cros: Remove unused low memory margin code from sandbox and zygote

sandbox/linux/suid/process_util_linux.c

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The following is the C version of code from base/process_utils_linux.cc.
 // We shouldn't link against C++ code in a setuid binary.
 
 #define _GNU_SOURCE  // needed for O_DIRECTORY
 
 #include "process_util.h"
 
 #include <fcntl.h>
 #include <inttypes.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
 // Ranges for the current (oom_score_adj) and previous (oom_adj)
 // flavors of OOM score.
 static const int kMaxOomScore = 1000;
 static const int kMaxOldOomScore = 15;
 
-// Kernel pseudo-file that allows setting of the low memory margin.
-static const char kLowMemMarginFile[] =
-    "/sys/kernel/mm/chromeos-low_mem/margin";
-
 // NOTE: This is not the only version of this function in the source:
 // the base library (in process_util_linux.cc) also has its own C++ version.
 bool AdjustOOMScore(pid_t process, int score) {
   if (score < 0 || score > kMaxOomScore)
     return false;
 
   char oom_adj[27];  // "/proc/" + log_10(2**64) + "\0"
                      //    6     +       20     +     1         = 27
   snprintf(oom_adj, sizeof(oom_adj), "/proc/%" PRIdMAX, (intmax_t)process);
 
@@ skipping 29 matching lines @@
   close(dirfd);
 
   char buf[11];  // 0 <= |score| <= kMaxOomScore; using log_10(2**32) + 1 size
   snprintf(buf, sizeof(buf), "%d", score);
   size_t len = strlen(buf);
 
   ssize_t bytes_written = write(fd, buf, len);
   close(fd);
   return (bytes_written == len);
 }
-
-bool AdjustLowMemoryMargin(int64_t margin_mb) {
-  int file_descriptor = open(kLowMemMarginFile, O_WRONLY);
-  if (file_descriptor < 0)
-    return false;
-
-  // Only allow those values which are reasonable, to prevent mischief.
-  char value[21];
-  switch (margin_mb) {
-    case -1L:
-      snprintf(value, sizeof(value), "off");
-      break;
-    case 0L:
-    case 25L:
-    case 50L:
-    case 100L:
-    case 200L:
-      snprintf(value, sizeof(value), "%lld", (long long int)margin_mb);
-      break;
-    default:
-      return false;
-  }
-
-  bool success = (write(file_descriptor, value, strlen(value)) >= 0);
-  close(file_descriptor);
-  return success;
-}