diff --git a/ChangeLog b/ChangeLog
index c6623763..2ddc2b36 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,8 @@ What's new in version 1.0.3
 
 * Performance improvements
   (thanks to Jann Horn)
+* Further performance improvements due to conditional parsing
+  of IO data depending on selected fields.
 
 What's new in version 1.0.2
 
diff --git a/ColumnsPanel.c b/ColumnsPanel.c
index 639d5e6d..f4eed99e 100644
--- a/ColumnsPanel.c
+++ b/ColumnsPanel.c
@@ -122,11 +122,14 @@ void ColumnsPanel_update(Panel* super) {
    // FIXME: this is crappily inefficient
    free(this->settings->pl->fields);
    this->settings->pl->fields = (ProcessField*) malloc(sizeof(ProcessField) * (size+1));
+   this->settings->pl->flags = 0;
    for (int i = 0; i < size; i++) {
       char* text = ((ListItem*) Panel_get(super, i))->value;
           int j = ColumnsPanel_fieldNameToIndex(text);
-          if (j > 0)
+          if (j > 0) {
              this->settings->pl->fields[i] = j;
+             this->settings->pl->flags |= Process_fieldFlags[j];
+          }
    }
    this->settings->pl->fields[size] = 0;
 }
diff --git a/Process.c b/Process.c
index af56b704..6765be7a 100644
--- a/Process.c
+++ b/Process.c
@@ -45,6 +45,12 @@ in the source distribution for its full text.
 #include "IOPriority.h"
 #include <sys/types.h>
 
+#define PROCESS_FLAG_IO 1
+#define PROCESS_FLAG_IOPRIO 2
+#define PROCESS_FLAG_OPENVZ 4
+#define PROCESS_FLAG_VSERVER 8
+#define PROCESS_FLAG_CGROUP 16
+
 #ifndef Process_isKernelThread
 #define Process_isKernelThread(_process) (_process->pgrp == 0)
 #endif
@@ -201,6 +207,31 @@ const char *Process_fieldNames[] = {
 "*** report bug! ***"
 };
 
+const int Process_fieldFlags[] = {
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0, 0, 0, 0,
+   0, 0, 0, 0,
+#ifdef HAVE_OPENVZ
+   PROCESS_FLAG_OPENVZ, PROCESS_FLAG_OPENVZ,
+#endif
+#ifdef HAVE_VSERVER
+   PROCESS_FLAG_VSERVER,
+#endif
+#ifdef HAVE_TASKSTATS
+   PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, 
+   PROCESS_FLAG_IO, PROCESS_FLAG_IO, PROCESS_FLAG_IO, 
+#endif
+#ifdef HAVE_CGROUP
+   PROCESS_FLAG_CGROUP,
+#endif
+   PROCESS_FLAG_IOPRIO
+};
+
 const char *Process_fieldTitles[] = {
    "", "    PID ", "Command ", "S ", "   PPID ", "   PGRP ", "   SESN ",
    "  TTY ", "  TPGID ", "- ", "- ", "- ", "- ", "- ",
diff --git a/Process.h b/Process.h
index c875d86e..a24c7c04 100644
--- a/Process.h
+++ b/Process.h
@@ -24,6 +24,12 @@ in the source distribution for its full text.
 #include "IOPriority.h"
 #include <sys/types.h>
 
+#define PROCESS_FLAG_IO 1
+#define PROCESS_FLAG_IOPRIO 2
+#define PROCESS_FLAG_OPENVZ 4
+#define PROCESS_FLAG_VSERVER 8
+#define PROCESS_FLAG_CGROUP 16
+
 #ifndef Process_isKernelThread
 #define Process_isKernelThread(_process) (_process->pgrp == 0)
 #endif
@@ -155,6 +161,8 @@ typedef struct Process_ {
 
 extern const char *Process_fieldNames[];
 
+extern const int Process_fieldFlags[];
+
 extern const char *Process_fieldTitles[];
 
 
diff --git a/ProcessList.c b/ProcessList.c
index ca96b883..ce1319a3 100644
--- a/ProcessList.c
+++ b/ProcessList.c
@@ -133,6 +133,7 @@ typedef struct ProcessList_ {
    unsigned long long int usedSwap;
    unsigned long long int freeSwap;
 
+   int flags;
    ProcessField* fields;
    ProcessField sortKey;
    int direction;
@@ -235,8 +236,10 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* pidWhiteList) {
    this->fields = calloc(sizeof(ProcessField), LAST_PROCESSFIELD+1);
    // TODO: turn 'fields' into a Vector,
    // (and ProcessFields into proper objects).
+   this->flags = 0;
    for (int i = 0; defaultHeaders[i]; i++) {
       this->fields[i] = defaultHeaders[i];
+      this->fields[i] |= Process_fieldFlags[defaultHeaders[i]];
    }
    this->sortKey = PERCENT_CPU;
    this->direction = 1;
@@ -738,7 +741,8 @@ static bool ProcessList_processEntries(ProcessList* this, const char* dirname, P
       ProcessList_processEntries(this, subdirname, process, period, tv);
 
       #ifdef HAVE_TASKSTATS
-      ProcessList_readIoFile(process, dirname, name, now);
+      if (this->flags & PROCESS_FLAG_IO)
+         ProcessList_readIoFile(process, dirname, name, now);
       #endif
 
       if (! ProcessList_readStatmFile(process, dirname, name))
@@ -750,7 +754,8 @@ static bool ProcessList_processEntries(ProcessList* this, const char* dirname, P
       unsigned long long int lasttimes = (process->utime + process->stime);
       if (! ProcessList_readStatFile(process, dirname, name, command))
          goto errorReadingProcess;
-      Process_updateIOPriority(process);
+      if (this->flags & PROCESS_FLAG_IOPRIO)
+         Process_updateIOPriority(process);
       float percent_cpu = (process->utime + process->stime - lasttimes) / period * 100.0;
       process->percent_cpu = MAX(MIN(percent_cpu, cpus*100.0), 0.0);
       if (isnan(process->percent_cpu)) process->percent_cpu = 0.0;
@@ -764,15 +769,18 @@ static bool ProcessList_processEntries(ProcessList* this, const char* dirname, P
          process->user = UsersTable_getRef(this->usersTable, process->st_uid);
 
          #ifdef HAVE_OPENVZ
-         ProcessList_readOpenVZData(process, dirname, name);
+         if (this->flags & PROCESS_FLAG_OPENVZ)
+            ProcessList_readOpenVZData(process, dirname, name);
          #endif
 
          #ifdef HAVE_CGROUP
-         ProcessList_readCGroupFile(process, dirname, name);
+         if (this->flags & PROCESS_FLAG_CGROUP)
+            ProcessList_readCGroupFile(process, dirname, name);
          #endif
          
          #ifdef HAVE_VSERVER
-         ProcessList_readVServerData(process, dirname, name);
+         if (this->flags & PROCESS_FLAG_VSERVER)
+            ProcessList_readVServerData(process, dirname, name);
          #endif
          
          if (! ProcessList_readCmdlineFile(process, dirname, name))
diff --git a/ProcessList.h b/ProcessList.h
index 95d32b7c..af202c87 100644
--- a/ProcessList.h
+++ b/ProcessList.h
@@ -113,6 +113,7 @@ typedef struct ProcessList_ {
    unsigned long long int usedSwap;
    unsigned long long int freeSwap;
 
+   int flags;
    ProcessField* fields;
    ProcessField sortKey;
    int direction;
diff --git a/Settings.c b/Settings.c
index fd200a7c..46b3a971 100644
--- a/Settings.c
+++ b/Settings.c
@@ -82,11 +82,13 @@ static bool Settings_read(Settings* this, char* fileName, int cpuCount) {
          char** ids = String_split(trim, ' ', &nIds);
          free(trim);
          int i, j;
+         this->pl->flags = 0;
          for (j = 0, i = 0; i < LAST_PROCESSFIELD && ids[i]; i++) {
             // This "+1" is for compatibility with the older enum format.
             int id = atoi(ids[i]) + 1;
             if (id > 0 && id < LAST_PROCESSFIELD) {
                this->pl->fields[j] = id;
+               this->pl->flags |= Process_fieldFlags[id];
                j++;
             }
          }