[PATCH 1/6] GITWEB - Load Checking

["John 'Warthog9' Hawley" <warthog9@kernel.org>]

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This changes the behavior, slightly, of gitweb so that it verifies
that the box isn't inundated with before attempting to serve gitweb.
If the box is overloaded, it basically returns a 503 server unavailable
until the load falls below the defined threshold.  This helps dramatically
if you have a box that's I/O bound, reaches a certain load and you
don't want gitweb, the I/O hog that it is, increasing the pain the
server is already undergoing.

adds $maxload configuration variable.  Default is a load of 300,
which for most cases should never be hit.

Please note this makes the assumption that /proc/loadavg exists
as there is no good way to read load averages on a great number of
platforms [READ: Windows], or that it's reasonably accurate.

Signed-off-by: John 'Warthog9' Hawley <warthog9@eaglescrag.net>
---
 gitweb/gitweb.perl |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)


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diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 7e477af..813e48f 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -221,6 +221,11 @@ our %avatar_size = (
 	'double'  => 32
 );
 
+# Used to set the maximum load that we will still respond to gitweb queries.
+# if we exceed this than we do the processing to figure out if there's a mirror
+# and redirect to it, or to just return 503 server busy
+our $maxload = 300;
+
 # You define site-wide feature defaults here; override them with
 # $GITWEB_CONFIG as necessary.
 our %feature = (
@@ -551,6 +556,25 @@ if (-e $GITWEB_CONFIG) {
 	do $GITWEB_CONFIG_SYSTEM if -e $GITWEB_CONFIG_SYSTEM;
 }
 
+# loadavg throttle
+sub get_loadavg() {
+    my $load;
+    my @loads;
+
+    open($load, '<', '/proc/loadavg') or return 0;
+    @loads = split(/\s+/, scalar <$load>);
+    close($load);
+    return $loads[0];
+}
+
+if (get_loadavg() > $maxload) {
+    print "Content-Type: text/plain\n";
+    print "Status: 503 Excessive load on server\n";
+    print "\n";
+    print "The load average on the server is too high\n";
+    exit 0;
+}
+
 # version of the core git binary
 our $git_version = qx("$GIT" --version) =~ m/git version (.*)$/ ? $1 : "unknown";
 $number_of_git_cmds++;