linux-toradex.git/mm/memory.c, branch v2.6.34

mm: avoid null-pointer deref in sync_mm_rss()

2010-04-07T15:38:02+00:00

- We weren't zeroing p->rss_stat[] at fork()

- Consequently sync_mm_rss() was dereferencing tsk->mm for kernel
  threads and was oopsing.

- Make __sync_task_rss_stat() static, too.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=15648

[akpm@linux-foundation.org: remove the BUG_ON(!mm->rss)]
Reported-by: Troels Liebe Bentsen 
Signed-off-by: KAMEZAWA Hiroyuki 
"Michael S. Tsirkin" 
Cc: Andrea Arcangeli 
Cc: Rik van Riel 
Cc: Minchan Kim 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h

2010-03-30T13:02:32+00:00

percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files.  percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.

percpu.h -> slab.h dependency is about to be removed.  Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability.  As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.

  http://userweb.kernel.org/~tj/misc/slabh-sweep.py

The script does the followings.

* Scan files for gfp and slab usages and update includes such that
  only the necessary includes are there.  ie. if only gfp is used,
  gfp.h, if slab is used, slab.h.

* When the script inserts a new include, it looks at the include
  blocks and try to put the new include such that its order conforms
  to its surrounding.  It's put in the include block which contains
  core kernel includes, in the same order that the rest are ordered -
  alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
  doesn't seem to be any matching order.

* If the script can't find a place to put a new include (mostly
  because the file doesn't have fitting include block), it prints out
  an error message indicating which .h file needs to be added to the
  file.

The conversion was done in the following steps.

1. The initial automatic conversion of all .c files updated slightly
   over 4000 files, deleting around 700 includes and adding ~480 gfp.h
   and ~3000 slab.h inclusions.  The script emitted errors for ~400
   files.

2. Each error was manually checked.  Some didn't need the inclusion,
   some needed manual addition while adding it to implementation .h or
   embedding .c file was more appropriate for others.  This step added
   inclusions to around 150 files.

3. The script was run again and the output was compared to the edits
   from #2 to make sure no file was left behind.

4. Several build tests were done and a couple of problems were fixed.
   e.g. lib/decompress_*.c used malloc/free() wrappers around slab
   APIs requiring slab.h to be added manually.

5. The script was run on all .h files but without automatically
   editing them as sprinkling gfp.h and slab.h inclusions around .h
   files could easily lead to inclusion dependency hell.  Most gfp.h
   inclusion directives were ignored as stuff from gfp.h was usually
   wildly available and often used in preprocessor macros.  Each
   slab.h inclusion directive was examined and added manually as
   necessary.

6. percpu.h was updated not to include slab.h.

7. Build test were done on the following configurations and failures
   were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
   distributed build env didn't work with gcov compiles) and a few
   more options had to be turned off depending on archs to make things
   build (like ipr on powerpc/64 which failed due to missing writeq).

   * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
   * powerpc and powerpc64 SMP allmodconfig
   * sparc and sparc64 SMP allmodconfig
   * ia64 SMP allmodconfig
   * s390 SMP allmodconfig
   * alpha SMP allmodconfig
   * um on x86_64 SMP allmodconfig

8. percpu.h modifications were reverted so that it could be applied as
   a separate patch and serve as bisection point.

Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.

Signed-off-by: Tejun Heo 
Guess-its-ok-by: Christoph Lameter 
Cc: Ingo Molnar 
Cc: Lee Schermerhorn

exit: fix oops in sync_mm_rss

2010-03-24T23:31:21+00:00

In 2.6.34-rc1, removing vhost_net module causes an oops in sync_mm_rss
(called from do_exit) when workqueue is destroyed.  This does not happen
on net-next, or with vhost on top of to 2.6.33.

The issue seems to be introduced by
34e55232e59f7b19050267a05ff1226e5cd122a5 ("mm: avoid false sharing of
mm_counter) which added sync_mm_rss() that is passed task->mm, and
dereferences it without checking.  If task is a kernel thread, mm might be
NULL.  I think this might also happen e.g.  with aio.

This patch fixes the oops by calling sync_mm_rss when task->mm is set to
NULL.  I also added BUG_ON to detect any other cases where counters get
incremented while mm is NULL.

The oops I observed looks like this:

BUG: unable to handle kernel NULL pointer dereference at 00000000000002a8
IP: [] sync_mm_rss+0x33/0x6f
PGD 0
Oops: 0002 [#1] SMP
last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map
CPU 2
Modules linked in: vhost_net(-) tun bridge stp sunrpc ipv6 cpufreq_ondemand acpi_cpufreq freq_table kvm_intel kvm i5000_edac edac_core rtc_cmos bnx2 button i2c_i801 i2c_core rtc_core e1000e sg joydev ide_cd_mod serio_raw pcspkr rtc_lib cdrom virtio_net virtio_blk virtio_pci virtio_ring virtio af_packet e1000 shpchp aacraid uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode]

Pid: 2046, comm: vhost Not tainted 2.6.34-rc1-vhost #25 System Planar/IBM System x3550 -[7978B3G]-
RIP: 0010:[]  [] sync_mm_rss+0x33/0x6f
RSP: 0018:ffff8802379b7e60  EFLAGS: 00010202
RAX: 0000000000000008 RBX: ffff88023f2390c0 RCX: 0000000000000000
RDX: ffff88023f2396b0 RSI: 0000000000000000 RDI: ffff88023f2390c0
RBP: ffff8802379b7e60 R08: 0000000000000000 R09: 0000000000000000
R10: ffff88023aecfbc0 R11: 0000000000013240 R12: 0000000000000000
R13: ffffffff81051a6c R14: ffffe8ffffc0f540 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff880001e80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000000002a8 CR3: 000000023af23000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process vhost (pid: 2046, threadinfo ffff8802379b6000, task ffff88023f2390c0)
Stack:
 ffff8802379b7ee0 ffffffff81040687 ffffe8ffffc0f558 ffffffffa00a3e2d
<0> 0000000000000000 ffff88023f2390c0 ffffffff81055817 ffff8802379b7e98
<0> ffff8802379b7e98 0000000100000286 ffff8802379b7ee0 ffff88023ad47d78
Call Trace:
 [] do_exit+0x147/0x6c4
 [] ? handle_rx_net+0x0/0x17 [vhost_net]
 [] ? autoremove_wake_function+0x0/0x39
 [] ? worker_thread+0x0/0x229
 [] kthreadd+0x0/0xf2
 [] kernel_thread_helper+0x4/0x10
 [] ? kthread+0x0/0x87
 [] ? kernel_thread_helper+0x0/0x10
Code: 00 8b 87 6c 02 00 00 85 c0 74 14 48 98 f0 48 01 86 a0 02 00 00 c7 87 6c 02 00 00 00 00 00 00 8b 87 70 02 00 00 85 c0 74 14 48 98  48 01 86 a8 02 00 00 c7 87 70 02 00 00 00 00 00 00 8b 87 74
RIP  [] sync_mm_rss+0x33/0x6f
 RSP 
CR2: 00000000000002a8
---[ end trace 41603ba922beddd2 ]---
Fixing recursive fault but reboot is needed!

(note: handle_rx_net is a work item using workqueue in question).
sync_mm_rss+0x33/0x6f gave me a hint. I also tried reverting
34e55232e59f7b19050267a05ff1226e5cd122a5 and the oops goes away.

The module in question calls use_mm and later unuse_mm from a kernel
thread.  It is when this kernel thread is destroyed that the crash
happens.

Signed-off-by: Michael S. Tsirkin 
Andrea Arcangeli 
Reviewed-by: Rik van Riel 
Reviewed-by: KAMEZAWA Hiroyuki 
Reviewed-by: Minchan Kim 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: introduce dump_page() and print symbolic flag names

2010-03-12T23:52:28+00:00

- introduce dump_page() to print the page info for debugging some error
  condition.

- convert three mm users: bad_page(), print_bad_pte() and memory offline
  failure.

- print an extra field: the symbolic names of page->flags

Example dump_page() output:

[  157.521694] page:ffffea0000a7cba8 count:2 mapcount:1 mapping:ffff88001c901791 index:0x147
[  157.525570] page flags: 0x100000000100068(uptodate|lru|active|swapbacked)

Signed-off-by: Wu Fengguang 
Cc: Ingo Molnar 
Cc: Alex Chiang 
Cc: Rik van Riel 
Cc: Andi Kleen 
Cc: Mel Gorman 
Cc: Christoph Lameter 
Cc: KOSAKI Motohiro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

nommu: fix build breakage

2010-03-12T23:52:28+00:00

Commit 34e55232e59f7b19050267a05ff1226e5cd122a5 ("mm: avoid false sharing
of mm_counter") added sync_mm_rss() for syncing loosely accounted rss
counters.  It's for CONFIG_MMU but sync_mm_rss is called even in NOMMU
enviroment (kerne/exit.c, fs/exec.c).  Above commit doesn't handle it
well.

This patch changes
  SPLIT_RSS_COUNTING depends on SPLIT_PTLOCKS && CONFIG_MMU

And for avoid unnecessary function calls, sync_mm_rss changed to be inlined
noop function in header file.

Reported-by: David Howells 
Signed-off-by: KAMEZAWA Hiroyuki 
Signed-off-by: Mike Frysinger 
Signed-off-by: Michal Simek 
Signed-off-by: David Howells 
Cc: Greg Ungerer 
Cc: Geert Uytterhoeven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

rmap: move exclusively owned pages to own anon_vma in do_wp_page()

2010-03-06T19:26:26+00:00

When the parent process breaks the COW on a page, both the original which
is mapped at child and the new page which is mapped parent end up in that
same anon_vma.  Generally this won't be a problem, but for some workloads
it could preserve the O(N) rmap scanning complexity.

A simple fix is to ensure that, when a page which is mapped child gets
reused in do_wp_page, because we already are the exclusive owner, the page
gets moved to our own exclusive child's anon_vma.

Signed-off-by: Rik van Riel 
Cc: KOSAKI Motohiro 
Cc: Larry Woodman 
Cc: Lee Schermerhorn 
Reviewed-by: Minchan Kim 
Cc: Andrea Arcangeli 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: change anon_vma linking to fix multi-process server scalability issue

2010-03-06T19:26:26+00:00

The old anon_vma code can lead to scalability issues with heavily forking
workloads.  Specifically, each anon_vma will be shared between the parent
process and all its child processes.

In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes.  However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.

This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock.  This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands.  Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.

This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA.  At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated.  The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.

This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
 This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.

The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations.  This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures.  This in
turn means error handling needs to be added to the calling functions.

A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock.  To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag.  This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.

Some test results:

Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.

With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time.  The anon_vma lock contention appears to be resolved.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel 
Cc: KOSAKI Motohiro 
Cc: Larry Woodman 
Cc: Lee Schermerhorn 
Cc: Minchan Kim 
Cc: Andrea Arcangeli 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: count swap usage

2010-03-06T19:26:24+00:00

A frequent questions from users about memory management is what numbers of
swap ents are user for processes.  And this information will give some
hints to oom-killer.

Besides we can count the number of swapents per a process by scanning
/proc//smaps, this is very slow and not good for usual process
information handler which works like 'ps' or 'top'.  (ps or top is now
enough slow..)

This patch adds a counter of swapents to mm_counter and update is at each
swap events.  Information is exported via /proc//status file as

[kamezawa@bluextal memory]$ cat /proc/self/status
Name:   cat
State:  R (running)
Tgid:   2910
Pid:    2910
PPid:   2823
TracerPid:      0
Uid:    500     500     500     500
Gid:    500     500     500     500
FDSize: 256
Groups: 500
VmPeak:    82696 kB
VmSize:    82696 kB
VmLck:         0 kB
VmHWM:       432 kB
VmRSS:       432 kB
VmData:      172 kB
VmStk:        84 kB
VmExe:        48 kB
VmLib:      1568 kB
VmPTE:        40 kB
VmSwap:        0 kB <=============== this.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KAMEZAWA Hiroyuki 
Reviewed-by: Minchan Kim 
Reviewed-by: Christoph Lameter 
Cc: Lee Schermerhorn 
Cc: David Rientjes 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: avoid false sharing of mm_counter

2010-03-06T19:26:24+00:00

Considering the nature of per mm stats, it's the shared object among
threads and can be a cache-miss point in the page fault path.

This patch adds per-thread cache for mm_counter.  RSS value will be
counted into a struct in task_struct and synchronized with mm's one at
events.

Now, in this patch, the event is the number of calls to handle_mm_fault.
Per-thread value is added to mm at each 64 calls.

 rough estimation with small benchmark on parallel thread (2threads) shows
 [before]
     4.5 cache-miss/faults
 [after]
     4.0 cache-miss/faults
 Anyway, the most contended object is mmap_sem if the number of threads grows.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KAMEZAWA Hiroyuki 
Cc: Minchan Kim 
Cc: Christoph Lameter 
Cc: Lee Schermerhorn 
Cc: David Rientjes 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: clean up mm_counter

2010-03-06T19:26:23+00:00

Presently, per-mm statistics counter is defined by macro in sched.h

This patch modifies it to
  - defined in mm.h as inlinf functions
  - use array instead of macro's name creation.

This patch is for reducing patch size in future patch to modify
implementation of per-mm counter.

Signed-off-by: KAMEZAWA Hiroyuki 
Reviewed-by: Minchan Kim 
Cc: Christoph Lameter 
Cc: Lee Schermerhorn 
Cc: David Rientjes 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds