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From:   Li Zhijian <lizhijian@cn.fujitsu.com>
Subject: [kselftests] compaction_test is blocked
Organization: fnst-ulinux
To:     <linux-kselftest@vger.kernel.org>
CC:     "Li, Philip" <philip.li@intel.com>, <linux-kernel@vger.kernel.org>,
        "Li Zhijian(intel)" <zhijianx.li@intel.com>
Message-ID: <700acd92-2b0b-d2da-615e-1f228708d216@cn.fujitsu.com>
Date:   Fri, 9 Feb 2018 15:53:59 +0800
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Hi

kselftests is integrated Intel 0Day project.
Sometimes we found compaction_test is blocked for more than 1 hours until i kill it.

Try to figure out where it is running, i added some log to this case.

the test log is like:
-------------------
  [  111.750543] main: 248
  [  111.750544]-
  [ 111.750821] check_compaction: 98
  [  111.750822]-
  [  111.751102] check_compaction: 105
  [  111.751103]-
  [  111.751362] check_compaction: 111
  [  111.751363]-
  [  111.751621] check_compaction: 118
  [  111.751622]-
  [  111.751879] check_compaction: 123
  [  111.751880]-
-------------------
118         fprintf(stderr, "%s: %d\n", __func__, __LINE__);
119         lseek(fd, 0, SEEK_SET);
120
121         /* Request a large number of huge pages. The Kernel will allocate
122            as much as it can */
123         fprintf(stderr, "%s: %d\n", __func__, __LINE__);         <<<======== the last line we can catch.
124         if (write(fd, "100000", (6*sizeof(char))) != (6*sizeof(char))) {        <<<<============ blocking position
125                 perror("Failed to write 100000 to /proc/sys/vm/nr_hugepages\n");
126                 goto close_fd;
127         }
128
129         lseek(fd, 0, SEEK_SET);
130
131         fprintf(stderr, "%s: %d\n", __func__, __LINE__);
132         if (read(fd, nr_hugepages, sizeof(nr_hugepages)) <= 0) {
133                 perror("Failed to re-read from /proc/sys/vm/nr_hugepages\n");
134                 goto close_fd;
135         }
-------------------

According to above log and code, it most likely it is blocking at the writing operation.

my environment is like:
OS: debian
kernel: v4.15
model: Ivytown Ivy Bridge-EP
nr_cpu: 48
memory: 64G


NOTE: 0Day can reproduce this issue in 20% on 0Day.

Anybody can help have a look?

Thanks
Zhjian