock_page() until the non-write-for-sync code has finished
altering the page state.

Remove the now-unneeded page.list field.

Switch the m68k pointer-table code over to page->lru.

Switch the ARM `small_page' code over to page->lru.

The compound page logic is using page->lru, and these get will scribbled on
in various places so switch the Compound page logic over to using ->mapping
and ->private.

The address_space.readapges() function currently takes a list of pages,
strung together via page->list.  Switch it to using page->lru.

This changes the API into filesystems.

Switch it to ->lru

Switch them over to page.lru

Switch the page allocator over to using page.lru for the buddy lists.

slab.c is using page->list.  Switch it over to using page->lru so we can
remove page.list.

This code is playing with page->lru from pages which came from slab.  But to
remove page->list we need to convert slab over to using page->lru.  So we
cannot allow the i386 pagetable code to go scribbling on the ->lru field of
active slab pages.

This optimisation was pretty thin, and it is more important to shrink the
pageframe (on all architectures).

Remove remaining references to address_space.clean_pages.

Instead, use a radix-tree walk of the pages which are tagged as being under
writeback.

The new function wait_on_page_writeback_range() was generalised out of
filemap_fdatawait().  We can later use this to provide concurrent fsync of
just a section of a file.

Now remove address_space.io_pages.

Juggle dirty pages and dirty inodes and dirty superblocks and various
different writeback modes and livelock avoidance and fairness to recover from
the loss of mapping->io_pages.

Move everything over to walking the radix tree via the PAGECACHE_TAG_DIRTY
tag.  Remove address_space.dirty_pages.

Arrange for under-writeback pages to be marked thus in their pagecache radix
tree.