On Thu, Apr 2, 2009 at 10:44 AM, Ying Han <yinghan@xxxxxxxxxx> wrote:
> On Thu, Apr 2, 2009 at 8:51 AM, Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
>> On Thursday 02 April 2009 22:34:01 Jan Kara wrote:
>>> On Thu 02-04-09 22:24:29, Nick Piggin wrote:
>>> > On Thursday 02 April 2009 09:36:13 Ying Han wrote:
>>> > > Hi Jan:
>>> > > I feel that the problem you saw is kind of differnt than mine. As
>>> > > you mentioned that you saw the PageError() message, which i don't see
>>> > > it on my system. I tried you patch(based on 2.6.21) on my system and
>>> > > it runs ok for 2 days, Still, since i don't see the same error message
>>> > > as you saw, i am not convineced this is the root cause at least for
>>> > > our problem. I am still looking into it.
>>> > > So, are you seeing the PageError() every time the problem happened?
>>> >
>>> > So I asked if you could test with my workaround of taking truncate_mutex
>>> > at the start of ext2_get_blocks, and report back. I never heard of any
>>> > response after that.
>>> >
>>> > To reiterate: I was able to reproduce a problem with ext2 (I was testing
>>> > on brd to get IO rates high enough to reproduce it quite frequently).
>>> > I think I narrowed the problem down to block allocation or inode block
>>> > tree corruption because I was unable to reproduce it with that hack in
>>> > place.
>>> Nick, what load did you use for reproduction? I'll try to reproduce it
>>> here so that I can debug ext2...
>>
>> OK, I set up the filesystem like this:
>>
>> modprobe rd rd_size=$[3*1024*1024] #almost fill memory so we reclaim buffers
>> dd if=/dev/zero of=/dev/ram0 bs=4k #prefill brd so we don't get alloc deadlock
>> mkfs.ext2 -b1024 /dev/ram0 #1K buffers
>>
>> Test is basically unmodified except I use 64MB files, and start 8 of them
>> at once to (8 core system, so improve chances of hitting the bug). Although I
>> do see it with only 1 running it takes longer to trigger.
>>
>> I also run a loop doing 'sync ; echo 3 > /proc/sys/vm/drop_caches' but I don't
>> know if that really helps speed up reproducing it. It is quite random to hit,
>> but I was able to hit it IIRC in under a minute with that setup.
>>
>
> Here is how i reproduce it:
> Filesystem is ext2 with blocksize 4096
> Fill up the ram with 95% anon memory and mlockall ( put enough memory
> pressure which will trigger page reclaim and background writeout)
> Run one thread of the test program
>
> and i will see "bad pages" within few minutes.
And here is the "top" and stdout while it is getting "bad pages"
top
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3487 root 20 0 52616 50m 284 R 95 0.3 3:58.85 usemem
3810 root 20 0 129m 99m 99m D 41 0.6 0:01.87 ftruncate_mmap
261 root 15 -5 0 0 0 D 4 0.0 0:31.08 kswapd0
262 root 15 -5 0 0 0 D 3 0.0 0:10.26 kswapd1
stdout:
while true; do
./ftruncate_mmap;
done
Running 852 bad page
Running 315 bad page
Running 999 bad page
Running 482 bad page
Running 24 bad page
--Ying
>
> --Ying
>
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