From 1bf18e5a065d49e9372629f17e7a714bcef78aff Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Fri, 11 Sep 2009 18:55:12 +0000
Subject: [PATCH] Backport epoll memory fix for bug 2839240

svn:r1430
---
 ChangeLog |  2 ++
 epoll.c   | 44 ++++++++++++++++++++++++--------------------
 2 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 68c95f5f..08575030 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 Changes in 1.4.13-stable:
  o If the kernel tells us that there are a negative number of bytes to read from a socket, do not believe it.  Fixes bug 2841177; found by Alexander Pronchenkov.
+ o Do not allocate the maximum event queue and fd array for the epoll backend at startup.  Instead, start out accepting 32 events at a time, and double the queue's size when it seems that the OS is generating events faster than we're requesting them.  Saves up to 512K per epoll-based event_base.  Resolves bug 2839240.
+
 
 Changes in 1.4.12-stable:
  o Try to contain degree of failure when running on a win32 version so heavily firewalled that we can't fake a socketpair.
diff --git a/epoll.c b/epoll.c
index b479b9c0..883f0d6b 100644
--- a/epoll.c
+++ b/epoll.c
@@ -94,8 +94,6 @@ const struct eventop epollops = {
 #define FD_CLOSEONEXEC(x)
 #endif
 
-#define NEVENT	32000
-
 /* On Linux kernels at least up to 2.6.24.4, epoll can't handle timeout
  * values bigger than (LONG_MAX - 999ULL)/HZ.  HZ in the wild can be
  * as big as 1000, and LONG_MAX can be as small as (1<<31)-1, so the
@@ -104,30 +102,22 @@ const struct eventop epollops = {
  */
 #define MAX_EPOLL_TIMEOUT_MSEC (35*60*1000)
 
+#define INITIAL_NFILES 32
+#define INITIAL_NEVENTS 32
+#define MAX_NEVENTS 4096
+
 static void *
 epoll_init(struct event_base *base)
 {
-	int epfd, nfiles = NEVENT;
-	struct rlimit rl;
+	int epfd;
 	struct epollop *epollop;
 
 	/* Disable epollueue when this environment variable is set */
 	if (getenv("EVENT_NOEPOLL"))
 		return (NULL);
 
-	if (getrlimit(RLIMIT_NOFILE, &rl) == 0 &&
-	    rl.rlim_cur != RLIM_INFINITY) {
-		/*
-		 * Solaris is somewhat retarded - it's important to drop
-		 * backwards compatibility when making changes.  So, don't
-		 * dare to put rl.rlim_cur here.
-		 */
-		nfiles = rl.rlim_cur - 1;
-	}
-
 	/* Initalize the kernel queue */
-
-	if ((epfd = epoll_create(nfiles)) == -1) {
+	if ((epfd = epoll_create(32000)) == -1) {
 		if (errno != ENOSYS)
 			event_warn("epoll_create");
 		return (NULL);
@@ -141,20 +131,20 @@ epoll_init(struct event_base *base)
 	epollop->epfd = epfd;
 
 	/* Initalize fields */
-	epollop->events = malloc(nfiles * sizeof(struct epoll_event));
+	epollop->events = malloc(INITIAL_NEVENTS * sizeof(struct epoll_event));
 	if (epollop->events == NULL) {
 		free(epollop);
 		return (NULL);
 	}
-	epollop->nevents = nfiles;
+	epollop->nevents = INITIAL_NEVENTS;
 
-	epollop->fds = calloc(nfiles, sizeof(struct evepoll));
+	epollop->fds = calloc(INITIAL_NFILES, sizeof(struct evepoll));
 	if (epollop->fds == NULL) {
 		free(epollop->events);
 		free(epollop);
 		return (NULL);
 	}
-	epollop->nfds = nfiles;
+	epollop->nfds = INITIAL_NFILES;
 
 	evsignal_init(base);
 
@@ -252,6 +242,20 @@ epoll_dispatch(struct event_base *base, void *arg, struct timeval *tv)
 			event_active(evwrite, EV_WRITE, 1);
 	}
 
+	if (res == epollop->nevents && epollop->nevents < MAX_NEVENTS) {
+		/* We used all of the event space this time.  We should
+		   be ready for more events next time. */
+		int new_nevents = epollop->nevents * 2;
+		struct epoll_event *new_events;
+
+		new_events = realloc(epollop->events,
+		    new_nevents * sizeof(struct epoll_event));
+		if (new_events) {
+			epollop->events = new_events;
+			epollop->nevents = new_nevents;
+		}
+	}
+
 	return (0);
 }