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Make epoll use less RAM.

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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
This commit is contained in:
Nick Mathewson 2009-09-11 18:47:35 +00:00
parent e3f89fa275
commit 85255a6397
2 changed files with 31 additions and 24 deletions
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1
ChangeLog
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@ -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 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 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 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: Changes in 2.0.2-alpha:

54
epoll.c
View File

@ -44,6 +44,7 @@
#include <string.h> #include <string.h>
#include <unistd.h> #include <unistd.h>
#include <errno.h> #include <errno.h>
#include <assert.h>
#ifdef _EVENT_HAVE_FCNTL_H #ifdef _EVENT_HAVE_FCNTL_H
#include <fcntl.h> #include <fcntl.h>
#endif #endif
@ -86,7 +87,8 @@ const struct eventop epollops = {
#define FD_CLOSEONEXEC(x) #define FD_CLOSEONEXEC(x)
#endif #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 /* 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 * values bigger than (LONG_MAX - 999ULL)/HZ. HZ in the wild can be
@ -99,23 +101,12 @@ const struct eventop epollops = {
static void * static void *
epoll_init(struct event_base *base) epoll_init(struct event_base *base)
{ {
int epfd, nfiles = NEVENT; int epfd;
struct rlimit rl;
struct epollop *epollop; struct epollop *epollop;
if (getrlimit(RLIMIT_NOFILE, &rl) == 0 && /* Initalize the kernel queue. (The size field is ignored since
rl.rlim_cur != RLIM_INFINITY) { * 2.6.8.) */
/* if ((epfd = epoll_create(32000)) == -1) {
* 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 (errno != ENOSYS) if (errno != ENOSYS)
event_warn("epoll_create"); event_warn("epoll_create");
return (NULL); return (NULL);
@ -129,12 +120,12 @@ epoll_init(struct event_base *base)
epollop->epfd = epfd; epollop->epfd = epfd;
/* Initalize fields */ /* 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) { if (epollop->events == NULL) {
mm_free(epollop); mm_free(epollop);
return (NULL); return (NULL);
} }
epollop->nevents = nfiles; epollop->nevents = INITIAL_NEVENT;
evsig_init(base); 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)); event_debug(("%s: epoll_wait reports %d", __func__, res));
assert(res < epollop->nevents);
for (i = 0; i < res; i++) { for (i = 0; i < res; i++) {
int what = events[i].events; int what = events[i].events;
short res = 0; short ev = 0;
if (what & (EPOLLHUP|EPOLLERR)) { if (what & (EPOLLHUP|EPOLLERR)) {
res = EV_READ | EV_WRITE; ev = EV_READ | EV_WRITE;
} else { } else {
if (what & EPOLLIN) if (what & EPOLLIN)
res |= EV_READ; ev |= EV_READ;
if (what & EPOLLOUT) if (what & EPOLLOUT)
res |= EV_WRITE; ev |= EV_WRITE;
} }
if (!res) if (!events)
continue; 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); return (0);