Date: Thu, 7 Dec 2017 20:12:36 -0800 From: Mark Millard <markmi@dsl-only.net> To: Larry McVoy <lm@mcvoy.com> Cc: freebsd-hackers@freebsd.org Subject: Re: OOM problem? Message-ID: <80D1ECE3-D983-4DFB-9B28-3F716F73CD47@dsl-only.net> In-Reply-To: <20171208011430.GA16016@mcvoy.com> References: <20171208011430.GA16016@mcvoy.com>
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[Just a pointer to a potential example report on the lists.] On 2017-Dec-7, at 5:14 PM, Larry McVoy <lm at mcvoy.com> wrote: > . . . > It's sort of an ugly problem in that > when it happens your only recourse is to power cycle the machine, you > can't kill off the processes causing the problem. If there is a serial console, can something like, say, CR TILDE CTRL-B get to the db> prompt? (options ALT_BREAK_TO_DEBUGGER example.) > . . . > > Here is the problem. All of these "misbehaved" (by using lots of ram) > processes go to sleep, I believe in vm_wait(). They are all waiting > for more ram so the pageout daemon is kicked but to no avail, all the > ram is tied up in the processes that want more ram. The pageout daemon > kicks out what it can but it quickly gets to the point that it scans > everything and finds nothing (I know this because I added debugging to > show that's what it is doing). > > The OOM code kicks in and it behaves poorly. It doesn't kill any of > the big processes, those are all sleeping without PCATCH on so they are > skipped. The OOM code starts killing off anything it can find, it was > killing getty, ssh, bash, dhclient. One buglet is that, in my opinion, > it finds stuff to kill that it probably shouldn't. Anything that init > will respawn is fine, anything that would not be respawned should be > run as not killable. Seems like an audit of those processes might be > in order. https://lists.freebsd.org/pipermail/freebsd-hackers/2017-December/051890.html may be an example of the problem on a rpi2 but with a swap partition in use. I was able to get to the db> prompt and included some basic information from there. It was head -r326192 based. (I did eventually reboot the rpi2 so I no longer have that specific context available to examine.) > I know that you'll ask why no swap? Just add swap and the problem > goes away. Does it? I don't think so, that's just kicking the can > down the road. If we add 256GB of swap now we have a 512GB bag to fill, > fill that and I think we're right back to where we started. > > . . . === Mark Millard markmi at dsl-only.net
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