Date: Fri, 21 Nov 2014 15:01:13 +0000 From: "Robert N. M. Watson" <rwatson@FreeBSD.org> To: Marko Zec <zec@fer.hr> Cc: Craig Rodrigues <rodrigc@freebsd.org>, FreeBSD Net <freebsd-net@freebsd.org>, "Bjoern A. Zeeb" <bz@FreeBSD.org> Subject: Re: VIMAGE UDP memory leak fix Message-ID: <A4211137-9CE8-45A6-BA73-DCD767236C48@FreeBSD.org> In-Reply-To: <20141121120201.6c77ea5b@x23> References: <CAG=rPVehky00X4MuQQ-_Oe5ezWg52ZZrPASAh9GBy7baYv78CA@mail.gmail.com> <20141121002937.4f82daea@x23> <A4D676B3-6C50-47F7-8CFD-50B44FF4BE98@FreeBSD.org> <9300CB5F-6140-4C49-B026-EB69B0E8B37E@FreeBSD.org> <20141121120201.6c77ea5b@x23>
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On 21 Nov 2014, at 11:02, Marko Zec <zec@fer.hr> 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=
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