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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] tools/xenstore: claim resources when running as daemon
On 17.05.21 17:55, Julien Grall wrote: Hi Juergen, On 17/05/2021 07:47, Juergen Gross wrote:On 14.05.21 22:19, Julien Grall wrote:Hi Juergen, On 14/05/2021 09:41, Juergen Gross wrote:Xenstored is absolutely mandatory for a Xen host and it can't be restarted, so being killed by OOM-killer in case of memory shortage is to be avoided. Set /proc/$pid/oom_score_adj (if available) to -500 in order to allow xenstored to use large amounts of memory without being killed. In order to support large numbers of domains the limit for open file descriptors might need to be raised. Each domain needs 2 file descriptors (one for the event channel and one for the xl per-domain daemon to connect to xenstored).Hmmm... AFAICT there is only one file descriptor to handle all the event channels. Could you point out the code showing one event FD per domain?I have let me fooled by just counting the file descriptors used with one or two domain active. So you are right that all event channels only use one fd, but each xl daemon will use two (which should be fixed, IMO). And thinking more about it it is even worse: each qemu process will at least require one additional fd.Try to raise ulimit for open files to 65536. First the hard limit if needed, and then the soft limit.I am not sure this is right to impose this limit to everyone. For instance, one admin may know that there will be no more than 100 domains on its system.Is setting a higher limit really a problem?I am quite unease to set a limit that nearly nobody will reach unless something went horribly wrong on the system. Hmm, I really don't see the downside of having the possibility to let xenstored open lots of files. Anyway we can do it via prlimit if you like that better. So the admin should be able to configure them. At this point, I think the two limit should be set my the initscript rather than xenstored itself.But the admin would need to know the Xen internals for selecting the correct limits. In the end I'd be fine with moving this modification to the script starting Xenstore (which would be launch-xenstore), but the configuration item should be "max number of domains to support".I would be fine with "max numer of domains to support". What I care the most here is the limits are actually applied most of (if not all) the time. I did another test and found: - the xl daemon for a guest will use 2 socket connections - qemu for a HVM guest will use 3 socket connections - qemu for a PV guest is using one socket connection - 14 other files are used by xenstored So we should set the limit to 5 * n_dom + 100 (some headroom will be nice IMO). This would also avoid the problem where Xenstored is not allowed to modify its limit (see more below).Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- tools/xenstore/xenstored_core.c | 2 ++ tools/xenstore/xenstored_core.h | 3 ++ tools/xenstore/xenstored_minios.c | 4 +++tools/xenstore/xenstored_posix.c | 46 +++++++++++++++++++++++++++++++4 files changed, 55 insertions(+)diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.cindex b66d119a98..964e693450 100644 --- a/tools/xenstore/xenstored_core.c +++ b/tools/xenstore/xenstored_core.c @@ -2243,6 +2243,8 @@ int main(int argc, char *argv[]) xprintf = trace; #endif + claim_resources(); + signal(SIGHUP, trigger_reopen_log); if (tracefile)tracefile = talloc_strdup(NULL, tracefile); diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.hindex 1467270476..ac26973648 100644 --- a/tools/xenstore/xenstored_core.h +++ b/tools/xenstore/xenstored_core.h @@ -255,6 +255,9 @@ void daemonize(void); /* Close stdin/stdout/stderr to complete daemonize */ void finish_daemonize(void); +/* Set OOM-killer score and raise ulimit. */ +void claim_resources(void); + /* Open a pipe for signal handling */ void init_pipe(int reopen_log_pipe[2]);diff --git a/tools/xenstore/xenstored_minios.c b/tools/xenstore/xenstored_minios.c It would be possible to set the OOM-score from the launch script, too. + + fd = open(path, O_WRONLY); + /* Do nothing if file doesn't exist. */Your commit message leads to think that we *must* configure the OOM. If not, then we should not continue. But here, this suggest this is optional. In fact...I can modify the commit message by adding a "Try to".+ if (fd < 0) + return; + /* Ignore errors. */ + write(fd, val, sizeof(val));... xenstored may not be allowed to modify its own parameters. So this would continue silently without the admin necessarily knowning the limit wasn't applied.I can add a line in the Xenstore log in this regard.This feels wrong to me. If a limit cannot be applied then it should fail early rather than possibly at the wrong moment a few days (months?) after. I think issuing a warning would be better here. We are running with no OOM adjustments since years now. Juergen Attachment:
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