Disable THP if enabled (#7381)

In case redis starts and find that THP is enabled ("always"), instead
of printing a log message, which might go unnoticed, redis will try to
disable it (just for the redis process).

Note: it looks like on self-bulit kernels THP is likely be set to "always" by default.

Some discuss about THP side effect on Linux:
according to http://www.antirez.com/news/84, we can see that
redis latency spikes are caused by linux kernel THP feature.
I have tested on E3-2650 v3, and found that 2M huge page costs
about 0.25ms to fix COW page fault.

Add a new config 'disable-thp', the recommended setting is 'yes',
(default) the redis tries to disable THP by prctl syscall. But
users who really want THP can set it to "no"

Thanks to Oran & Yossi for suggestions.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/latency.c b/src/latency.c
index 6148543c8..c661c5d6d 100644
--- a/src/latency.c
+++ b/src/latency.c
@@ -59,6 +59,7 @@ dictType latencyTimeSeriesDictType = {
 /* ------------------------- Utility functions ------------------------------ */
 
 #ifdef __linux__
+#include <sys/prctl.h>
 /* Returns 1 if Transparent Huge Pages support is enabled in the kernel.
  * Otherwise (or if we are unable to check) 0 is returned. */
 int THPIsEnabled(void) {
@@ -73,6 +74,21 @@ int THPIsEnabled(void) {
     fclose(fp);
     return (strstr(buf,"[always]") != NULL) ? 1 : 0;
 }
+
+/* since linux-3.5, kernel supports to set the state of the "THP disable" flag
+ * for the calling thread. PR_SET_THP_DISABLE is defined in linux/prctl.h */
+int THPDisable(void) {
+    int ret = -EINVAL;
+
+    if (!server.disable_thp)
+        return ret;
+
+#ifdef PR_SET_THP_DISABLE
+    ret = prctl(PR_SET_THP_DISABLE, 1, 0, 0, 0);
+#endif
+
+    return ret;
+}
 #endif
 
 /* Report the amount of AnonHugePages in smap, in bytes. If the return