Make epoll use less RAM.

We do this by not allocating the maximum epoll_event array for the epoll
backend at startup.  Instead, we start out accepting 32 events at a time, and
double the array's size when it seems that the OS is generating events faster
than we're requesting them.  This saves up to 374K per epoll-based
event_base.  Resolves bug 2839240.

svn:r1428

diff --git a/ChangeLog b/ChangeLog
index c4df68449a7a0b13067d58d08ade3182e517e918..afc04bd55bc1b90e0344ad64bc22acba1d8e8668 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,7 @@ Changes in 2.0.3-alpha:
  o When we send a BEV_EVENT_CONNECTED to indicate connected status, we no longer invoke the write callback as well unless we actually wrote data too.
  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 detect whether we have monotonic clock support every time a new event base is created: instead do it only once.  Patch taken from Chromium.
+ o Do not allocate the maximum event queue 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 374K per epoll-based event_base.  Resolves bug 2839240.
 
 
 Changes in 2.0.2-alpha:

diff --git a/epoll.c b/epoll.c
index b553131199ea69340b29eb10e548444058bf2010..02906d9b568b427d9a84b7069d280da68c0714f3 100644 (file)
--- a/epoll.c
+++ b/epoll.c
@@ -44,6 +44,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
+#include <assert.h>
 #ifdef _EVENT_HAVE_FCNTL_H
 #include <fcntl.h>
 #endif
@@ -86,7 +87,8 @@ const struct eventop epollops = {
 #define FD_CLOSEONEXEC(x)
 #endif
 
-#define NEVENT 32000
+#define INITIAL_NEVENT 32
+#define MAX_NEVENT 4096
 
 /* 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
@@ -99,23 +101,12 @@ const struct eventop epollops = {
 static void *
 epoll_init(struct event_base *base)
 {
-       int epfd, nfiles = NEVENT;
-       struct rlimit rl;
+       int epfd;
        struct epollop *epollop;
 
-       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) {
+       /* Initalize the kernel queue.  (The size field is ignored since
+        * 2.6.8.) */
+       if ((epfd = epoll_create(32000)) == -1) {
                if (errno != ENOSYS)
                        event_warn("epoll_create");
                return (NULL);
@@ -129,12 +120,12 @@ epoll_init(struct event_base *base)
        epollop->epfd = epfd;
 
        /* Initalize fields */
-       epollop->events = mm_malloc(nfiles * sizeof(struct epoll_event));
+       epollop->events = mm_malloc(INITIAL_NEVENT * sizeof(struct epoll_event));
        if (epollop->events == NULL) {
                mm_free(epollop);
                return (NULL);
        }
-       epollop->nevents = nfiles;
+       epollop->nevents = INITIAL_NEVENT;
 
        evsig_init(base);
 
@@ -172,24 +163,39 @@ epoll_dispatch(struct event_base *base, struct timeval *tv)
        }
 
        event_debug(("%s: epoll_wait reports %d", __func__, res));
+       assert(res < epollop->nevents);
 
        for (i = 0; i < res; i++) {
                int what = events[i].events;
-               short res = 0;
+               short ev = 0;
 
                if (what & (EPOLLHUP|EPOLLERR)) {
-                       res = EV_READ | EV_WRITE;
+                       ev = EV_READ | EV_WRITE;
                } else {
                        if (what & EPOLLIN)
-                               res |= EV_READ;
+                               ev |= EV_READ;
                        if (what & EPOLLOUT)
-                               res |= EV_WRITE;
+                               ev |= EV_WRITE;
                }
 
-               if (!res)
+               if (!events)
                        continue;
 
-               evmap_io_active(base, events[i].data.fd, res | EV_ET);
+               evmap_io_active(base, events[i].data.fd, ev | EV_ET);
+       }
+
+       if (res == epollop->nevents && epollop->nevents < MAX_NEVENT) {
+               /* 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 = mm_realloc(epollop->events,
+                   new_nevents * sizeof(struct epoll_event));
+               if (new_events) {
+                       epollop->events = new_events;
+                       epollop->nevents = new_nevents;
+               }
        }
 
        return (0);