Date: Tue, 2 Jun 2020 02:15:53 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Cc: Mark Johnston <markj@FreeBSD.org>, "patrykkotlowski@gmail.com" <patrykkotlowski@gmail.com> Subject: Re: how to fix an interesting issue with mountd? Message-ID: <QB1PR01MB3649C18C37D08A6324AEC81CDD8B0@QB1PR01MB3649.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <QB1PR01MB3649A8589A742A5BD5CB9AE7DD8B0@QB1PR01MB3649.CANPRD01.PROD.OUTLOOK.COM> References: <QB1PR01MB3649A8589A742A5BD5CB9AE7DD8B0@QB1PR01MB3649.CANPRD01.PROD.OUTLOOK.COM>
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Updated slightly from the previous post...=0A=
=0A=
Hi,=0A=
=0A=
I'm posting this one to freebsd-net@ since it seems vaguely similar=0A=
to a network congestion problem and thought that network types=0A=
might have some ideas w.r.t. fixing it?=0A=
=0A=
PR#246597 - Reports a problem (which if I understand it is) where a sighup=
=0A=
is posted to mountd and then another sighup is posted to mountd while=0A=
it is reloading exports and the exports are not reloaded again.=0A=
--> The simple patch in the PR fixes the above problem, but I think will=
=0A=
aggravate another one.=0A=
For some NFS servers, it can take minutes to reload the exports file(s).=0A=
(I believe Peter Erriksonn has a server with 80000+ file systems exported.)=
=0A=
r348590 reduced the time taken, but it is still minutes, if I recall correc=
tly.=0A=
--> If you apply the patch in the PR and sighups are posted to mountd as=0A=
often as it takes to reload the exports file(s), it will simply relo=
ad the=0A=
exports file(s) over and over and over again, instead of processing=
=0A=
Mount RPC requests.=0A=
The current code ignores sighup(s) posted while a reload is in progr=
ess,=0A=
but could still suffer a similar fate if sighups are posted to mount=
d just=0A=
after a reload completes, over and over..=0A=
(I vaguely recall someone reporting that mountd spent hours just rel=
oading=0A=
exports repeatedly.)=0A=
=0A=
So, finally to the interesting part...=0A=
- It seems that the code needs to be changed so that it won't "forget"=0A=
sighup(s) posted to it, but it should not reload the exports file(s) too=
=0A=
frequently.=0A=
--> My thoughts are something like:=0A=
- Note that sighup(s) were posted while reloading the exports file(s) and=
=0A=
do the reload again, after some minimum delay.=0A=
--> The minimum delay might only need to be 1second to allow some=0A=
RPCs to be processed before reload happens again.=0A=
Or=0A=
--> The minimum delay could be some fraction of how long a reload takes=
.=0A=
(The code could time the reload and use that to calculate how lon=
g to=0A=
delay before doing the reload again.)=0A=
=0A=
Any ideas or suggestions? rick=0A=
ps: I've actually known about this for some time, but since I didn't have a=
good=0A=
solution...=0A=
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