Date: Thu, 11 Jul 2002 23:00:56 +0200 (CEST) From: Juan Francisco Rodriguez Hervella <jrh@lab.it.uc3m.es> To: Luigi Rizzo <rizzo@icir.org> Cc: Bosko Milekic <bmilekic@unixdaemons.com>, freebsd-net@FreeBSD.ORG Subject: Re: mbuf external buffer reference counters Message-ID: <Pine.LNX.3.96.1020711225805.22207A-100000@lm011.lab.it.uc3m.es> In-Reply-To: <20020711133802.A31827@iguana.icir.org>
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On Thu, 11 Jul 2002, Luigi Rizzo wrote: > Hi, > > certainly removing the malloc will improve performance a lot. > > As I already mentioned to Bosko, in principle the available area > in ext.buffers is irrelevant, and i do not believe this will break > anything (and if it does, it will be easy to fix in the kernel), > but some applications might decide to do writes in multiple of 1K > and trimming away the refcount area might easily result in suboptimal > allocation of storage within the kernel. > First of all, let me say that Im newbie with these topics, I only know a bit about mbufs, but I dont understand how can an application trim away the refcount if the size is MCLBYTES = 2040 - sizeof(refcount). Don't this limit the room which an app. can write ? Thanks. JFRH > I'd probably try to use the same technique as -stable (i.e. have > a separate array for all refcounts), if that is not too bad > from other points of view. > > cheers > luigi > > On Thu, Jul 11, 2002 at 04:20:26PM -0400, Bosko Milekic wrote: > > > > Hi, > > > > Right now, in -CURRENT, there is this hack that I introduced that > > basically just allocates a ref. counter for external buffers attached > > to mbufs with malloc(9). What this means is that if you do something > > like allocate an mbuf and then a cluster, there's a malloc() call that > > is made to allocate a small (usually 4-byte) reference counter for it. > > > > That sucks, and even -STABLE doesn't do this. I changed it this way > > a long time ago for simplicity's sake and since then I've been meaning > > to do something better here. The idea was, for mbuf CLUSTERS, to > > stash the counter at the end of the 2K buffer area, and to make > > MCLBYTES = 2048 - sizeof(refcount), which should be more than enough, > > theoretically, for all cluster users. This is by far the easiest > > solution (I had it implemented about 10 months ago) and it worked > > great. > > > > The purpose of this Email is to find out if anyone has concrete > > information on why this wouldn't work (if they think it wouldn't). > > So, if someone has an example of some broken code somewhere that > > wouldn't like this, please point it out to me now before I go off and > > do this again and commit it. > > > > Thanks, > > -- > > Bosko Milekic > > bmilekic@unixdaemons.com > > bmilekic@FreeBSD.org > > > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > > with "unsubscribe freebsd-net" in the body of the message > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-net" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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