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      1 /*
      2  * Copyright (C) 2018 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      https://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17  /*
     18   * rss_hwm_reset clears the RSS high-water mark counters for all currently
     19   * running processes. It writes "5" to /proc/PID/clear_refs for every PID.
     20   *
     21   * It runs in its own process becuase dac_override capability is required
     22   * in order to write to other processes' clear_refs.
     23   *
     24   * It is invoked from a system service by flipping sys.rss_hwm_reset.on
     25   * property to "1".
     26   */
     27 
     28 #define LOG_TAG "rss_hwm_reset"
     29 
     30 #include <dirent.h>
     31 
     32 #include <string>
     33 
     34 #include <android-base/file.h>
     35 #include <android-base/stringprintf.h>
     36 #include <log/log.h>
     37 
     38 namespace {
     39 // Resets RSS HWM counter for the selected process by writing 5 to
     40 // /proc/PID/clear_refs.
     41 void reset_rss_hwm(const char* pid) {
     42     std::string clear_refs_path =
     43             ::android::base::StringPrintf("/proc/%s/clear_refs", pid);
     44     ::android::base::WriteStringToFile("5", clear_refs_path);
     45 }
     46 }
     47 
     48 // Clears RSS HWM counters for all currently running processes.
     49 int main(int /* argc */, char** /* argv[] */) {
     50     DIR* dirp = opendir("/proc");
     51     if (dirp == nullptr) {
     52         ALOGE("unable to read /proc");
     53         return 1;
     54     }
     55     struct dirent* entry;
     56     while ((entry = readdir(dirp)) != nullptr) {
     57         // Skip entries that are not directories.
     58         if (entry->d_type != DT_DIR) continue;
     59         // Skip entries that do not contain only numbers.
     60         const char* pid = entry->d_name;
     61         while (*pid) {
     62             if (*pid < '0' || *pid > '9') break;
     63             pid++;
     64         }
     65         if (*pid != 0) continue;
     66 
     67         pid = entry->d_name;
     68         reset_rss_hwm(pid);
     69     }
     70     closedir(dirp);
     71     return 0;
     72 }
     73