Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression?

[Pekka Enberg]

On Mon, Apr 25, 2011 at 12:17 PM, Bruno Prémont
<bonbons@xxxxxxxxxxxxxxxxx> wrote:
> On Mon, 25 April 2011 Mike Frysinger wrote:
>> On Sun, Apr 24, 2011 at 22:42, KOSAKI Motohiro wrote:
>> >> On Sun, 24 April 2011 Bruno Prémont wrote:
>> >> > On an older system I've been running Gentoo's revdep-rebuild to check
>> >> > for system linking/*.la consistency and after doing most of the work the
>> >> > system starved more or less, just complaining about stuck tasks now and
>> >> > then.
>> >> > Memory usage graph as seen from userspace showed sudden quick increase of
>> >> > memory usage though only a very few MB were swapped out (c.f. attached RRD
>> >> > graph).
>> >>
>> >> Seems I've hit it once again (though detected before system was fully
>> >> stalled by trying to reclaim memory without success).
>> >>
>> >> This time it was during simple compiling...
>> >> Gathered info below:
>> >>
>> >> /proc/meminfo:
>> >> MemTotal:         480660 kB
>> >> MemFree:           64948 kB
>> >> Buffers:           10304 kB
>> >> Cached:             6924 kB
>> >> SwapCached:         4220 kB
>> >> Active:            11100 kB
>> >> Inactive:          15732 kB
>> >> Active(anon):       4732 kB
>> >> Inactive(anon):     4876 kB
>> >> Active(file):       6368 kB
>> >> Inactive(file):    10856 kB
>> >> Unevictable:          32 kB
>> >> Mlocked:              32 kB
>> >> SwapTotal:        524284 kB
>> >> SwapFree:         456432 kB
>> >> Dirty:                80 kB
>> >> Writeback:             0 kB
>> >> AnonPages:          6268 kB
>> >> Mapped:             2604 kB
>> >> Shmem:                 4 kB
>> >> Slab:             250632 kB
>> >> SReclaimable:      51144 kB
>> >> SUnreclaim:       199488 kB   <--- look big as well...
>> >> KernelStack:      131032 kB   <--- what???
>> >
>> > KernelStack is used 8K bytes per thread. then, your system should have
>> > 16000 threads. but your ps only showed about 80 processes.
>> > Hmm... stack leak?
>>
>> i might have a similar report for 2.6.39-rc4 (seems to be working fine
>> in 2.6.38.4), but for embedded Blackfin systems running gdbserver
>> processes over and over (so lots of short lived forks)
>>
>> i wonder if you have a lot of zombies or otherwise unclaimed resources
>> ?  does `ps aux` show anything unusual ?
>
> I've not seen anything special (no big amount of threads behind my about 80
> processes, even after kernel oom-killed nearly all processes the hogged
> memory has not been freed. And no, there are no zombies around).
>
> Here it seems to happened when I run 2 intensive tasks in parallel, e.g.
> (re)emerging gimp and running revdep-rebuild -pi in another terminal.
> This produces a fork rate of about 100-300 per second.
>
> Suddenly kmalloc-128 slabs stop being freed and things degrade.
>
> Trying to trace some of the kmalloc-128 slab allocations I end up seeing
> lots of allocations like this:
>
> [ 1338.554429] TRACE kmalloc-128 alloc 0xc294ff00 inuse=30 fp=0xc294ff00
> [ 1338.554434] Pid: 1573, comm: collectd Tainted: G        W   2.6.39-rc4-jupiter-00187-g686c4cb #1
> [ 1338.554437] Call Trace:
> [ 1338.554442]  [<c10aef47>] trace+0x57/0xa0
> [ 1338.554447]  [<c10b07b3>] alloc_debug_processing+0xf3/0x140
> [ 1338.554452]  [<c10b0972>] T.999+0x172/0x1a0
> [ 1338.554455]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.554459]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.554464]  [<c10b0a52>] kmem_cache_alloc+0xb2/0x100
> [ 1338.554468]  [<c10c08b5>] ? path_put+0x15/0x20
> [ 1338.554472]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.554476]  [<c10b95d8>] get_empty_filp+0x58/0xc0
> [ 1338.554481]  [<c10c323f>] path_openat+0x1f/0x320
> [ 1338.554485]  [<c10a0a4e>] ? __access_remote_vm+0x19e/0x1d0
> [ 1338.554490]  [<c10c3620>] do_filp_open+0x30/0x80
> [ 1338.554495]  [<c10b0a30>] ? kmem_cache_alloc+0x90/0x100
> [ 1338.554500]  [<c10c16f8>] ? getname_flags+0x28/0xe0
> [ 1338.554505]  [<c10cd522>] ? alloc_fd+0x62/0xe0
> [ 1338.554509]  [<c10c1731>] ? getname_flags+0x61/0xe0
> [ 1338.554514]  [<c10b781d>] do_sys_open+0xed/0x1e0
> [ 1338.554519]  [<c10b7979>] sys_open+0x29/0x40
> [ 1338.554524]  [<c1391390>] sysenter_do_call+0x12/0x26
> [ 1338.556764] TRACE kmalloc-128 alloc 0xc294ff80 inuse=31 fp=0xc294ff80
> [ 1338.556774] Pid: 1332, comm: bash Tainted: G        W   2.6.39-rc4-jupiter-00187-g686c4cb #1
> [ 1338.556779] Call Trace:
> [ 1338.556794]  [<c10aef47>] trace+0x57/0xa0
> [ 1338.556802]  [<c10b07b3>] alloc_debug_processing+0xf3/0x140
> [ 1338.556807]  [<c10b0972>] T.999+0x172/0x1a0
> [ 1338.556812]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.556817]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.556821]  [<c10b0a52>] kmem_cache_alloc+0xb2/0x100
> [ 1338.556826]  [<c10b95d8>] ? get_empty_filp+0x58/0xc0
> [ 1338.556830]  [<c10b95d8>] get_empty_filp+0x58/0xc0
> [ 1338.556841]  [<c121fca8>] ? tty_ldisc_deref+0x8/0x10
> [ 1338.556849]  [<c10c323f>] path_openat+0x1f/0x320
> [ 1338.556857]  [<c11e2b3e>] ? fbcon_cursor+0xfe/0x180
> [ 1338.556863]  [<c10c3620>] do_filp_open+0x30/0x80
> [ 1338.556868]  [<c10b0a30>] ? kmem_cache_alloc+0x90/0x100
> [ 1338.556873]  [<c10c5e8e>] ? do_vfs_ioctl+0x7e/0x580
> [ 1338.556878]  [<c10c16f8>] ? getname_flags+0x28/0xe0
> [ 1338.556886]  [<c10cd522>] ? alloc_fd+0x62/0xe0
> [ 1338.556891]  [<c10c1731>] ? getname_flags+0x61/0xe0
> [ 1338.556898]  [<c10b781d>] do_sys_open+0xed/0x1e0
> [ 1338.556903]  [<c10b7979>] sys_open+0x29/0x40
> [ 1338.556913]  [<c1391390>] sysenter_do_call+0x12/0x26
>
> Collectd is system monitoring daemon that counts processes, memory
> usage an much more, reading lots of files under /proc every 10
> seconds.
> Maybe it opens a process related file at a racy moment and thus
> prevents the 128 slabs and kernel stacks from being released?
>
> Replaying the scenario I'm at:
> Slab:              43112 kB
> SReclaimable:      25396 kB
> SUnreclaim:        17716 kB
> KernelStack:       16432 kB
> PageTables:         1320 kB
>
> with
> kmalloc-256           55     64    256   16    1 : tunables    0    0    0 : slabdata      4      4      0
> kmalloc-128        66656  66656    128   32    1 : tunables    0    0    0 : slabdata   2083   2083      0
> kmalloc-64          3902   3904     64   64    1 : tunables    0    0    0 : slabdata     61     61      0
>
> (and compiling process tree now SIGSTOPped in order to have system
> not starve immediately so I can look around for information)
>
> If I resume one of the compiling process trees both KernelStack and
> slab (kmalloc-128) usage increase quite quickly (and seems to never
> get down anymore) - probably at same rate as processes get born (no
> matter when they end).

Looks like it might be a leak in VFS. You could try kmemleak to narrow
it down some more. See Documentation/kmemleak.txt for details.

                       Pekka
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