From owner-freebsd-arch@FreeBSD.ORG  Sat Mar 22 13:57:39 2008
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: arch@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id D7CA5106566B;
	Sat, 22 Mar 2008 13:57:39 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from cyrus.watson.org (cyrus.watson.org [209.31.154.42])
	by mx1.freebsd.org (Postfix) with ESMTP id B94018FC1A;
	Sat, 22 Mar 2008 13:57:39 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from fledge.watson.org (fledge.watson.org [209.31.154.41])
	by cyrus.watson.org (Postfix) with ESMTP id F162146B4C;
	Sat, 22 Mar 2008 09:57:38 -0400 (EDT)
Date: Sat, 22 Mar 2008 13:57:38 +0000 (GMT)
From: Robert Watson <rwatson@FreeBSD.org>
X-X-Sender: robert@fledge.watson.org
To: Ruslan Ermilov <ru@FreeBSD.org>
In-Reply-To: <20080322105145.GA41672@team.vega.ru>
Message-ID: <20080322135637.Y6961@fledge.watson.org>
References: <20080322105145.GA41672@team.vega.ru>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: arch@FreeBSD.org
Subject: Re: Disposal of a misleading M_TRYWAIT
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 22 Mar 2008 13:57:39 -0000

On Sat, 22 Mar 2008, Ruslan Ermilov wrote:

> I'd like to remove the misleading uses of M_TRYWAIT throughout the tree and 
> clean up some dead code that assumes its original behavior (that it could 
> return NULL).
>
> Since the advent of MBUMA in FreeBSD (whatever), M_TRYWAIT has meant 
> M_WAITOK.  (The reason for M_TRYWAIT itself was that an original mbuf's 
> M_WAIT could return NULL.)
>
> There is little or no sign that this will change, and there are lots of 
> consumers that already pass M_WAITOK to mbuf allocator routines and rely on 
> its invariants, so support for the concept of M_TRYWAIT has rotted and would 
> have to be re-written anyway if reintroduced.
>
> http://people.freebsd.org/~ru/patches/M_TRYWAIT.patch

This seems reasonable to me for exactly the reasons you stte.  We might 
simultaneously want to complete the M_DONTWAIT -> M_NOWAIT conversion.  And 
you can then remove the XXX comment in mbuf.h about phasing out M_TRYWAIT and 
M_DONTWAIT.  :-)

Robert N M Watson
Computer Laboratory
University of Cambridge