Date: Fri, 1 Dec 2000 21:58:21 -0500 (EST) From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> To: dg@root.com Subject: Re: zero copy code review Message-ID: <200012020258.VAA45432@khavrinen.lcs.mit.edu> In-Reply-To: <mit.lcs.mail.freebsd-arch/200012020202.SAA14681@implode.root.com> References: <mit.lcs.mail.freebsd-arch/Pine.BSF.4.21.0012011758110.46782-100000@beppo.feral.com>
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In article <mit.lcs.mail.freebsd-arch/200012020202.SAA14681@implode.root.com> you write: > FreeBSD blocked indefinitly and never returned a NULL pointer. It has never been like that in the FreeBSD era, to my knowledge. 4.3 (or at least 4.3+Wisconsin NFS) slept for mbufs but panicked if it couldn't allocate a cluster; 4.4 as we got it would drain protocols once, for mbufs only, and then return nil if there were still no mbufs free -- thus causing a page-not-present fault a few instructions later as code which assumed M_WAIT could never fail dereferenced the null pointer. Deadlocks may have been possible under 4.3+NFS, if the kernel wanted to allocate a page of physical memory for more mbufs, but all potentially-available memory was both dirty and backed by NFS (think diskless workstation). My guess is that this is why 4.4 did not sleep. -GAWollman -- Garrett A. Wollman | O Siem / We are all family / O Siem / We're all the same wollman@lcs.mit.edu | O Siem / The fires of freedom Opinions not those of| Dance in the burning flame MIT, LCS, CRS, or NSA| - Susan Aglukark and Chad Irschick To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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