Date: Sun, 20 Apr 2008 10:32:25 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: gnn@freebsd.org Cc: net@freebsd.org Subject: Re: zonelimit issues... Message-ID: <20080420102827.U67663@fledge.watson.org> In-Reply-To: <m2hcdztsx2.wl%gnn@neville-neil.com> References: <m2hcdztsx2.wl%gnn@neville-neil.com>
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On Fri, 18 Apr 2008, gnn@freebsd.org wrote: > I am wondering why this patch was never committed? > > http://people.freebsd.org/~delphij/misc/patch-zonelimit-workaround > > It does seem to address an issue I'm seeing where processes get into the > zonelimit state through the use of mbufs (a high speed UDP packet receiver) > but even after network pressure is reduced/removed the process never gets > out of that state again. Applying the patch fixed the issue, but I'd like > to have some discussion as to the general merits of the approach. > > Unfortunately the test that currently causes this is tied very tightly to > code at work that I can't share, but I will hopefully be improving mctest to > try to exhibit this behavior. When you take all load off the system, do mbufs and clusters get properly freed back to UMA (as visible in netstat -m)? If not, continuing to bump up against the zonelimit would suggest an mbuf/cluster leak, in which case we need to track that bug. You might consider adding a debugging-only zonelimit waiter count to the UMA zone, and checks/assertions that a wakeup is being generated properly. That is, to confirm that the wakeup is generated when memory is freed up if there are threads waiting. There is at least one as-yet MFC'd fix to the sleep/wakeup code, I believe, that might be relevant here. Is the problem you're reporting on 7.x, or on 8.x? If 8.x, that's probably not it, but if 7.x, it could be. (This same sleep/wakeup bug occasionally leads to wedging of dump(8), I believe). Robert N M Watson Computer Laboratory University of Cambridge
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