Use fadvise to trigger sequential reading

Nginx and other webservers use fadvise to inform the kernel of
in-order reading.  We should to the same.

Tested:
Webui loads correctly, no direct performance benefits immediately
obvious, but likely would operate better under load.

Change-Id: I4acce316c719df7df012cea8cb89237b28932c15
Signed-off-by: Ed Tanous <ed@tanous.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/http/http_body.hpp b/http/http_body.hpp
index f2ec53fec2..46070cc60f 100644
--- a/http/http_body.hpp
+++ b/http/http_body.hpp
@@ -3,6 +3,7 @@
 #include "logging.hpp"
 #include "utility.hpp"
 
+#include <fcntl.h>
 #include <unistd.h>
 
 #include <boost/beast/core/buffers_range.hpp>
@@ -139,6 +140,13 @@ class HttpBody::value_type
         {
             BMCWEB_LOG_WARNING("Failed to read file size on {}", path);
         }
+
+        int fadvise = posix_fadvise(fileHandle.native_handle(), 0, 0,
+                                    POSIX_FADV_SEQUENTIAL);
+        if (fadvise != 0)
+        {
+            BMCWEB_LOG_WARNING("Fasvise returned {} ignoring", fadvise);
+        }
         ec = {};
     }