Message-ID: <h2h28c262361004070139r7a729959od486bb2a022afd4b@mail.gmail.com>
Date:	Wed, 7 Apr 2010 17:39:53 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andreas Mohr <andi@...as.de>, Jens Axboe <axboe@...nel.dk>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 32GB SSD on USB1.1 P3/700 == ___HELL___ (2.6.34-rc3)

On Wed, Apr 7, 2010 at 4:00 PM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> Andreas,
>
> On Mon, Apr 05, 2010 at 06:53:20PM +0800, Andreas Mohr wrote:
>> On Mon, Apr 05, 2010 at 12:13:49AM +0200, Andreas Mohr wrote:
>> > Having an attempt at writing a 300M /dev/zero file to the SSD's filesystem
>> > was even worse (again tons of unresponsiveness), combined with multiple
>> > OOM conditions flying by (I/O to the main HDD was minimal, its LED was
>> > almost always _off_, yet everything stuck to an absolute standstill).
>> >
>> > Clearly there's a very, very important limiter somewhere in bio layer
>> > missing or broken, a 300M dd /dev/zero should never manage to put
>> > such an onerous penalty on a system, IMHO.
>>
>> Seems this issue is a variation of the usual "ext3 sync" problem,
>> but in overly critical and unexpected ways (full lockup of almost everything,
>> and multiple OOMs).
>>
>> I retried writing the 300M file with a freshly booted system, and there
>> were _no_ suspicious issues to be observed (free memory went all down to
>> 5M, not too problematic), well, that is, until I launched Firefox
>> (the famous sync-happy beast).
>> After Firefox startup, I had these long freezes again when trying to
>> do transfers with the _UNRELATED_ main HDD of the system
>> (plus some OOMs, again)
>>
>> Setup: USB SSD ext4 non-journal, system HDD ext3, SSD unused except for
>> this one ext4 partition (no swap partition activated there).
>>
>> Of course I can understand and tolerate the existing "ext3 sync" issue,
>> but what's special about this case is that large numbers of bio to
>> a _separate_ _non_-ext3 device seem to put so much memory and I/O pressure
>> on a system that the existing _lightly_ loaded ext3 device gets completely
>> stuck for much longer than I'd usually naively expect an ext3 sync to an isolated
>> device to take - not to mention the OOMs (which are probably causing
>> swap partition handling on the main HDD to contribute to the contention).
>>
>> IOW, we seem to still have too much ugly lock contention interaction
>> between expectedly isolated parts of the system.
>>
>> OTOH the main problem likely still is overly large pressure induced by a
>> thoroughly unthrottled dd 300M, resulting in sync-challenged ext3 and swap
>> activity (this time on the same device!) to break completely, and also OOMs to occur.
>>
>> Probably overly global ext3 sync handling manages to grab a couple
>> more global system locks (bdi, swapping, page handling, ...)
>> before being contended, causing other, non-ext3-challenged
>> parts of the system (e.g. the swap partition on the _same_ device)
>> to not make any progress in the meantime.
>>
>> per-bdi writeback patches (see
>> http://www.serverphorums.com/read.php?12,32355,33238,page=2 ) might
>> have handled a related issue.
>>
>>
>> Following is a SysRq-W trace (plus OOM traces) at a problematic moment during 300M copy
>> after firefox - and thus sync invocation - launch (there's a backtrace of an "ls" that
>> got stuck for perhaps half a minute on the main, _unaffected_, ext3
>> HDD - and almost all other traces here are ext3-bound as well).
>>
>>
>> SysRq : HELP : loglevel(0-9) reBoot Crash show-all-locks(D) terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) thaw-filesystems(J) saK show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount show-blocked-tasks(W)
>> ata1: clearing spurious IRQ
>> ata1: clearing spurious IRQ
>> Xorg invoked oom-killer: gfp_mask=0xd0, order=0, oom_adj=0
>
> This is GFP_KERNEL.
>
>> Pid: 2924, comm: Xorg Tainted: G        W  2.6.34-rc3 #8
>> Call Trace:
>>  [<c105d881>] T.382+0x44/0x110
>>  [<c105d978>] T.381+0x2b/0xe1
>>  [<c105db2e>] __out_of_memory+0x100/0x112
>>  [<c105dbb4>] out_of_memory+0x74/0x9c
>>  [<c105fd41>] __alloc_pages_nodemask+0x3c5/0x493
>>  [<c105fe1e>] __get_free_pages+0xf/0x2c
>>  [<c1086400>] __pollwait+0x4c/0xa4
>>  [<c120130e>] unix_poll+0x1a/0x93
>>  [<c11a6a77>] sock_poll+0x12/0x15
>>  [<c1085d21>] do_select+0x336/0x53a
>>  [<c10ec5c4>] ? cfq_set_request+0x1d8/0x2ec
>>  [<c10863b4>] ? __pollwait+0x0/0xa4
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c1086458>] ? pollwake+0x0/0x60
>>  [<c10f46c9>] ? _copy_from_user+0x42/0x127
>>  [<c10860cc>] core_sys_select+0x1a7/0x291
>>  [<c1214063>] ? _raw_spin_unlock_irq+0x1d/0x21
>>  [<c1026b7f>] ? do_setitimer+0x160/0x18c
>>  [<c103b066>] ? ktime_get_ts+0xba/0xc4
>>  [<c108635e>] sys_select+0x68/0x84
>>  [<c1002690>] sysenter_do_call+0x12/0x31
>> Mem-Info:
>> DMA per-cpu:
>> CPU    0: hi:    0, btch:   1 usd:   0
>> Normal per-cpu:
>> CPU    0: hi:  186, btch:  31 usd:  46
>> active_anon:34886 inactive_anon:41460 isolated_anon:1
>>  active_file:13576 inactive_file:27884 isolated_file:65
>>  unevictable:0 dirty:4788 writeback:5675 unstable:0
>>  free:1198 slab_reclaimable:1952 slab_unreclaimable:2594
>>  mapped:10152 shmem:56 pagetables:742 bounce:0
>> DMA free:2052kB min:84kB low:104kB high:124kB active_anon:940kB inactive_anon:3876kB active_file:212kB inactive_file:8224kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15804kB mlocked:0kB dirty:3448kB writeback:752kB mapped:80kB shmem:0kB slab_reclaimable:160kB slab_unreclaimable:124kB kernel_stack:40kB pagetables:48kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:20096 all_unreclaimable? yes
>> lowmem_reserve[]: 0 492 492
>> Normal free:2740kB min:2792kB low:3488kB high:4188kB active_anon:138604kB inactive_anon:161964kB active_file:54092kB inactive_file:103312kB unevictable:0kB isolated(anon):4kB isolated(file):260kB present:503848kB mlocked:0kB dirty:15704kB writeback:21948kB mapped:40528kB shmem:224kB slab_reclaimable:7648kB slab_unreclaimable:10252kB kernel_stack:1632kB pagetables:2920kB unstable:0kB bounce:0kB writeback_tmp:0kB pages_scanned:73056 all_unreclaimable? no
>> lowmem_reserve[]: 0 0 0
>> DMA: 513*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 2052kB
>> Normal: 685*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 2740kB
>> 56122 total pagecache pages
>> 14542 pages in swap cache
>> Swap cache stats: add 36404, delete 21862, find 8669/10118
>> Free swap  = 671696kB
>> Total swap = 755048kB
>> 131034 pages RAM
>> 3214 pages reserved
>> 94233 pages shared
>> 80751 pages non-shared
>> Out of memory: kill process 3462 (kdeinit4) score 95144 or a child
>
> shmem=56 is ignorable, and
> active_file+inactive_file=13576+27884=41460 < 56122 total pagecache pages.
>
> Where are the 14606 file pages gone?

swapcache?


-- 
Kind regards,
Minchan Kim
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