……
Because we also have 32-bit systems and 64-bit applications don't work on
them. So we build memcached on 32-bit system conformably.
在 2014年11月3日星期一UTC+8下午2时56分01秒，Dormando写道：
>
> I don't really know offhand. why are you running 32bit memcached at all?
> Just run it in 64bit mode?
>
> On Sun, 2 Nov 2014, Samdy Sun wrote:
>
> > Thanks, Dormando. I will try with smaller ram memory.
> >
> > 32bit applications can malloc about 3.8G of ram on my 64bit system, so
> "-m 3200" may be ok?
> >
> >
> > 在 2014年11月1日星期六UTC+8上午12时30分29秒，Dormando写道：
> > 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 (
> [email protected]) (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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