Yes, actually lots of (50+) clients are trying to create the same
large directory tree concurrently. So the behavior is most of the
mkdir will get -EEXISTS.
not very understand how the mkdir call from application level be
finally turned into lookup in MDS? could you please explain a bit
more ?
2017-10-23 8:44 GMT+08:00 Yan, Zheng <ukernel@xxxxxxxxx>:
> On Sun, Oct 22, 2017 at 11:27 PM, Xiaoxi Chen <superdebuger@xxxxxxxxx> wrote:
>> To add another data point, switched to ceph-fuse 12.2.0, still seeing
>> lots of lookup.
>> lookup avg 1892
>> mkdir avg 367
>> create avg 222
>> open avg 228
>>
>
> But in your test, mkdir avg was about 1.5 times of open avg. I think
> your test created millions of directories, lookups were from cache
> miss. You can try enlarging client_cache_size. But I don't think it
> will help much when active set of directory are so large.
>
>
>> 2017-10-21 2:09 GMT+08:00 Xiaoxi Chen <superdebuger@xxxxxxxxx>:
>>> @Zheng, my kernel doesn't even has c3f4688a08f. But 200fd27 ("ceph:
>>> use lookup request to revalidate dentry") is there.
>>>
>>> 2017-10-21 0:54 GMT+08:00 Xiaoxi Chen <superdebuger@xxxxxxxxx>:
>>>> Thanks, will check.
>>>>
>>>> A general question, does cephfs kernel client drop dentries/inode
>>>> cache aggressively? What I know is if MDS issue
>>>> CEPH_SESSION_RECALL_STATE, client will drop, but is there other cases
>>>> client will drop cache?
>>>>
>>>>
>>>>
>>>> 2017-10-20 16:39 GMT+08:00 Yan, Zheng <ukernel@xxxxxxxxx>:
>>>>> On Fri, Oct 20, 2017 at 3:28 PM, Xiaoxi Chen <superdebuger@xxxxxxxxx> wrote:
>>>>>> Centos 7.3, kernel version 3.10.0-514.26.2.el7.x86_64.
>>>>>>
>>>>>> I extract the logical of file creation in our workload into a
>>>>>> reproducer , like below.
>>>>>>
>>>>>> Concurrently run the reproducer in 2+ node can see a lots of lookup OP.
>>>>>> I thought the lookup is to open the directory tree so I tried to
>>>>>> pre-make most of the dirs , use ls -i trying to read the dentries and
>>>>>> cache it, then re-run the reproducer, seems nothing different..
>>>>>>
>>>>>> #include <sys/stat.h>
>>>>>> #include <fcntl.h>
>>>>>> int create_file(char * base, int count, int max, int depth)
>>>>>> {
>>>>>> int i;
>>>>>> for(i=0; i<count; i++) {
>>>>>> char dir[256];
>>>>>> int mydir = rand() % max;
>>>>>> sprintf(dir, "%s/%d", path, mydir);
>>>>>> if (depth >=1) {
>>>>>> mkdir(dir,0777);
>>>>>> create_dir(dir, count, max, depth - 1);
>>>>>> } else {
>>>>>> int fd = open(dir, O_CREAT | O_EXCL| O_WRONLY , 0666);
>>>>>> printf("opened path : %s = %d\n", path, fd);
>>>>>> close(fd);
>>>>>> }
>>>>>> }
>>>>>> }
>>>>>> int main(int argc, char argv[])
>>>>>> {
>>>>>> char path[256];
>>>>>> while(1) {
>>>>>> create_file("/import/SQL01", 1, 4 ,10);
>>>>>> }
>>>>>> }
>>>>>>
>>>>>
>>>>> still don't see this behavior on 4.13 kernel. I suspect there is
>>>>> something wrong with dentry lease. please check if your kernel
>>>>> include:
>>>>>
>>>>> commit c3f4688a08f (ceph: don't set req->r_locked_dir in ceph_d_revalidate)
>>>>> commit 5eb9f6040f3 (ceph: do a LOOKUP in d_revalidate instead of GETATTR)
>>>>>
>>>>> The first commit can cause this issue, the second one fixes it.
>>>>>
>>>>> Regards
>>>>> Yan, Zheng
>>>>>
>>>>>>
>>>>>>
>>>>>> 2017-10-20 10:55 GMT+08:00 Yan, Zheng <ukernel@xxxxxxxxx>:
>>>>>>> On Fri, Oct 20, 2017 at 12:49 AM, Xiaoxi Chen <superdebuger@xxxxxxxxx> wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> I am seeing a lot of lookup request when doing recursive mkdir.
>>>>>>>> The workload behavior is like:
>>>>>>>> mkdir DIR0
>>>>>>>> mkdir DIR0/DIR1
>>>>>>>> mkdir DIR0/DIR1/DIR2
>>>>>>>> ....
>>>>>>>> mkdir DIR0/DIR1/DIR2......./DIR7
>>>>>>>> create DIR0/DIR1/DIR2......./DIR7/FILE1
>>>>>>>>
>>>>>>>> and concurrently run on 50+ clients, the dir name in different
>>>>>>>> clients may or maynot be the same.
>>>>>>>>
>>>>>>>> from the admin socket I was seeing ~50K create requests, but
>>>>>>>> got 400K lookup requests. The lookup eat up most of the mds capability
>>>>>>>> so file create is slow.
>>>>>>>>
>>>>>>>> Where is the lookup comes from and can we have anyway to
>>>>>>>> optimize it out ?
>>>>>>>>
>>>>>>>
>>>>>>> I don't see this behavior when running following commands in 4.13
>>>>>>> kernel client and luminous version ceph-fuse. which client do you use?
>>>>>>>
>>>>>>> mkdir d1
>>>>>>> mkdir d1/d2
>>>>>>> mkdir d1/d2/d3
>>>>>>> mkdir d1/d2/d3/d4/
>>>>>>> mkdir d1/d2/d3/d4/d5
>>>>>>> touch d1/d2/d3/d4/d5/f
>>>>>>>
>>>>>>>> Xiaoxi
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