Hello!

On Wed, Apr 06, 2011 at 05:55:58PM +0200, Srebrenko Šehić wrote:

> 2011/4/5 Srebrenko Šehić <ssehic@gmail.com>:
>
> > I will try to get a gdb trace of running wild process.
>
> Some more info about this problem. I had cache manager in a spinlock
> using 100% CPU. I did a ktrace (this is on OpenBSD 4.8/amd64 running
> 0.8.50) and here is the output (edited for brevity):
>
> # ps auxww | grep 28055 | grep -v grep
> _proxy 28055 99.1 1.9 646012 39096 ?? R/0 2:28PM 75:07.06
> nginx: cache manager process (nginx)
>
> # kdump -R | head -50
> 28055 nginx 1302104178.942729 EMUL "native"
> 28055 nginx 0.000051 RET gettimeofday 0
> 28055 nginx 0.000031 CALL gettimeofday(0x7f7ffffea2a0,0)
> 28055 nginx 0.000011 RET gettimeofday 0

No, this isn't not in spinlock. While looping in spinlock nginx
only runs and calls sched_yeild(), nothing more. This is another
problem.

[...]

> I also found out that setting "proxy_cache_path .... max_size=10k" (a
> ridiculously small number) while there is traffic on the virtualhost
> triggers the problem even *without* nginx receiving a SIGHUP.

I was able to reproduce the problem. With max_size=0 it starts
hogging cpu right on startup.

Try the attached patch. It's against 0.9.7, but probably will
apply cleanly or with minor modifications to 0.8.* as well.

Maxim Dounin
# HG changeset patch
# User Maxim Dounin <mdounin@mdounin.ru>
# Date 1302113238 -14400
# Node ID de5be49305c6ae5c71ffbed522d9feb383e2d81a
# Parent c4e0de226b0b4292c120f85ef3d509df1d6db47f
Cache: fix cpu hog in cache manager.

If cache manager can't make any progress (e.g. due to locked entries, or
max_size being effectively set to 0, or no memory) it was looping in
ngx_http_file_cache_manager() consuming cpu. Make sure to loop only if
some progress was made.

diff --git a/src/http/ngx_http_file_cache.c b/src/http/ngx_http_file_cache.c
--- a/src/http/ngx_http_file_cache.c
+++ b/src/http/ngx_http_file_cache.c
@@ -1027,6 +1027,7 @@ ngx_http_file_cache_forced_expire(ngx_ht

if (fcn->count == 0) {
ngx_http_file_cache_delete(cache, q, name);
+ wait = 0;

} else {
if (--tries) {
@@ -1191,7 +1192,7 @@ ngx_http_file_cache_manager(void *data)
ngx_http_file_cache_t *cache = data;

off_t size;
- time_t next;
+ time_t next, wait;

next = ngx_http_file_cache_expire(cache);

@@ -1212,7 +1213,11 @@ ngx_http_file_cache_manager(void *data)
return next;
}

- next = ngx_http_file_cache_forced_expire(cache);
+ wait = ngx_http_file_cache_forced_expire(cache);
+
+ if (wait > 0) {
+ return wait;
+ }

if (ngx_http_file_cache_manager_sleep(cache) != NGX_OK) {
return next;
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