Date: Wed, 22 Jan 2003 16:43:12 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: arch@FreeBSD.ORG Subject: Re: M_ flags summary. Message-ID: <15919.4208.394911.712558@grasshopper.cs.duke.edu> In-Reply-To: <20030122155457.A77036@unixdaemons.com> References: <20030122023246.GP42333@elvis.mu.org> <20030121224148.A75236@unixdaemons.com> <20030121.222025.101592442.imp@bsdimp.com> <20030122100253.A76397@unixdaemons.com> <0aef01c2c23d$0f1ae690$52557f42@errno.com> <20030122155457.A77036@unixdaemons.com>
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Speaking as the token 3rd party driver vendor, the removal of
M_WAITOK/M_TRYWAIT is irritating, but not something that can't be
solved with yet another ifdef in my driver. Breaking the 5.0 ABI
prior to 5.1 is no big deal to me, as I don't plan to support
5.0-RELEASE anyway, so I don't care what the #defines end up as in the
5.0-STABLE branch.
My thoughts are that whether we pronounce it po-ta-to, or po-tat-o,
its still a potato and how its pronounced doesn't matter nearly as
much as how it tastes.
The taste "problem" here is that it always used to be safe to sleep
in a process context. That's not true anymore. Now its safe to
sleep in a process context if you're not holding any mutexes. So
there are pleny of sleepable allocation bugs lurking.
If we want to catch sleepable allocation bugs right up front, I
suggest we put this:
if (!(flags & M_NOWAIT)) {
WITNESS_SLEEP(1, NULL);
}
at the top of malloc, and at the top of all entry points to the mbuf
allocator. Eg, before the system has a chance to pull the allocation
off of some cache which will succeed 99.5% of the time, except when
the system is under memory pressure.
Sorry for dragging this in another direction..
Drew
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