From owner-freebsd-net@FreeBSD.ORG Fri Nov 21 15:01:20 2014 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id BCCEA4CA; Fri, 21 Nov 2014 15:01:20 +0000 (UTC) Received: from cyrus.watson.org (cyrus.watson.org [198.74.231.69]) by mx1.freebsd.org (Postfix) with ESMTP id 95AEDC05; Fri, 21 Nov 2014 15:01:20 +0000 (UTC) Received: from c0198.aw.cl.cam.ac.uk (c0198.aw.cl.cam.ac.uk [128.232.100.198]) by cyrus.watson.org (Postfix) with ESMTPSA id F3EE946B3F; Fri, 21 Nov 2014 10:01:15 -0500 (EST) Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: VIMAGE UDP memory leak fix From: "Robert N. M. Watson" In-Reply-To: <20141121120201.6c77ea5b@x23> Date: Fri, 21 Nov 2014 15:01:13 +0000 Content-Transfer-Encoding: quoted-printable Message-Id: References: <20141121002937.4f82daea@x23> <9300CB5F-6140-4C49-B026-EB69B0E8B37E@FreeBSD.org> <20141121120201.6c77ea5b@x23> To: Marko Zec X-Mailer: Apple Mail (2.1878.6) Cc: Craig Rodrigues , FreeBSD Net , "Bjoern A. Zeeb" X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Nov 2014 15:01:20 -0000 On 21 Nov 2014, at 11:02, Marko Zec wrote: >> I had convinced myself for UDP many years ago that it was ok to >> remove it. People have touched the code however so it=92s = definitively >> worth re-checking again. >>=20 >> For TCP we clearly cannot do it (yet, and couldn=92t back then). = But >> TCP was the only of the few cases I had left unfixed back then. >> Can=92t remember what the others were (was like 3 or 4 of them; = could >> also be some of the fixes were indeed committed back then. >=20 > Now that we've found ourselves in this discussion, I'm really > becoming curious why exactly do we need UMA_ZONE_NOFREE for network > stack zones at all? Admittedly, I always thought that the primary > purpose of UMA_ZONE_NOFREE was to prevent uma_reclaim() from paging = out > _used_ zone pages, but reviewing the uma code reveals that this might > not be the case, i.e. that NOFREE only prevents _unused_ pages to be > freed by uma_reclaim(). >=20 > Moreover, all uma_zalloc() calls as far as I can see are flagged as > M_NOWAIT and are followed by checks for allocation failures, so that > part seems to be covered. >=20 > So, what's really the problem which UMA_ZONE_NOFREE flagging is = supposed > to solve these days? (you claim that we clearly need it for TCP - = why)? Bjoern and I chatted for the last twenty or so minutes about the code, = and believe that as things stand, it is *not* safe to turn off = UMA_ZONE_NOFREE for TCP due to a teardown race in TCP that has been = known about and discussed for several years, but is some work to resolve = and that we've not yet found time to do so. The XXXRW's in tcp_timer.c = are related to this. We're pondering ways to fix it but think this is = not something that can be rushed. Robert=