Hey,
32-bit memcached with -m 4000 will never work. the best you can do is
probably -m 1600. 32bit applications typically can only allocate up to 2G
of ram.
memcached isn't protected from a lot of malloc failure scenarios, so what
you're doing will never work.
-m 4000 only limits the slab memory usage. there're a lot of buffers/etc
outside of that. Also the hash table, which is measured separately.
On Fri, 31 Oct 2014, Samdy Sun wrote:
> @Dormando,
> I try my best to reproduce this in my environment, but failed. This just
> happened on my servers.
>
> I use "stats" command to check the memcached if it is available or not. If
> the memcached is unavailable, we will not send request to it.
>
> This is what I feel strange when my curr_conns is "5" and memcached can't
> recover itself. I think "conn_new" call maybe fail, and it call
> "close(fd)" directly, not "conn_close()"? Such as below?
>
> 1. malloc fails when "conn_new()"
> 2. event_add fails when "conn_new()"
> 3. other case?
>
> Take notice of that I build "memcached" on 32-bit system and it runs on
> 64-bit system. Additionally, I use "-m 4000" for memcached's start.
>
> Thanks,
> Samdy Sun
>
> 在 2014年10月31日星期五UTC+8下午3时01分06秒，Dormando写道：
> Hey,
>
> How are you reproducing this? How many connections do you typically have
> open?
>
> It's really bizarre that your curr_conns is "5", but your connections
> are
> disabled? Even if there's still a race, as more connections close they
> each have an opportunity to flip the acceptor back on.
>
> Can you print what "stats settings" shows? If it's adjusting your actual
> maxconns downward it should show there...
>
> On Wed, 29 Oct 2014, Samdy Sun wrote:
>
> > There are no deadlocks, (gdb) info thread
> > * 5 Thread 0xf7771b70 (LWP 24962) 0x080509dd in transmit (fd=431,
> which=2, arg=0xfef8ce48)
> > at memcached.c:4044
> > 4 Thread 0xf6d70b70 (LWP 24963) 0x007ad430 in __kernel_vsyscall ()
> > 3 Thread 0xf636fb70 (LWP 24964) 0x007ad430 in __kernel_vsyscall ()
> > 2 Thread 0xf596eb70 (LWP 24965) 0x007ad430 in __kernel_vsyscall ()
> > 1 Thread 0xf77b38d0 (LWP 24961) 0x007ad430 in __kernel_vsyscall ()
> > (gdb) t 1
> > [Switching to thread 1 (Thread 0xf77b38d0 (LWP 24961))]#0 0x007ad430
> in __kernel_vsyscall ()
> > (gdb) bt
> > #0 0x007ad430 in __kernel_vsyscall ()
> > #1 0x005c5366 in epoll_wait () from /lib/libc.so.6
> > #2 0x0074a750 in epoll_dispatch (base=0x9305008, arg=0x93053c0,
> tv=0xff8e0cdc) at epoll.c:198
> > #3 0x0073d714 in event_base_loop (base=0x9305008, flags=0) at
> event.c:538
> > #4 0x08054467 in main (argc=19, argv=0xff8e2274) at memcached.c:5795
> > (gdb)
> >
> > (gdb) t 2
> > [Switching to thread 2 (Thread 0xf596eb70 (LWP 24965))]#0 0x007ad430
> in __kernel_vsyscall ()
> > (gdb) bt
> > #0 0x007ad430 in __kernel_vsyscall ()
> > #1 0x00a652bc in pthread_cond_wait@@GLIBC_2.3.2 () from
> /lib/libpthread.so.0
> > #2 0x08055662 in slab_rebalance_thread (arg=0x0) at slabs.c:859
> > #3 0x00a61a49 in start_thread () from /lib/libpthread.so.0
> > #4 0x005c4aee in clone () from /lib/libc.so.6
> > (gdb) t 3
> > [Switching to thread 3 (Thread 0xf636fb70 (LWP 24964))]#0 0x007ad430
> in __kernel_vsyscall ()
> > (gdb) bt
> > #0 0x007ad430 in __kernel_vsyscall ()
> > #1 0x005838b6 in nanosleep () from /lib/libc.so.6
> > #2 0x005836e0 in sleep () from /lib/libc.so.6
> > #3 0x08056f6e in slab_maintenance_thread (arg=0x0) at slabs.c:819
> > #4 0x00a61a49 in start_thread () from /lib/libpthread.so.0
> > #5 0x005c4aee in clone () from /lib/libc.so.6
> > (gdb) t 4
> > [Switching to thread 4 (Thread 0xf6d70b70 (LWP 24963))]#0 0x007ad430
> in __kernel_vsyscall ()
> > (gdb) bt
> > #0 0x007ad430 in __kernel_vsyscall ()
> > #1 0x00a652bc in pthread_cond_wait@@GLIBC_2.3.2 () from
> /lib/libpthread.so.0
> > #2 0x080599f5 in assoc_maintenance_thread (arg=0x0) at assoc.c:251
> > #3 0x00a61a49 in start_thread () from /lib/libpthread.so.0
> > #4 0x005c4aee in clone () from /lib/libc.so.6
> > (gdb) t 5
> > [Switching to thread 5 (Thread 0xf7771b70 (LWP 24962))]#0 0x007ad430
> in __kernel_vsyscall ()
> > (gdb) bt
> > #0 0x007ad430 in __kernel_vsyscall ()
> > #1 0x00a68998 in sendmsg () from /lib/libpthread.so.0
> > #2 0x080509dd in transmit (fd=431, which=2, arg=0xfef8ce48) at
> memcached.c:4044
> > #3 drive_machine (fd=431, which=2, arg=0xfef8ce48) at
> memcached.c:4370
> > #4 event_handler (fd=431, which=2, arg=0xfef8ce48) at
> memcached.c:4441
> > #5 0x0073d9e4 in event_process_active (base=0x9310658, flags=0) at
> event.c:395
> > #6 event_base_loop (base=0x9310658, flags=0) at event.c:547
> > #7 0x08059fee in worker_libevent (arg=0x930c698) at thread.c:471
> > #8 0x00a61a49 in start_thread () from /lib/libpthread.so.0
> > #9 0x005c4aee in clone () from /lib/libc.so.6
> > (gdb)
> >
> > strace info, there is the only event named maxconnsevent on epoll?
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 10084037}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 20246365}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 30382098}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 40509766}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 50657403}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 60823841}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 71013006}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 81234264}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 91407508}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 101581187}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 111752457}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 121919049}) = 0
> > epoll_wait(4, {}, 32, 10) = 0
> > clock_gettime(CLOCK_MONOTONIC, {8374269, 132057597}) = 0
> >
> >
> >
> > 在 2014年10月29日星期三UTC+8下午2时47分23秒，Samdy Sun写道：
> > Hello, I got a "memcached-1.4.20 stuck" problem when EMFILE
> happen.
> > Here are my memcached's cmdline "memcached -s /xxx/mc_usock.11201
> -c 1024 -m 4000 -f 1.05 -o slab_automove -o slab_reassign -t 1
> -p
> > 11201".
> >
> > cat /proc/version
> > Linux version 2.6.32-358.el6.x86_64
> (mock...@x86-022.build.eng.bos.redhat.com) (gcc version 4.4.7 20120313 (Red
> Hat 4.4.7-3) (GCC)
> ) #1
> > SMP Tue Jan 29 11:47:41 EST 2013
> >
> > memcached-1.4.20 stuck and don't work any more when it runs for a
> period of time.
> >
> > Here are some information for gdb: (gdb) p stats
> > $2 = {mutex = {__data = {__lock = 0, __count = 0, __owner = 0,
> __kind = 0, __nusers = 0, {__spins = 0,
> > __list = {__next = 0x0}}}, __size = '\000' <repeats 23
> times>, __align = 0}, curr_items = 149156,
> > total_items = 9876811, curr_bytes = 3712501870, curr_conns = 5,
> total_conns = 39738, rejected_conns = 0,
> > malloc_fails = 0, reserved_fds = 5, conn_structs = 1012, get_cmds =
> 0, set_cmds = 0, touch_cmds = 0,
> > get_hits = 0, get_misses = 0, touch_hits = 0, touch_misses = 0,
> evictions = 0, reclaimed = 0,
> > started = 0, accepting_conns = false, listen_disabled_num = 1,
> hash_power_level = 17,
> > hash_bytes = 524288, hash_is_expanding = false, expired_unfetched =
> 0, evicted_unfetched = 0,
> > slab_reassign_running = false, slabs_moved = 20,
> lru_crawler_running = false,
> > disable_write_by_exptime = 0, disable_write_by_length = 0,
> disable_write_by_access = 0,
> > evicted_write_reply_timeout_times = 0}
> >
> > (gdb) p allow_new_conns
> > $4 = false
> >
> > And I found that "allow_new_conns" just set to false when "accept"
> failed and errno is "EMFILE".
> > Here are the codes:
> > static void drive_machine(conn *c) {
> > ……
> > } else if (errno == EMFILE) {
> > if (settings.verbose > 0)
> > fprintf(stderr, "Too many open
> connections\n");
> > accept_new_conns(false);
> > stop = true;
> > } else {
> > ……
> > }
> >
> > If I change the flag "allow_new_conns", it can work again. As below:
> > (gdb) set allow_new_conns=1
> > (gdb) p allow_new_conns
> > $5 = true
> > (gdb) c
> > Continuing.
> >
> > I know that "allow_new_conns" will be set to "true" when
> "conn_close" called. But how could it happen for the case that when
> "accept"
> > failed , and errno is "EMFILE", and this connection is the only one
> for accepting. Notes that curr_conns = 5.
> > Not run out of fd:
> > ls /proc/1748(memcached_pid)/fd | wc -l
> > 17
> >
> >
> > --
> >
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