mm: fix NULL ptr dereference in __count_immobile_pages

commit 687875fb7de4a95223af20ee024282fa9099f860 upstream.

Fix the following NULL ptr dereference caused by

  cat /sys/devices/system/memory/memory0/removable

Pid: 13979, comm: sed Not tainted 3.0.13-0.5-default #1 IBM BladeCenter LS21 -[7971PAM]-/Server Blade
RIP: __count_immobile_pages+0x4/0x100
Process sed (pid: 13979, threadinfo ffff880221c36000, task ffff88022e788480)
Call Trace:
  is_pageblock_removable_nolock+0x34/0x40
  is_mem_section_removable+0x74/0xf0
  show_mem_removable+0x41/0x70
  sysfs_read_file+0xfe/0x1c0
  vfs_read+0xc7/0x130
  sys_read+0x53/0xa0
  system_call_fastpath+0x16/0x1b

We are crashing because we are trying to dereference NULL zone which
came from pfn=0 (struct page ffffea0000000000). According to the boot
log this page is marked reserved:
e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)

and early_node_map confirms that:
early_node_map[3] active PFN ranges
    1: 0x00000010 -> 0x0000009c
    1: 0x00000100 -> 0x000bffa3
    1: 0x00100000 -> 0x00240000

The problem is that memory_present works in PAGE_SECTION_MASK aligned
blocks so the reserved range sneaks into the the section as well.  This
also means that free_area_init_node will not take care of those reserved
pages and they stay uninitialized.

When we try to read the removable status we walk through all available
sections and hope that the zone is valid for all pages in the section.
But this is not true in this case as the zone and nid are not initialized.

We have only one node in this particular case and it is marked as node=1
(rather than 0) and that made the problem visible because page_to_nid will
return 0 and there are no zones on the node.

Let's check that the zone is valid and that the given pfn falls into its
boundaries and mark the section not removable.  This might cause some
false positives, probably, but we do not have any sane way to find out
whether the page is reserved by the platform or it is just not used for
whatever other reasons.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
ext4: enforce bigalloc restrictions (e.g., no online resizing, etc.)

At least initially if the bigalloc feature is enabled, we will not
support non-extent mapped inodes, online resizing, online defrag, or
the FITRIM ioctl.  This simplifies the initial implementation.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
ext4: add missing ext4_resize_end on error paths

commit 014a1770371a028d22f364718c805f4216911ecd upstream.

Online resize ioctls 'EXT4_IOC_GROUP_EXTEND' and 'EXT4_IOC_GROUP_ADD'
call ext4_resize_begin() to check permissions and to set the
EXT4_RESIZING bit lock, they do their work and they must finish with
ext4_resize_end() which calls clear_bit_unlock() to unlock and to
avoid -EBUSY errors for the next resize operations.

This patch adds the missing ext4_resize_end() calls on error paths.

Patch tested.

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
ext4: add __user decoration to calls of copy_{from,to}_user()

This quiets the sparse noise:

warning: incorrect type in argument 2 (different address spaces)
   expected void const [noderef] <asn:1>*from
   got struct fstrim_range *<noident>
warning: incorrect type in argument 1 (different address spaces)
   expected void [noderef] <asn:1>*to
   got struct fstrim_range *<noident>

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
jbd: Issue cache flush after checkpointing

commit 353b67d8ced4dc53281c88150ad295e24bc4b4c5 upstream.

When we reach cleanup_journal_tail(), there is no guarantee that
checkpointed buffers are on a stable storage - especially if buffers were
written out by log_do_checkpoint(), they are likely to be only in disk's
caches. Thus when we update journal superblock, effectively removing old
transaction from journal, this write of superblock can get to stable storage
before those checkpointed buffers which can result in filesystem corruption
after a crash.

A similar problem can happen if we replay the journal and wipe it before
flushing disk's caches.

Thus we must unconditionally issue a cache flush before we update journal
superblock in these cases. The fix is slightly complicated by the fact that we
have to get log tail before we issue cache flush but we can store it in the
journal superblock only after the cache flush. Otherwise we risk races where
new tail is written before appropriate cache flush is finished.

I managed to reproduce the corruption using somewhat tweaked Chris Mason's
barrier-test scheduler. Also this should fix occasional reports of 'Bit already
freed' filesystem errors which are totally unreproducible but inspection of
several fs images I've gathered over time points to a problem like this.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Scm: Remove unnecessary pid & credential references in Unix socket's send and receive path

Patch series 109f6e39..7361c36c back in 2.6.36 added functionality to
allow credentials to work across pid namespaces for packets sent via
UNIX sockets.  However, the atomic reference counts on pid and
credentials caused plenty of cache bouncing when there are numerous
threads of the same pid sharing a UNIX socket.  This patch mitigates the
problem by eliminating extraneous reference counts on pid and
credentials on both send and receive path of UNIX sockets. I found a 2x
improvement in hackbench's threaded case.

On the receive path in unix_dgram_recvmsg, currently there is an
increment of reference count on pid and credentials in scm_set_cred.
Then there are two decrement of the reference counts.  Once in scm_recv
and once when skb_free_datagram call skb->destructor function
unix_destruct_scm.  One pair of increment and decrement of ref count on
pid and credentials can be eliminated from the receive path.  Until we
destroy the skb, we already set a reference when we created the skb on
the send side.

On the send path, there are two increments of ref count on pid and
credentials, once in scm_send and once in unix_scm_to_skb.  Then there
is a decrement of the reference counts in scm_destroy's call to
scm_destroy_cred at the end of unix_dgram_sendmsg functions.   One pair
of increment and decrement of the reference counts can be removed so we
only need to increment the ref counts once.

By incorporating these changes, for hackbench running on a 4 socket
NHM-EX machine with 40 cores, the execution of hackbench on
50 groups of 20 threads sped up by factor of 2.

Hackbench command used for testing:
./hackbench 50 thread 2000

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Revert "Scm: Remove unnecessary pid & credential references in Unix socket's send and receive path"

This reverts commit 0856a304091b33a8e8f9f9c98e776f425af2b625.

As requested by Eric Dumazet, it has various ref-counting
problems and has introduced regressions.  Eric will add
a more suitable version of this performance fix.

Signed-off-by: David S. Miller <davem@davemloft.net>
af_unix: dont send SCM_CREDENTIALS by default

Since commit 7361c36c5224 (af_unix: Allow credentials to work across
user and pid namespaces) af_unix performance dropped a lot.

This is because we now take a reference on pid and cred in each write(),
and release them in read(), usually done from another process,
eventually from another cpu. This triggers false sharing.

# Events: 154K cycles
#
# Overhead  Command       Shared Object        Symbol
# ........  .......  ..................  .........................
#
    10.40%  hackbench  [kernel.kallsyms]   [k] put_pid
     8.60%  hackbench  [kernel.kallsyms]   [k] unix_stream_recvmsg
     7.87%  hackbench  [kernel.kallsyms]   [k] unix_stream_sendmsg
     6.11%  hackbench  [kernel.kallsyms]   [k] do_raw_spin_lock
     4.95%  hackbench  [kernel.kallsyms]   [k] unix_scm_to_skb
     4.87%  hackbench  [kernel.kallsyms]   [k] pid_nr_ns
     4.34%  hackbench  [kernel.kallsyms]   [k] cred_to_ucred
     2.39%  hackbench  [kernel.kallsyms]   [k] unix_destruct_scm
     2.24%  hackbench  [kernel.kallsyms]   [k] sub_preempt_count
     1.75%  hackbench  [kernel.kallsyms]   [k] fget_light
     1.51%  hackbench  [kernel.kallsyms]   [k]
__mutex_lock_interruptible_slowpath
     1.42%  hackbench  [kernel.kallsyms]   [k] sock_alloc_send_pskb

This patch includes SCM_CREDENTIALS information in a af_unix message/skb
only if requested by the sender, [man 7 unix for details how to include
ancillary data using sendmsg() system call]

Note: This might break buggy applications that expected SCM_CREDENTIAL
from an unaware write() system call, and receiver not using SO_PASSCRED
socket option.

If SOCK_PASSCRED is set on source or destination socket, we still
include credentials for mere write() syscalls.

Performance boost in hackbench : more than 50% gain on a 16 thread
machine (2 quad-core cpus, 2 threads per core)

hackbench 20 thread 2000

4.228 sec instead of 9.102 sec

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
AF_UNIX: Fix poll blocking problem when reading from a stream socket

poll() call may be blocked by concurrent reading from the same stream
socket.

Signed-off-by: Alexey Moiseytsev <himeraster@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
af_unix: fix EPOLLET regression for stream sockets

[ Upstream commit 6f01fd6e6f6809061b56e78f1e8d143099716d70 ]

Commit 0884d7aa24 (AF_UNIX: Fix poll blocking problem when reading from
a stream socket) added a regression for epoll() in Edge Triggered mode
(EPOLLET)

Appropriate fix is to use skb_peek()/skb_unlink() instead of
skb_dequeue(), and only call skb_unlink() when skb is fully consumed.

This remove the need to requeue a partial skb into sk_receive_queue head
and the extra sk->sk_data_ready() calls that added the regression.

This is safe because once skb is given to sk_receive_queue, it is not
modified by a writer, and readers are serialized by u->readlock mutex.

This also reduce number of spinlock acquisition for small reads or
MSG_PEEK users so should improve overall performance.

Reported-by: Nick Mathewson <nickm@freehaven.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Alexey Moiseytsev <himeraster@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
mm: change isolate mode from #define to bitwise type

Change ISOLATE_XXX macro with bitwise isolate_mode_t type.  Normally,
macro isn't recommended as it's type-unsafe and making debugging harder as
symbol cannot be passed throught to the debugger.

Quote from Johannes
" Hmm, it would probably be cleaner to fully convert the isolation mode
into independent flags.  INACTIVE, ACTIVE, BOTH is currently a
tri-state among flags, which is a bit ugly."

This patch moves isolate mode from swap.h to mmzone.h by memcontrol.h

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: compaction: make isolate_lru_page() filter-aware

In async mode, compaction doesn't migrate dirty or writeback pages.  So,
it's meaningless to pick the page and re-add it to lru list.

Of course, when we isolate the page in compaction, the page might be dirty
or writeback but when we try to migrate the page, the page would be not
dirty, writeback.  So it could be migrated.  But it's very unlikely as
isolate and migration cycle is much faster than writeout.

So, this patch helps cpu overhead and prevent unnecessary LRU churning.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: zone_reclaim: make isolate_lru_page() filter-aware

In __zone_reclaim case, we don't want to shrink mapped page.  Nonetheless,
we have isolated mapped page and re-add it into LRU's head.  It's
unnecessary CPU overhead and makes LRU churning.

Of course, when we isolate the page, the page might be mapped but when we
try to migrate the page, the page would be not mapped.  So it could be
migrated.  But race is rare and although it happens, it's no big deal.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
vmscan: add block plug for page reclaim

per-task block plug can reduce block queue lock contention and increase
request merge.  Currently page reclaim doesn't support it.  I originally
thought page reclaim doesn't need it, because kswapd thread count is
limited and file cache write is done at flusher mostly.

When I test a workload with heavy swap in a 4-node machine, each CPU is
doing direct page reclaim and swap.  This causes block queue lock
contention.  In my test, without below patch, the CPU utilization is about
2% ~ 7%.  With the patch, the CPU utilization is about 1% ~ 3%.  Disk
throughput isn't changed.  This should improve normal kswapd write and
file cache write too (increase request merge for example), but might not
be so obvious as I explain above.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: drop nr_force_scan[] from get_scan_count

The nr_force_scan[] tuple holds the effective scan numbers for anon and
file pages in case the situation called for a forced scan and the
regularly calculated scan numbers turned out zero.

However, the effective scan number can always be assumed to be
SWAP_CLUSTER_MAX right before the division into anon and file.  The
numerators and denominator are properly set up for all cases, be it force
scan for just file, just anon, or both, to do the right thing.

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Ying Han <yinghan@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: do not writeback filesystem pages in direct reclaim

Testing from the XFS folk revealed that there is still too much I/O from
the end of the LRU in kswapd.  Previously it was considered acceptable by
VM people for a small number of pages to be written back from reclaim with
testing generally showing about 0.3% of pages reclaimed were written back
(higher if memory was low).  That writing back a small number of pages is
ok has been heavily disputed for quite some time and Dave Chinner
explained it well;

	It doesn't have to be a very high number to be a problem. IO
	is orders of magnitude slower than the CPU time it takes to
	flush a page, so the cost of making a bad flush decision is
	very high. And single page writeback from the LRU is almost
	always a bad flush decision.

To complicate matters, filesystems respond very differently to requests
from reclaim according to Christoph Hellwig;

	xfs tries to write it back if the requester is kswapd
	ext4 ignores the request if it's a delayed allocation
	btrfs ignores the request

As a result, each filesystem has different performance characteristics
when under memory pressure and there are many pages being dirtied.  In
some cases, the request is ignored entirely so the VM cannot depend on the
IO being dispatched.

The objective of this series is to reduce writing of filesystem-backed
pages from reclaim, play nicely with writeback that is already in progress
and throttle reclaim appropriately when writeback pages are encountered.
The assumption is that the flushers will always write pages faster than if
reclaim issues the IO.

A secondary goal is to avoid the problem whereby direct reclaim splices
two potentially deep call stacks together.

There is a potential new problem as reclaim has less control over how long
before a page in a particularly zone or container is cleaned and direct
reclaimers depend on kswapd or flusher threads to do the necessary work.
However, as filesystems sometimes ignore direct reclaim requests already,
it is not expected to be a serious issue.

Patch 1 disables writeback of filesystem pages from direct reclaim
	entirely. Anonymous pages are still written.

Patch 2 removes dead code in lumpy reclaim as it is no longer able
	to synchronously write pages. This hurts lumpy reclaim but
	there is an expectation that compaction is used for hugepage
	allocations these days and lumpy reclaim's days are numbered.

Patches 3-4 add warnings to XFS and ext4 if called from
	direct reclaim. With patch 1, this "never happens" and is
	intended to catch regressions in this logic in the future.

Patch 5 disables writeback of filesystem pages from kswapd unless
	the priority is raised to the point where kswapd is considered
	to be in trouble.

Patch 6 throttles reclaimers if too many dirty pages are being
	encountered and the zones or backing devices are congested.

Patch 7 invalidates dirty pages found at the end of the LRU so they
	are reclaimed quickly after being written back rather than
	waiting for a reclaimer to find them

I consider this series to be orthogonal to the writeback work but it is
worth noting that the writeback work affects the viability of patch 8 in
particular.

I tested this on ext4 and xfs using fs_mark, a simple writeback test based
on dd and a micro benchmark that does a streaming write to a large mapping
(exercises use-once LRU logic) followed by streaming writes to a mix of
anonymous and file-backed mappings.  The command line for fs_mark when
botted with 512M looked something like

./fs_mark -d  /tmp/fsmark-2676  -D  100  -N  150  -n  150  -L  25  -t  1  -S0  -s  10485760

The number of files was adjusted depending on the amount of available
memory so that the files created was about 3xRAM.  For multiple threads,
the -d switch is specified multiple times.

The test machine is x86-64 with an older generation of AMD processor with
4 cores.  The underlying storage was 4 disks configured as RAID-0 as this
was the best configuration of storage I had available.  Swap is on a
separate disk.  Dirty ratio was tuned to 40% instead of the default of
20%.

Testing was run with and without monitors to both verify that the patches
were operating as expected and that any performance gain was real and not
due to interference from monitors.

Here is a summary of results based on testing XFS.

512M1P-xfs           Files/s  mean                 32.69 ( 0.00%)     34.44 ( 5.08%)
512M1P-xfs           Elapsed Time fsmark                    51.41     48.29
512M1P-xfs           Elapsed Time simple-wb                114.09    108.61
512M1P-xfs           Elapsed Time mmap-strm                113.46    109.34
512M1P-xfs           Kswapd efficiency fsmark                 62%       63%
512M1P-xfs           Kswapd efficiency simple-wb              56%       61%
512M1P-xfs           Kswapd efficiency mmap-strm              44%       42%
512M-xfs             Files/s  mean                 30.78 ( 0.00%)     35.94 (14.36%)
512M-xfs             Elapsed Time fsmark                    56.08     48.90
512M-xfs             Elapsed Time simple-wb                112.22     98.13
512M-xfs             Elapsed Time mmap-strm                219.15    196.67
512M-xfs             Kswapd efficiency fsmark                 54%       56%
512M-xfs             Kswapd efficiency simple-wb              54%       55%
512M-xfs             Kswapd efficiency mmap-strm              45%       44%
512M-4X-xfs          Files/s  mean                 30.31 ( 0.00%)     33.33 ( 9.06%)
512M-4X-xfs          Elapsed Time fsmark                    63.26     55.88
512M-4X-xfs          Elapsed Time simple-wb                100.90     90.25
512M-4X-xfs          Elapsed Time mmap-strm                261.73    255.38
512M-4X-xfs          Kswapd efficiency fsmark                 49%       50%
512M-4X-xfs          Kswapd efficiency simple-wb              54%       56%
512M-4X-xfs          Kswapd efficiency mmap-strm              37%       36%
512M-16X-xfs         Files/s  mean                 60.89 ( 0.00%)     65.22 ( 6.64%)
512M-16X-xfs         Elapsed Time fsmark                    67.47     58.25
512M-16X-xfs         Elapsed Time simple-wb                103.22     90.89
512M-16X-xfs         Elapsed Time mmap-strm                237.09    198.82
512M-16X-xfs         Kswapd efficiency fsmark                 45%       46%
512M-16X-xfs         Kswapd efficiency simple-wb              53%       55%
512M-16X-xfs         Kswapd efficiency mmap-strm              33%       33%

Up until 512-4X, the FSmark improvements were statistically significant.
For the 4X and 16X tests the results were within standard deviations but
just barely.  The time to completion for all tests is improved which is an
important result.  In general, kswapd efficiency is not affected by
skipping dirty pages.

1024M1P-xfs          Files/s  mean                 39.09 ( 0.00%)     41.15 ( 5.01%)
1024M1P-xfs          Elapsed Time fsmark                    84.14     80.41
1024M1P-xfs          Elapsed Time simple-wb                210.77    184.78
1024M1P-xfs          Elapsed Time mmap-strm                162.00    160.34
1024M1P-xfs          Kswapd efficiency fsmark                 69%       75%
1024M1P-xfs          Kswapd efficiency simple-wb              71%       77%
1024M1P-xfs          Kswapd efficiency mmap-strm              43%       44%
1024M-xfs            Files/s  mean                 35.45 ( 0.00%)     37.00 ( 4.19%)
1024M-xfs            Elapsed Time fsmark                    94.59     91.00
1024M-xfs            Elapsed Time simple-wb                229.84    195.08
1024M-xfs            Elapsed Time mmap-strm                405.38    440.29
1024M-xfs            Kswapd efficiency fsmark                 79%       71%
1024M-xfs            Kswapd efficiency simple-wb              74%       74%
1024M-xfs            Kswapd efficiency mmap-strm              39%       42%
1024M-4X-xfs         Files/s  mean                 32.63 ( 0.00%)     35.05 ( 6.90%)
1024M-4X-xfs         Elapsed Time fsmark                   103.33     97.74
1024M-4X-xfs         Elapsed Time simple-wb                204.48    178.57
1024M-4X-xfs         Elapsed Time mmap-strm                528.38    511.88
1024M-4X-xfs         Kswapd efficiency fsmark                 81%       70%
1024M-4X-xfs         Kswapd efficiency simple-wb              73%       72%
1024M-4X-xfs         Kswapd efficiency mmap-strm              39%       38%
1024M-16X-xfs        Files/s  mean                 42.65 ( 0.00%)     42.97 ( 0.74%)
1024M-16X-xfs        Elapsed Time fsmark                   103.11     99.11
1024M-16X-xfs        Elapsed Time simple-wb                200.83    178.24
1024M-16X-xfs        Elapsed Time mmap-strm                397.35    459.82
1024M-16X-xfs        Kswapd efficiency fsmark                 84%       69%
1024M-16X-xfs        Kswapd efficiency simple-wb              74%       73%
1024M-16X-xfs        Kswapd efficiency mmap-strm              39%       40%

All FSMark tests up to 16X had statistically significant improvements.
For the most part, tests are completing faster with the exception of the
streaming writes to a mixture of anonymous and file-backed mappings which
were slower in two cases

In the cases where the mmap-strm tests were slower, there was more
swapping due to dirty pages being skipped.  The number of additional pages
swapped is almost identical to the fewer number of pages written from
reclaim.  In other words, roughly the same number of pages were reclaimed
but swapping was slower.  As the test is a bit unrealistic and stresses
memory heavily, the small shift is acceptable.

4608M1P-xfs          Files/s  mean                 29.75 ( 0.00%)     30.96 ( 3.91%)
4608M1P-xfs          Elapsed Time fsmark                   512.01    492.15
4608M1P-xfs          Elapsed Time simple-wb                618.18    566.24
4608M1P-xfs          Elapsed Time mmap-strm                488.05    465.07
4608M1P-xfs          Kswapd efficiency fsmark                 93%       86%
4608M1P-xfs          Kswapd efficiency simple-wb              88%       84%
4608M1P-xfs          Kswapd efficiency mmap-strm              46%       45%
4608M-xfs            Files/s  mean                 27.60 ( 0.00%)     28.85 ( 4.33%)
4608M-xfs            Elapsed Time fsmark                   555.96    532.34
4608M-xfs            Elapsed Time simple-wb                659.72    571.85
4608M-xfs            Elapsed Time mmap-strm               1082.57   1146.38
4608M-xfs            Kswapd efficiency fsmark                 89%       91%
4608M-xfs            Kswapd efficiency simple-wb              88%       82%
4608M-xfs            Kswapd efficiency mmap-strm              48%       46%
4608M-4X-xfs         Files/s  mean                 26.00 ( 0.00%)     27.47 ( 5.35%)
4608M-4X-xfs         Elapsed Time fsmark                   592.91    564.00
4608M-4X-xfs         Elapsed Time simple-wb                616.65    575.07
4608M-4X-xfs         Elapsed Time mmap-strm               1773.02   1631.53
4608M-4X-xfs         Kswapd efficiency fsmark                 90%       94%
4608M-4X-xfs         Kswapd efficiency simple-wb              87%       82%
4608M-4X-xfs         Kswapd efficiency mmap-strm              43%       43%
4608M-16X-xfs        Files/s  mean                 26.07 ( 0.00%)     26.42 ( 1.32%)
4608M-16X-xfs        Elapsed Time fsmark                   602.69    585.78
4608M-16X-xfs        Elapsed Time simple-wb                606.60    573.81
4608M-16X-xfs        Elapsed Time mmap-strm               1549.75   1441.86
4608M-16X-xfs        Kswapd efficiency fsmark                 98%       98%
4608M-16X-xfs        Kswapd efficiency simple-wb              88%       82%
4608M-16X-xfs        Kswapd efficiency mmap-strm              44%       42%

Unlike the other tests, the fsmark results are not statistically
significant but the min and max times are both improved and for the most
part, tests completed faster.

There are other indications that this is an improvement as well.  For
example, in the vast majority of cases, there were fewer pages scanned by
direct reclaim implying in many cases that stalls due to direct reclaim
are reduced.  KSwapd is scanning more due to skipping dirty pages which is
unfortunate but the CPU usage is still acceptable

In an earlier set of tests, I used blktrace and in almost all cases
throughput throughout the entire test was higher.  However, I ended up
discarding those results as recording blktrace data was too heavy for my
liking.

On a laptop, I plugged in a USB stick and ran a similar tests of tests
using it as backing storage.  A desktop environment was running and for
the entire duration of the tests, firefox and gnome terminal were
launching and exiting to vaguely simulate a user.

1024M-xfs            Files/s  mean               0.41 ( 0.00%)        0.44 ( 6.82%)
1024M-xfs            Elapsed Time fsmark               2053.52   1641.03
1024M-xfs            Elapsed Time simple-wb            1229.53    768.05
1024M-xfs            Elapsed Time mmap-strm            4126.44   4597.03
1024M-xfs            Kswapd efficiency fsmark              84%       85%
1024M-xfs            Kswapd efficiency simple-wb           92%       81%
1024M-xfs            Kswapd efficiency mmap-strm           60%       51%
1024M-xfs            Avg wait ms fsmark                5404.53     4473.87
1024M-xfs            Avg wait ms simple-wb             2541.35     1453.54
1024M-xfs            Avg wait ms mmap-strm             3400.25     3852.53

The mmap-strm results were hurt because firefox launching had a tendency
to push the test out of memory.  On the postive side, firefox launched
marginally faster with the patches applied.  Time to completion for many
tests was faster but more importantly - the "Avg wait" time as measured by
iostat was far lower implying the system would be more responsive.  It was
also the case that "Avg wait ms" on the root filesystem was lower.  I
tested it manually and while the system felt slightly more responsive
while copying data to a USB stick, it was marginal enough that it could be
my imagination.

This patch: do not writeback filesystem pages in direct reclaim.

When kswapd is failing to keep zones above the min watermark, a process
will enter direct reclaim in the same manner kswapd does.  If a dirty page
is encountered during the scan, this page is written to backing storage
using mapping->writepage.

This causes two problems.  First, it can result in very deep call stacks,
particularly if the target storage or filesystem are complex.  Some
filesystems ignore write requests from direct reclaim as a result.  The
second is that a single-page flush is inefficient in terms of IO.  While
there is an expectation that the elevator will merge requests, this does
not always happen.  Quoting Christoph Hellwig;

	The elevator has a relatively small window it can operate on,
	and can never fix up a bad large scale writeback pattern.

This patch prevents direct reclaim writing back filesystem pages by
checking if current is kswapd.  Anonymous pages are still written to swap
as there is not the equivalent of a flusher thread for anonymous pages.
If the dirty pages cannot be written back, they are placed back on the LRU
lists.  There is now a direct dependency on dirty page balancing to
prevent too many pages in the system being dirtied which would prevent
reclaim making forward progress.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: remove dead code related to lumpy reclaim waiting on pages under writeback

Lumpy reclaim worked with two passes - the first which queued pages for IO
and the second which waited on writeback.  As direct reclaim can no longer
write pages there is some dead code.  This patch removes it but direct
reclaim will continue to wait on pages under writeback while in
synchronous reclaim mode.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: do not writeback filesystem pages in kswapd except in high priority

It is preferable that no dirty pages are dispatched for cleaning from the
page reclaim path.  At normal priorities, this patch prevents kswapd
writing pages.

However, page reclaim does have a requirement that pages be freed in a
particular zone.  If it is failing to make sufficient progress (reclaiming
< SWAP_CLUSTER_MAX at any priority priority), the priority is raised to
scan more pages.  A priority of DEF_PRIORITY - 3 is considered to be the
point where kswapd is getting into trouble reclaiming pages.  If this
priority is reached, kswapd will dispatch pages for writing.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: throttle reclaim if encountering too many dirty pages under writeback

Workloads that are allocating frequently and writing files place a large
number of dirty pages on the LRU.  With use-once logic, it is possible for
them to reach the end of the LRU quickly requiring the reclaimer to scan
more to find clean pages.  Ordinarily, processes that are dirtying memory
will get throttled by dirty balancing but this is a global heuristic and
does not take into account that LRUs are maintained on a per-zone basis.
This can lead to a situation whereby reclaim is scanning heavily, skipping
over a large number of pages under writeback and recycling them around the
LRU consuming CPU.

This patch checks how many of the number of pages isolated from the LRU
were dirty and under writeback.  If a percentage of them under writeback,
the process will be throttled if a backing device or the zone is
congested.  Note that this applies whether it is anonymous or file-backed
pages that are under writeback meaning that swapping is potentially
throttled.  This is intentional due to the fact if the swap device is
congested, scanning more pages and dispatching more IO is not going to
help matters.

The percentage that must be in writeback depends on the priority.  At
default priority, all of them must be dirty.  At DEF_PRIORITY-1, 50% of
them must be, DEF_PRIORITY-2, 25% etc.  i.e.  as pressure increases the
greater the likelihood the process will get throttled to allow the flusher
threads to make some progress.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm: vmscan: immediately reclaim end-of-LRU dirty pages when writeback completes

When direct reclaim encounters a dirty page, it gets recycled around the
LRU for another cycle.  This patch marks the page PageReclaim similar to
deactivate_page() so that the page gets reclaimed almost immediately after
the page gets cleaned.  This is to avoid reclaiming clean pages that are
younger than a dirty page encountered at the end of the LRU that might
have been something like a use-once page.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>